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Airbus has declared its intent to have a clean sheet hydrogen powered airliner in commercial service by 2035. Ms. Simpson will address the challenges associated with incorporating cryogenics into an aircraft and share the progress of some of projects Airbus is pursuing to solve them.
https://www.cec-icmc.org/2023/awards/
The current research develops a finite volume-based Computation Fluid Dynamic (CFD) model utilizing an Energy of Fluid (EOF) approach to generate a simulation of the densification of liquid hydrogen (LH2) in the Integrated Refrigeration and Storage (IRAS) experimental tank for the Ground Operations Demonstration Unit for Liquid Hydrogen Project (GODU-LH2) at the Kennedy Space Center (KSC). The computational code will integrate a commercial software pressure-based model with User Defined Functions (UDF) generated and added to the model. The modified model will solve the energy equation in terms of internal energy and provide temperature and pressure calculations for a given tank geometry. This method will decrease computational time when compared to the built-in commercially available Enthalpy solvers. Currently the research focused on utilizing User Defined Scalars (UDS) compared to the enthalpy model and a lumped node analysis to show the written UDS is as accurate as the built-in solvers, and the models will be verified using known solutions for solidification and validated with the experimental results from the Cryogenics Test Laboratory (CTL) at KSC for the IRAS densification process.
Boiling heat transfer of cryogenic fluid is strongly related with various industrial field such as liquefied natural gas (LNG), superconducting electromagnet, and hydrogen plant, which have recently been in the spotlight as eco-friendly energy. To reach the operation temperature, initial cooldown process of the cryogenic system is an important issue in terms of coolant consumption and the corresponding cost. When the cryogenic fluid directly starts to contact the surface of a metal object at room temperature in the initial cooling, a film boiling heat transfer occurs due to a large temperature difference and the heat transfer rate is limited by vapor film between the cryogenic fluid and solid surface. It is known that a thin surface coating of solid surface with low thermal conductivity material can increase the cooling speed by increasing the Leidenfrost temperature and the peak nucleate boiling. In this paper, Stainless Steel 316L, Copper, and Aluminum 6061 test specimens coated with Teflon, Epoxy, and Polyimide tape are prepared and cooldown experiments are conducted in a bath of liquid nitrogen to investigate the enhanced boiling heat transfer. By applying a thin surface coating of less than 200 µm, it is possible to reduce the initial cooldown time by about 50%. The boiling curve is obtained using the Inverse Heat Conduction Method (IHCM). As a result, it is verified that an appropriate surface coating increases the effective Leidenfrost temperature through the thin, low thermal conductive coating layer, as well as the peak nucleate heat transfer rate due to the modified surface condition. The results of this study are expected to be used to improve the initial cooldown rate of metals used in cryogenic systems.
A 1.8K superfluid 4He system could be used in many cryogenic devices, such as the separation of helium isotopes and the advanced superconducting accelerator. Cryogenic stop valve is one of the most important part of the 1.8K system. Simulation studies on heat transfer were made by ANSYS. According to the simulated data, the heat loss was reduced by 60% when the double heat sinks were welded and the stem tube was made of materials with low thermal conductivity. The seal-technology was brought for the stop valve in the low temperature. The leakage rate of the stop valve was analyzed and tested in the normal temperature and in the low temperature. The result of the tests showed the stop valve has stable valve seat sealing performance.
In the development process of cryogenic valves, liquid nitrogen is usually used as the cooling medium to carry out relevant performance tests. When the temperature is lower than 77 K, for example, for liquid hydrogen valves, expensive liquid helium is usually used as the cooling medium due to safety concerns. In this paper, a cryogenic test equipment is designed to test the take-off characteristics and sealing performance of liquid hydrogen safety valves (covering volume is about φ350-700 mm), which is cooled by a G-M cryocooler. The construction of the test equipment, the test procedure, and the relevant thermal design to ensure that the large valve can achieve rapid cooling and good temperature uniformity will be covered. Besides, the experimental results based on a 2-inch liquid hydrogen safety valve will also be presented.
Abstract. Cryogenic valve sealing technology is notoriously more challenging than traditional fluids due to the combination of small atoms and molecules with extreme temperature and pressure profiles. Recently, flexible polymeric films folded into origami demonstrated considerable resilience to mechanical failure in the cryogenic extreme. Showing that thin, fluorinated polymers such as Polytetrafluoroethylene (PTFE) are observed to not plastically deform in cryogenic conditions when compared to thick geometries. This paper explores a new cryogenic valve sealing paradigm which uses multiple conformable polymer layers to provide constant seat mating surface area at cryogenic conditions. Stacking these thin discs in series with a spacer allows maximum bend around the seat while creating multiple sealing surfaces. A theoretical model of thin shell deformation is developed to determine likely failure mechanisms and utilized for valve design. Experimental measurements of leakage rates with and without the presence of Foreign Object Debris (FOD) are compared with traditional re-closable pressure relief valves. Conformable cryogenic valve seats have the potential to be more repeatable, decrease leakage rates due to coefficient of thermal expansion, hysteresis, and FOD when compared to traditional market valves.
Industrial valves for cryogenic application are typically made of austenitic stainless steel. A new design has been developed, where stem and extended bonnet are made of glass fiber reinforced PEEK (PEEK/GF). This material has a significant lower heat conductivity and lower specific weight. Therefore valves with minimized heat input as well as very compact and lightweight valves can be realised.
The results of measurements of the permeation behaviour of virginal composite as well as composite with permeation barrier are shown. Further measurement results of the rate of heat flow of composite samples and the whole valve assembly have been performed. The novel valve design will be introduced.
The laminate structure has been designed by herone GmbH to withstand the mechanical load due to system pressure and valve actuation. The wall thickness is slightly higher than valve made of stainless steel. Test specimen have been made to perform measurements on thermal conductivity und permeation.
The permeation rate of PEEK/GF is very high compared to stainless steel, this can cause problems in later applications. Therefore test specimen with interlaminar metal foil have been investigated. Metal foils made of stainless steel with a thickness of 10 µm already decreased the permeation rate of about two orders of magnitude compared to natural PEEK/GF (see Figure 1, right side). Foils with a thickness up to 100 µm have been investigated.
Large-scale helium cryogenic refrigeration facilities are indispensable equipment for many cutting-edge researches, and the cold compressor is the most advantageous pressurization scheme in superfluid helium systems with capacity of more than 200 watts. Due to the extremely low operating temperature zone of the cold compressor, the efficiency of the compression process decreases as the external heat leakage increases, especially when building systems with greater cooling capacity, this phenomenon becomes more significant. In order to reduce the influence of heat leakage, a conjugate heat transfer analysis is carried out on the cold compressor using commercial CFD software, and the internal structures, including thermal anchor, thermal insulation materials, are analyzed and optimized base on the simulations.
With the large-scale development of hydrogen energy, liquid hydrogen is the only way to break through the bottleneck of the large-scale and commercial operation of the entire hydrogen energy system, and also the only way to achieve the goal of "carbon neutrality". The orifice-type hydrostatic gas bearing lubricated by hydrogen plays an important role in cryogenic turbo expander in large hydrogen liquefier. In the hydrogen turbine expander, a heavy rotor is used to support the expansion impeller for hydrogen liquefaction with large flow. The influence of low density lubricating gas on heavy rotors at high speed and the effect of these parameters such as gas film gap, rotating speed, supply gas pressure on the static and dynamic characteristics were studied in this paper.
The orifice throttling hydrostatic gas bearing has the advantages of simple structure, long service life and easy to reach the expected speed, it has been widely used in the field of high-precision machinery. The orifice throttling hydrostatic thrust gas bearing plays an important role in the development of helium cryogenic turbo expander. A numerical analysis on the orifice-type hydrostatic gas bearing is carried out to study the relationship between the static and dynamic characteristics and the parameters, such as the rotating speed、gas film gap and so on. The reason of the air hummer is also analyzed, the air phenomenon is closely to the volume、depth and the pressure of the air chamber.
An experimental helium liquefier/refrigerator, using ultra high speed cryogenic turbo-expanders is designed and developed in Technical Institute of Physics and Chemistry (TIPC), and liquefaction rate of around 42 L/hr and refrigeration capacity of around 130W@4.5K is achieved. The turbo-expander constitutes the most critical component of a helium liquefier/refrigerator causing that the turbine efficiency has a great influence on the performance of the whole cryogenic process plant. Inlet Flow Radial (IFR) turbine design is dictated by criteria like velocity ratios. For small flow rate plants the size of the turbine impeller needs to be reduced. In order to reach a high efficiency, the rotational speed must be increased to complete a large specific enthalpy drop. The present article describes the latest technical developments at TIPC, including results obtained during field trials with the TIPC helium liquefier and refrigerator. The motivation of these developments is to improve the efficiency of the machines, and also to widen the range of operation.
The characteristics of gas lubrication of tilting pad gas bearing make it have higher load capacity and lower friction force, and it is widely used in the field of high-speed turbine machinery. Especially in the special environment of low temperature, dynamic pressure gas bearings do not need additional bearing gas system to assist, greatly simplifying the system structure. However, the performance of dynamic pressure gas bearing is limited by the structure, especially depends on the machining accuracy and manufacturing technology. Based on the theoretical calculation and experimental analysis of tilting tile gas bearing, a bearing structure with good operation, high speed and good bearing capacity under low temperature environment is proposed in this paper. The simulation results show that the stability of the tilting pad gas bearing is improved by the improvement of the pressure distribution of the fulcrum, and the effects of heat transfer temperature, friction force and other factors on the static and dynamic performance of the bearing are discussed.
After nearly 20 years of long-term operation, the variable frequency driver (VFD) of the Main Cryogenic Plant 1 (MCP1) suffered a major failure after a routine shutdown in September 2021. After inspection and replacement of damaged parts, the cause of the failure cannot be found. And some normal spare parts were damaged. Since most of the spare parts are out of production and we still have two same type of VFD in operation. In order to keep spare parts for the other two VFD. We decided to upgrade the whole VFD for the MCP1. After some customized changes, this new VFD has been refitted and started testing in the end of 2021. During the process of dismount the original VFD, we found the reason of the fault, which was a short-circuit occur by power wire damaged. In this paper, I will describe the differences between the original and new VFD, the customized changes, and the test results of the completely system. The failure reason and damage by the old VFD will also present.
The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration in Lund, Sweden. An essential part of the project is the linear 2.0 GeV proton accelerator. Its superconducting part is designed to comprise 13 spoke and 30 elliptical cryomodules that are cooled at 2K. The cryogenic distribution system (CDS) connects the refrigeration plant with the cryomodules via multi-transfer lines, individual valveboxes for every cryomodule and an endbox. It is designed, manufactured and installed under the responsibility of two ESS in-kind partners. The CDS for the spoke cryomodules (CDS-sp) is supplied by IJCLab, France, the CDS for the elliptical cryomodules (CDS-el) is supplied by WUST, Poland. Pre-commissioning, commissioning and operation is done by ESS whereby IFJ PAN contributed with valuable advice.
Pre-commissioning activities like loop checks, temperature curve validation, pressure sensor calibration or valve initialization and leak tightness tests followed after mechanical or electrical completion of the respective CDS parts and started in summer 2022. Eventually, the system was ready for commissioning and a first cooldown was performed in December 2022. Goal of this commissioning was to acceptance test and check of the system before the cryomodule installation in the tunnel starts in March 2023.
The paper describes diverse challenges regarding valves, sensors and system control. Preliminary test results and lessons learnt are discussed as well as an outlook of the upcoming plans are given.
Keywords: helium liquefaction, refrigeration, 2K, cryogenic valves, heat load measurements, temperature measurements, controls, sensors, calibration
The ITER Neutral Beam Test Facility (NBTF), is hosted in Padova, Italy and includes the MITICA experiment – a full-scale prototype of the ITER heating neutral beam injector (HNB). The large cryopump is intended to absorb the gas used to neutralize the high energy beams of the MITICA experiment. The cryopump is cooled by a dedicated cryogenic plant which was procured by Fusion for Energy (F4E) in 2016.
AL-AT (Air Liquide Advanced Technologies) has taken part to the project by supplying the cryogenic plant. The plant includes the refrigerator associated to its compressor station, oil removal system, auxiliary cold box, dedicated for supply of SHe flow for the cryopanels and GHe flow for thermal shields and equipped with magnetic bearing cold circulators, cryogenic transfer lines, storage tank for helium gas, analysers, atmospheric heater, water cooling system and LN2 phase separator.
The aim of this paper is to present the main technical features of the overall cryogenic system and the main results of the commissioning phase of the refrigerator. The commissioning and testing results are reported detailing the simulated stand-by operational mode. AL-AT faced some issues with thermo-acoustic oscillations during the commissioning. This paper will introduce the state-of-the-art on this issue, and detail the implemented solutions to identify the source of the vibration and to solve the problems so that the required performance was fully demonstrated.
The increase over the last years of the testing activities related to superconducting quantum materials, SRF cavities for the PIP-II and the LCLS-II projects, as well as superconducting magnets for the HL-LHC project and Fusion research activities, has required the addition of a new Helium cryogenic plant into the existing IB-1 Industrial Cryogenic Test Facility.The new cryogenic plant is composed of a cryogenic liquefier (Cold Box) able to provide up to 340 L/h, a 4kL Dewar and two Mycom compressors providing up to 120 g/s. AL-AT (Air Liquide Advanced Technologies) has taken part of this project by designing and manufacturing the cryogenic liquefier. This new cryogenic plant is connected through a cryogenic distribution system to a 10 kL Dewar, which is part of the existing cryogenic test facility, itself composed of another Cold Box and a Sullair compressor. The new cryogenic plant has two main operating modes: one allows to transfer liquid helium at 1.7 bar between the two Dewars, the other allows to transfer supercritical Helium at 2 bar or more between the new Cold Box and the 10 kL Dewar. The entire industrial cryogenic facility is handled by a common Inventory Control System, composed of three regulatory valves, and 9 tanks giving a total buffer volume of more than 1000 m3. This paper presents the technical features of the new Helium cryogenic plant, as well as the main results of the liquefier commissioning phase and details of the helium transfer between the two dewars, making the connection between the cryogenic plants at the IB-1 Industrial Cryogenic Test Facility.
The Second Target Station (STS) at Oak Ridge National Laboratory will be a 700 kW pulsed spallation neutron source designed to provide the world’s highest brightness cold neutron beams. In order to produce the required neutron performance, two compact liquid hydrogen moderators are located adjacent to the tungsten spallation target and must be supplied with less than 20K hydrogen and a para hydrogen fraction of 99.8% or greater. The Cryogenic Moderator System (CMS) will consist of a single hydrogen loop feeding the two moderators in series cooled by a helium refrigerator with a cooling capacity of 2.5 kW at 17K. The hydrogen loop consists of a hydrogen circulator, hydrogen helium heat exchanger, ortho-para converter, accumulator, transfer lines and heater. The design of the hydrogen loop is based on the CMS design of the First Target Station at the Spallation Neutron Source and some of the component designs may be reused. General hydrogen temperature control is provided by controlling the flowrate of helium to the heat exchanger. The hydrogen loop will have a constant flowrate of 0.5 L/s and remove a nuclear heat load of about 850 W from the two moderators, which is deposited both directly in the hydrogen and the adjacent hydrogen containing structures. Because the nuclear heat load is accelerator driven, the hydrogen system must remain stable when the heat load is removed instantaneously during beam trips. System stability is maintained passively with the accumulator and actively with the heater. Ionizing radiation which interacts with the liquid hydrogen drives backconversion of the hydrogen from parahydrogen to orthohydrogen. The STS moderator performance is very sensitive to small fractions of orthohydrogen requiring an ortho-para converter to maintain the hydrogen supplied to the moderators at near equilibrium parahydrogen concentration. STS CMS is in the early stage of preliminary design and current focus is evaluating component sizing and system stability during beam transients.
The Spallation Neutron Source (SNS) incorporates a 20-K helium refrigeration system to cool three circuits supplying cold hydrogen to neutron moderators. The helium refrigeration system consists of a warm compressor, oil removal, purifier, 20-K cold box, and three helium-hydrogen heat exchangers. The hydrogen loops consist of a circulator, moderator, accumulator with expandable bellows, and the heat exchangers. Historically, the cryogenic system has had periods of instability and has operated with a reduced capacity. While performing the Proton Power Upgrade, the proton beam power on the first target station will increase from 1.4 MW to 2 MW. This will result in a 43% increase in dynamic load to the cryogenic system. The first directive in preparing the system for higher beam power was to achieve consistent operational stability at 1.4 MW beam power. After this was achieved, the next task was to increase the system capacity. This paper will describe the initiatives taken to produce consistent high-capacity performance.
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) operates the Cryogenic Moderator System (CMS) which provides supercritical hydrogen cooling at 20K to three neutron moderators. A helium refrigerator provides 8 kW of cooling capacity to three parallel hydrogen circuits. Several projects have been completed to improve operational reliability CMS. The status of helium compressor oil removal system, helium oil processor, helium purity monitoring, hydrogen circulator bearing investigation and operational procedure improvement will be presented. Future plans for sustained reliable operation at design capacity will also be presented.
At the ESS target, high energy spallation neutrons are produced by impinging a 5 MW proton beam on the high-Z material, tungsten. The proton beam is pulsed with a repetition of 14 Hz and a pulse length of 2.86 ms. The moderator system consists of a water pre-moderator and two liquid hydrogen cold moderators, which are optimized to achieve a high cold neutron brightness. The neutronic performance of the cold moderators degrades rapidly with the decreasing parahydrogen fraction below 99.5%. The neutron collisions in the cold moderators increase the orthohydrogen fraction unless compensated by the ortho- to parahydrogen conversion driven by the catalyst system. Therefore, the Cryogenic Moderator System (CMS) is equipped with an ortho-parahydrogen (OP) catalyst to maintain the desirably high parahydrogen fraction. The ortho-to-parahydrogen ratio will be measured by the in-situ measurement system (OPMS) by means of a Raman spectroscopy currently being developed. A dedicated sampling line with a sapphire window for the OPMS has been designed in order to continuously measure fractions of ortho- and parahydrogen from and to the moderators. The sampling line has been installed at the ESS site in 2022. It could be demonstrated that our developed sapphire window, through which the laser and backscattered photons travel, can endure the required pressure and thermal cycles in liquid hydrogen environment. We have confirmed that there was no harmful leak by the helium leak testing after both 3,000 pressure-cycles between 0.1 and 1.7 MPa in liquid hydrogen and 100 thermal-cycles between 250 K and 20 K. The Raman optics system with a precision of 0.1% parahydrogen fraction is developed to detect an undesirable shift towards a higher orthohydrogen fraction caused by para-to-ortho back conversion driven by the neutron collisions in the cold moderators.
The European Spallation Source (ESS) is a multi-disciplinary research facility based on the world’s most powerful neutron source. One key component of the target station is the cryogenic moderator system (CMS) which is designed and manufactured by the ZEA-1 of the Forschungszentrum Jülich. The cryostat of the CMS supplies liquid hydrogen in a closed loop at the temperature of around 18.5K and a pressure of 10 bar.abs to the moderator vessels, where neutrons interact with the hydrogen and get slowed down. The neutron moderation process can produce an average of 17.3 kW of heat, and considering the additional 5.9 kW of heat input from the pumps, the total heat that must be removed by a continuous stream of liquid hydrogen adds up to 23.1 kW. The flow is generated by two redundant hydrogens pumps which can circulate one kilogram of liquid hydrogen per second. At ESS the required cooling capacity is provided by helium refrigeration plant with ca. 30.2 kW cooling power at 15 K (Target Moderator Cryoplant TMCP) which interfaces to the Cryogenic Moderator System via two heat exchangers inside the cryostat. A major challenge during the factory acceptance test (FAT) in Jülich was the lack of a refrigeration system. In order to still be able to carry out the CMS cryostat cold test with liquid nitrogen instead of liquid hydrogen, gaseous nitrogen with a controlled temperature between 300K and 100 K is fed to the He side of the cryostat. A mixing plant was specially designed and built for this purpose, which mixes liquid nitrogen and gaseous nitrogen at room temperature in such a way that a gas flow with a PID-controlled temperature is produced. Above all, keeping the temperature stable at different pump speeds was a major but necessary challenge, because the temperature gradient across the heat exchanger between the secondary and primary side must not exceed a maximum of 40K. Finally, after the successfully completed FAT, the cryogenic moderator system was delivered to Sweden and integrated into the target station of the ESS.
The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) houses an aging reactor that serves about 40% of all cold neutron research needs in the U.S. First critical in 1967, the National Bureau of Standards Reactor (NBSR) is now more than 50 years old. NCNR engineers have initiated a design effort for a replacement reactor – namely the NIST Neutron Source or NNS. The NNS is conceived as a 20-MWth light-water cooled and moderated, and heavy-water reflected compact core design. The NNS will include two liquid deuterium cold sources to moderate neutrons. These cold sources will require new cryogenic infrastructure to operate. This report describes a preliminary proposed design concept for the NNS cold sources and associated ancillary infrastructure.
Abstract- The 325MHz Single Spoke Resonator 1 (SSR1) twelve cavities Cryomodule (CM) is 5.3-meter length and it has 288 liter liquid helium @ 2K mode, The High Beta 650 MHz (HB650) six elliptical cavity cryomodules is 9.92 meter and it has 530 liter liquid helium @2K mode. The SSR1 and HB650 CM had been tested at Fermilab PIP2 IT in the Cryomodule Test Facility (CMTF). Their synoptic/EPICS cryogenic control system includes the Siemens Process Control System S7-400, Automation Direct DL205 PLC and remote synoptic/EPICS Phoebus GUI. This paper presents a method which has been successfully used by Fermilab PIP2 IT cryogenic remote on-line, real-time control systems.
Index: PIP-II SSR1 and HB650 CM, cryogenic control system, synoptic/EPICS IOC OPC UA
The cryogenic distribution system (CDS) at the European Spallation Source (ESS) connects the refrigeration plant with the linear accelerator, consisting in 13 spoke and 30 elliptical cryomodules that are cooled at 2K via multi-transfer lines, individual valveboxes for every cryomodule and an endbox. The designed control system monitors and controls the cooling helium flow through the CDS.
The controls architecture for the CDS is based on one Programmable Logic Controller (PLC) per valvebox and another one for the endbox, which are integrated into EPICS through the Controls Network and takes care of the process functions, making it a total of 44 PLCs. This type of integration allows for the remote operation of the CDS from the control room and the necessary interaction of the control system with other related systems and EPICS services like archiving, alarms and save-and-restore.
Pre-commissioning activities like loop checks, temperature curve validation, pressure sensor calibration and valve initialization started in summer 2022. Eventually, the system was ready for commissioning and a first cooldown was performed in December 2022.
The paper describes the design, development and commissioning of the control system and diverse challenges during the deployment and commissioning activities. Future activities are discussed including the implementation of a sequencer for automatic cooldown and warmup, integration with the cryomodule controls and a master PLC to handle the helium management.
Chambers A and B are two large thermal vacuum chambers at Johnson Space Center which enable space simulation for unmanned and human-rated missions, respectively. With the resurgence in deep space missions for scientific research and various private commercial ventures, these chambers are expected to be used frequently for at least the next decade. For qualifying the James Webb Space Telescope, upgrades to Chamber A were performed which included the addition of a 12.5 kW refrigeration system with helium shrouds capable of simulating deep space environment and an efficient and reliable LN2 natural flow thermosiphon system for the thermal shield. Continuous improvements since then have focused on ensuring operational readiness by modernizing the data acquisition, recording, controls, and visualization systems for both chambers and clean room. These upgrades will be the focus of this paper.
Controlling the Cryochambers was enhanced by moving from a 32-bit SCADA system to a 64-bit architected system. Infrastructural changes involved installing redundant power circuits, adding new servers, network switches, and including load balancing with fail-over between servers to minimize downtime. Instead of distributed servers, 3 redundant servers are used to share configurations. Configurations are now kept in a shared SQL instance making it easy to deploy and maintain.
During this upgrade process many sub-systems (PLCs and NI PXI interfaces to sensors) were upgraded from the prior OPC-DA to the more secure OPC-UA protocol. Cryo-system PLCs were updated to allow Ganni cycle floating pressure calculations from any cold box to be sent to any compressor. During the project, the team recreated over 70,000 live data points, 50000 historical data points, and 4000 alarms. Finally, the graphical interfaces were upgraded to support HTML 5 in conjunction shared pages were implemented reducing the total number of webpages by over 75%
These system updates reinvigorated the previous SCADA system which had reached its end of life. The same look and feel was maintained while providing operators with an updated interface to control, troubleshoot, and record. The new system architecture is more robust and easier to maintain creating a path forward to address remaining problem points and implement additional features.
In the process of isothermal demagnetization of the adiabatic demagnetization refrigerator, the proportional–integral–derivative controller (PID controller) is often used to control the temperature stability and achieve the optimal response by adjusting the control parameters (proportional term Kp, integral term Ki, derivative term Kd). However, the manual tuning of the PID control parameters in experiments is very time-consuming and the tuning efficiency is rather poor. A numerical simulation model is thus very useful to guide the selection of PID parameters. In this paper, the third stage CPA salt pill of a three-stage adiabatic demagnetization refrigerator is taken as an example, and the adiabatic demagnetization process and the ensuing isothermal demagnetization process at 100mK are simulated using COMSOL software. By integrating the PID control model, the simulation results show how the dynamic response varies with the control parameters Kp, Ki, and Kd, which provides a valuable reference for the selection of PID control parameters in the experiments. Some experimental results and their comparison with simulation results are also introduced.
The ZEA-1 cryostat is a setup to enable experiments with liquid hydrogen in a closed cycle. The cryostat has a modular design so that it can be adapted to specific needs. The cryostat is used, among other things, to provide liquid hydrogen for neutron moderators. Therefore, the cryostat must be operated where neutrons can be provided, i.e. where there are either nuclear reactors or spallation sources. The modular structure, the different requirements of the experiments and the Europe-wide use place high demands on the measurement and control technology of the cryostat. Therefor it must be modular and flexibly expandable, enable the integration of different software, adaptable to on-site conditions and transportable, i.e. the hardware must be small, modular and light weight.
Our system architecture is based on the fact that the measurement and control signals are digitized and networked as close as possible to the sensor/actuator using the Ethernet standard (IEEE 802.3), which is available worldwide, reliably and cost-effectively using standard components. We use MQTT as network protocol, either in a closed LAN or encrypted in a WAN. A workstation or even a thin client is operated on site and not a large electrical control cabinet. Depending on the demands a MQTT server, a database management system specifically for time series, a control software and analysis and visualization tools are hosted at the workstation. To reduce the hardware furthermore, assuming a stable network, everything can also be hosted in the cloud, whereby at least a second MQTT server and a redundant control application should be operated in the local network, depending on the security requirements. Either an external time server or a (redundant) local, GPS-supported module is used for the time synchronization of the devices which can be done either via Network Time Protocol or via MQTT. Our approach is based on freely available software under an open source license. The software and hardware components we develop at the ZEA-1 are published in open access papers whenever possible. In addition to the advantages already mentioned, the reduction in computer hardware offers cost savings and, above all, energy savings, since thin clients and cloud-based computing can be used.
There is a Rare isotope Accelerator complex for ON–line experiments (RAON), which is a heavy ion superconducting linear accelerator, in South Korea. The RAON Control System uses Experimental Physics and Industrial Control System (EPICS), that is known as distributed soft real-time control systems for scientific instruments. The cryogenic system is comprised of many devices and actuators from different manufacturers and all them installed accelerator area where a radiation controlled area, it is difficult for engineer to access to the area due to the distance restrictions and radiation. We have developed a control system for cryogenic distribution system which is based on EPICS, remotely check the status of actuators and control them at the same time by using CS-Studio. This paper describes the Control system for cryogenic distribution system, and shows the loop test result.
The cool-down logic and the control system for the cryogenic distribution system of RAON Superconducting Linac 3 (SCL3) are described. SCL3 consists of 55 CMs, including 22 quarter wave resonant (QWR) type and 33 half wave resonant (HWR) type CMs, a helium distribution box (DBx), and an end box (EBx). In order to control thousands of actuators, an automatic control system is constructed to control the operation sequence and apply the protection logic. The flow of the operation modes and the operation sequence in each operation mode are designed with consideration of the system structure, the request of the cryogenic system, and the cryogenic fluid properties. The most important tasks during the cool-down process of the superconducting cavities are to shorten the cool-down time during the temperature range of 150 K to 50 K and to keep the steady and low pressure inside the cavities. The cool-down strategy of the cryo-modules (CMs) has been tested in the test facility and applied to SCL3 of RAON. The corresponding cool-down data are presented and analyzed.
The Climate change is the major challenge of this century. Thus, a carbon neutral and sustainable transportation sector could significantly reduce CO2-emissions and help to limit the global warming to a maximum of 1.5 degrees Celsius. For Siemens AG electric machines are a key technology to reach this ambitious goal. In combination with green hydrogen and fuel cells different areas of transportation such as aircrafts, ships, trains and trucks can be decarbonized. To improve the efficiency of electric machines or in special applications the power density, innovative designs and manufacturing methods are required. Therefore, additive manufacturing methods and hybrid materials are used to extend the freedom in design space and create improved electromagnetic parts and high-performance heat exchangers. To further increase the power density of electric machines up to 10 kW/kg a dual use of liquid hydrogen as energy storage and as cooling liquid is investigated. In the German S&G-Project “AdHyBau” a consortium of five partners investigates Additive Manufacturing methods and hybrid-materials in cryogenic environment and transfer these results to electric drive trains.
This paper presents a seamlessly integrated design- and simulation process for electric machines with high power density. Within this process we use numerical methods to create innovative solutions for coils and structural parts in a cryogenic environment of a hydrogen-hybrid electric drive train for vehicles such as ships, airplanes or trains. Some of these parts are built up as demonstrator and tested under laboratory conditions to validate the simulation process with experimental data.
Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904A.
Liquid hydrogen is in the spotlight as a versatile, clean, and safe energy carrier that is used, among other things, as a fuel in fuel cells and as a feedstock in the industrial sector. To safely transport and use liquid hydrogen, sophisticated cryogenic infrastructures, loading bays, loading arms, and vacuum-insulated transfer lines with the appropriate couplings, are required. Demaco has been at the forefront of the engineering, production, and installation of these systems for many years. An overview of some of the most prestigious hydrogen projects worldwide for marine, production, and distribution applications of liquid hydrogen will be addressed including their technical requirements and challenges.
Spatial homogeneity of critical current, Ic, is one of the most important practical performances of REBCO coated conductors. Continuous magnetization measurement by use of Hall-probe array is now widely adopted for the study of longitudinal Ic homogeneity in commercial REBCO tapes. However, the measurement condition is generally limited at 77 K and at around self-field (or low magnetic fields), while the practical operation conditions of the wires are much wider including higher magnetic fields and lower temperature. In this study, we have carried out in-field continuous Ic measurements of a long REBCO tapes not only at 77 K but also at 4.2 K, and have studied the correlation between Ic at 77 K self-field and that of various conditions including in-fields and 4.2 K. The high throughput measurements allow us to study these correlations based on many data points. Our results show that the positional variation of Ic is scaled independent of the conditions of temperature or external magnetic fields if we normalize the Ic value by the spatial average at each operation condition. This indicates that the spatial variation of the local Ic is dominated by the variation of effective cross-section area due to macroscopic defects and/or thickness- or width-variation whereas the flux pinning nature controlled by nano-scale defects is almost uniform along the longitudinal position in macroscopic scale. Namely, this suggests stable reproducibility of the nano-structure obtained by the PLD process.
Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP19H05617.
Chemical solution deposition (CSD) is a very competitive cost-effective deposition technique which has been used to obtain nanocomposite REBCO films and CCs, however their growth rates is rather small (0.5-1 nm/s) when the BaF2 route is used. To address this challenge, we have developed a novel growth approach, entitled Transient Liquid Assisted Growth (TLAG) [1], which is able to combine CSD of non-fluorine precursors with ultrahigh growth rates mediated by a non-equilibrium transient liquid (100-1000 nm/s), being compatible with nanocomposite structures including BaMO3 (M=Zr, Hf) nanoparticles [2,3]. High critical current densities have been achieved up of 5 MA/cm2 at 77K in thin films and the process has been transferred to thicker films and metallic substrates. In this presentation, we will discuss on the careful selection of non-fluorine solutions and nanoparticle synthesis to keep the nanoscale homogeneity of the film precursors [4]. In-situ analysis of the growth process by synchrotron radiation XRD and resistivity experiments has been crucial tools to pinpoint the kinetics aspects of this non-equilibrium process [1,3,5]. We also correlate the nanostructure of these films investigated by transmission electron microscopy with the vortex pinning landscape studied by the magnetic field, temperature and angular dependences measurements of the critical currents [1,6].
We acknowledge funding from EU ULTRASUPERTAPE (ERC_AdG-2014-669504) and IMPACT (PoC-2020) projects, from MCIU/AEI/FEDER for SUPERENERTECH (PID2021-127297OB-C21) and the Excellence Program Severo Ochoa (CEX2019-000917-S).
[1] L. Soler et al, Nature Communications,11, 344 (2020)
[2] S. Rasi et al, J. Phys. Chem. C, 124, 15574 (2020)
[3] A. Queraltó et al, ACS Appl. Mater. Interfaces, 13, 9101 (2021)
[4] L. Saltarelli et al, ACS Appl Materials and Interfaces, 14, 48582 (2022)
[5] S. Rasi et al, Advance Science, 9, 2203834 (2022)
[6] A. Stangl et al., Sci. Rep., 11, 8176 (2021)
REBCO coated conductors have gained significant attention in diverse areas in recent years due to their potential applications across a wide range of temperatures (4.2-77K) and magnetic fields (0-20T or higher). However, the persistent lack of characterization techniques to rapidly and reliably obtain information on the in-field performance of long length tapes remains a challenge. In this work, we evaluate the use of scanning Raman spectroscopy for characterizing long lengths of REBCO coated conductor tapes, as it can provide detailed insight into structure, composition, and local variations arising from defects or strain. We generate 2D maps of Raman wavelength and intensity features over extended lengths of conductor and correlate them to the information collected by reel-to-reel (R2R) 2D X-Ray Diffraction (2D-XRD) and R2R Scanning Hall Probe Microscopy (SHPM). The three methods are compared in terms of depth of information, detectability of variation in features of interest and the potential for evaluating critical current performance over a range of fields and temperatures. We also present an ongoing development of a R2R scanning Raman system and the technical aspects considered to achieve practicality, data reliability and speed.
REBCO coated conductors are increasingly of interest for high field magnets applications such as high field insert magnets for particle accelerator and fusion magnets. One promising design for such applications is the no-insulation magnet which utilizes the self-protecting mechanism of current sharing between REBCO tapes to provide better stability and quench protection to the coil. Our previous study has demonstrated that current sharing between REBCO tapes can be assisted by modifying the contact surface properties, inter-strand electrical contact resistance (ICR) and inter-strand thermal resistance (ITR), and one of the most effective methods through our study is Ni-plating that can give an inter-strand contact efficiency, η (η=ICRcontact area), of 2.7 μΩcm2. In addition, some novel designs of REBCO coated conductor tape/cable, for example STAR cable and tape with asymmetric Cu stabilizer, have suggested less percentage of Cu is included in the conductor structures, suggesting a less significant role of Cu in the conductor. Hence, in this study, we proposed to replace the Cu stabilizer with Ni to enhance current sharing between conductors. We used a Gamry cell to perform the electrolytic process of Cu removal and Ni plating. Then Jc of the Ni-plated tape was tested at 77 K under self-field and at 4.2 K under a background field ranging from 1 T to 10 T. The results were compared to the original tape. Then FEM analyses were performed with COMSOL Multiphysics to study the current sharing behavior in both the Ni-plated tape and the original tape to figure out how much improvement could be achieved by replacing the Cu stabilizer with Ni stabilizer.
High temperature superconducting (HTS) materials are increasingly of interest for high field magnets applications such as high field insert magnets for particle accelerator and fusion magnets. Symmetric Tape Round (STAR) wire cable has shown outstanding performance in current carrying ability, and therefore becomes a promising materials candidate for high field applications. On the other hand, the high magnetization and flux creep in HTS conductors can lead to a substantial time-varying error field during magnet operation. Hence, it is important to know these quantities so that the error field can be corrected or compensated during magnet design. In this study, we measured the magnetization and flux creep of a STAR cable through a 12-T magnet system. The sample was measured from -4 T to 8 T at a sweeping rate of 3.77 mT/s, and we extracted magnetization and penetration field based on the measured M-H loop. For flux creep analyses focused on the injection field region (< 1T). We performed five different field sequences, (1) 0 – 4 T – 0 – 1 T – Hold for 1800 s, (2) 0 – 4 T – 0.8 T – 1 T – Hold for 1800 s, (3) 0 – 4 T – 0.6 T – 1 T – Hold for 1800 s, (4) 0 – 4 T – 0.4 T – 1 T – Hold for 1800 s, (5) 0 – 4 T – 0.2 T – 1 T – Hold for 1800 s. The measured results, both magnetization and flux creep, were compared with a CORC cable that was studied by our group through a similar approach.
In order to study and control epitaxial growth of dissimilar materials, molecular beam epitaxial growth has been combined with scanning tunneling microscopy and spectroscopy (STM/S) and angle resolved photoelectron spectroscopy (ARPES) allowing both the structural and electronic properties to be investigated at the atomic scale. This presentation emphasize the formation of epitaxial topological materials on III-V semiconductor surfaces.
The electrically and thermally driven magneto-transport in two-dimensional frustrated spin systems reveals several fascinating features of correlated electron physics in magnetic Weyl semimetals. Here we present our measurements of anomalous Hall resistivity and Nernst voltage in Kagome spin lattices of Mn3Sn and Co3Sn2S2 epitaxial films prepared by multi-target magnetron sputtering. While the electron transport data for Mn3Sn films reveal distinct transitions through three different spin orders on cooling from ambient temperature, a layered ferromagnetic state emerges in Co3Sn2S2 in the vicinity of 150 K. The measured large zero-field Hall conductivity and Nernst effect in these compounds are finger prints of spin chirality driven transport. The details of these results along with the measurements of anisotropic magnetoresistance in these systems will be presented at the conference.
This research has been conducted at the United States Department of Defense Center of Excellence for Advanced Electro-photonics with 2D materials – Morgan State University, under the grant #W911NF2120213 and also funded by the AFOSR through grant #FA7550-22-1-0392.
Recent years have seen multiple high-throughput studies reveal an immense number of topological materials through use of symmetry indicators. Despite this success, three-dimensional topological insulators (TIs) admitting a band-gap larger than Bi2Se3 and two-dimensional TIs admitting a band gap larger than β-bismuthene, two of the originally proposed TIs, remain extremely rare, creating a bottleneck for progress in experiments and quantum devices. Simultaneously, a significant effort has been made to understand and identify topological phases “invisible” to symmetry indicators. Such phases offer a unique opportunity to expand the search for a large band-gap TI, however their identification requires sophisticated probes of bulk topology. Magnetic flux tubes or vortices have emerged as one such probe in two-dimensions when inserted into the bulk. In this work, we develop an automated workflow to perform vortex insertion and apply it to a current database of high- quality, experimentally realized, two-dimensional insulators. The results reveal multiple novel two- dimensional topological insulators supporting large bands gaps, including the 1H-MX2 (M=Mo,W) and (X=S,Se,Te) family of transition metal dichalcogenides. Our work has broad implications for current theoretical and experimental efforts to employ these materials in superconducting and Moire systems.
We have been investigating whether mixing organic olefin-based thermosetting dicyclopentadiene (DCP) resin, commercially available as TELENE by RIMTEC Corporation in Japan, with high heat capacity ceramic powders, increases the specific heat (Cp) of impregnated Nb3Sn superconducting magnets. This is ongoing as the international scientific collaboration between U.S. and Japan. Using a high Cp resin as impregnation material for Nb3Sn magnets is expected to considerably increase the specific heat of the superconducting coil package when compared with standard impregnation epoxies (CTD-101k). This novel technology will contribute to reducing Nb3Sn superconducting magnet training at a minimum cost. The high Cp resins in this study were fabricated by a combination of a ceramics powder filler and TELENE. TELENE is typically cured by the use of an additive, which is the ruthenium complex. The curing time is controlled by the amount of retardant. The powder filler is selected among high heat capacity ceramics, such as Gd2O3, Gd2O2S, and HoCu2. These powder fillers are mixed with the TELENE by using a planetary mixer. The viscosity, heat capacity, thermal conductivity, and other physical properties of TELENE with powder fillers were measured in this study. In addition, we investigated the effect on the bending mechanical property of those resins after gamma-ray irradiation. Moreover, we used TELENE to impregnate the Nb3Sn short undulator magnet made at Argonne National Laboratory. These results will be also reported in this paper
A part of this study is supported by U.S.-Japan Science and Technology Cooperation Program in High Energy Physics operated by MEXT in Japan and DOE in U.S.
The high-cycle fatigue properties of ASME standard XM-19 (ASTM A240) austenitic stainless steels (22Cr-12Ni-(Mn, Mo, Nb, V, N), in mass%) have been examined at 77 K. The steel is strengthened by nitrogen solid-solution and grain refinement with (Nb,V) precipitates, and shows the advantages of high strength at cryogenic temperature and excellent weldability. In this study, the fatigue strength of the steel has been evaluated, and influence of microstructure on the fatigue strength is discussed.
The 30-mm-thick hot-rolled plate was solution-treated at 1373 K. The plate in a square of 30 mm bars was cold-groove-rolled to a rectangular bar in a square of 14.3 mm and was annealed at 1173 K (partial recrystallization, PR), 1273 K (fine recrystallization, FR) and 1373 K (solution-treated, ST) for 3.6 ks, followed by air cooled. Their average grain sizes were 3.3 μm (PR), 8.9 μm (FR), and 42.5 μm (ST), respectively. The test specimens were taken from the bars parallel to the rolling direction. Load-controlled fatigue tests were carried out at 77 K (immersed in liquid nitrogen). The sinusoidal waveform loading is uniaxial with a minimum-to-maximum stress ratio of R=0.01 and frequencies of 10 Hz.
The fatigue crack initiation site shifted from the specimen surface to the specimen interior in the longer-life range. In the ST material, the sharp drop in fatigue strength over 10⁶ cycles was related to subsurface crack initiation failure. Both the PR and FR materials showed considerably improved high-cycle fatigue strength at 77 K, while the increase in the fatigue strength in the low-cycle regime was almost proportional to the increase of their tensile strength.
Effective reinforcement materials require both a high value for tensile strength and a high modulus of elasticity in order to provide a high capacity for load bearing and a high resistance to deformation under external force. At cryogenic temperatures, both strength and modulus are usually amplified. For applications, properties at both temperatures have to be characterized. We have investigated a nickel based alloy. This alloy has higher Young’s modulus than stainless steels, which have been used as reinforcement materials at cryogenic environment. The test materials have been subjected to thermo-mechanical processing that strengthens the alloys through very fine planar defects. We studied property changes resulting from deformation in the alloys at either cryogenic or room temperature conditions. At cryogenic temperatures, the alloy had more resistance to plastic deformation than at room temperatures. We also investigated physical property changes at cryogenic temperatures and magnetic fields. This presentation summarizes the properties of this alloy and its microstructure under various conditions.
Acknowledgements
This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida.
Ultrahigh conductivity Al (Al hyperconductors, RRR ~10^4) can be considered as an alternative to superconductors for cryogenic AC applications e.g. in the stators of electric aircraft fan motors. Such conductors can be much better than normal state wires, and competitive with superconductors in certain frequency bands. On the other hand, the low yield strength of such a material renders a conductor difficult to manufacture and unsuitable for magnet applications. To offset the low yield strength, the pure Al can be reinforced by bonding it to a high-strength alloy. In past work, the alloys Al-8Fe4Ce (RRR ~ 17) and Al-4Fe2Ce were selected which have the needed strength and will not contaminate the pure Al. However, an applied magnetic field to the alloy conductor can degrade the RRR to an extent quantified by anomalous magnetoresistance. In this effect, A transport current, I, is divided between the core and the sheath in the inverse ratio of their resistances; the core current is dominant and in the presence of an applied field, B, produces a Hall voltage VH which drives a current along the sheath and dissipates power. In this work, we design a high-purity aluminum strand with a high-resistivity matrix material, Cu-30Ni, and measure its contributions to anomalous magnetoresistance using PPMS temperatures down to 4K in fields up to 12T and compare its results to analytical calculations and modeling with FEM.
Suborbital aerospace, orbital, and lunar power distribution networks are desiring lightweight electrical conductors. Cryogenic hyperconducting aluminum (99.9999%+ pure) is a competitive option to HTS cables at lower temperatures below 20 K due to its high RRR, but hyperconducting aluminum cables require mechanical reinforcement for many applications, reducing current density, and this strengthening must be compatible with aluminum’s annealing schedule to prevent impurity diffusion. AlBeMet 162 is a lightweight Al-Be nanocomposite which can be processed like aerospace structural grade aluminum alloys, and like hyperconducting aluminum, does not experience the extreme quench characteristics seen in superconducting composites. In this research, we shall present the electrical conductivity of cryogenic AlBeMet 162, and compare its mass specific engineering current carrying capacity under variable cooling conditions with high RRR copper, hyperconducting aluminum composites, nano carbon metal composites, and a high current density REBCO coated conductor. The electrical conductivity will be examined as a function of magnetic field up to 3 T to examine magnetoresistance and possible anomalous magnetoresistance. The possibility of AlBeMet 162 as a lightweight and low AC loss Litz conductor will also be presented versus the newest low-loss BSCCO and MgB2 composites and high RRR Cu and Al litz. It will be shown that AlBeMet 162H is a superior DC electrical conductor for aerospace in the temperature range of 80 to 150 K and AlBeMet 162H serves a place in the discussion for new low AC-loss conductors.
We investigated the microstructures achievable by severe plastic deformation processing of copper-tantalum powder composites with a Ta volume fraction ranging from 0.25 to 0.75 by sintering. Additional composites of the same tantalum content were prepared with a minor addition of titanium, added to facilitate interphase bonding. The sintered composites were extruded via several ECAE routes, and the resulting microstructures characterized by scanning electron microscopy (SEM) and hardness and tensile testing. The Ti modification was found to markedly improve the strength and extrudability of the composite allowing fabrication of copper-tantalum composites with novel microstructures. The Ti addition apparently causes solid solution softening of the Ta phase and enables the Cu and Ta phase regions to uniformly co-deform.
For the green energy transition, the transport of large amounts of electrical energy is needed both in densely populated areas and over long distances. Superconducting power cables represent one possible solution, requiring energy-efficient liquid nitrogen re-cooling stations for an economical operation at cable lengths longer than about 1 km to 2 km.
In this contribution, a model for simulating cryogenic mixed-refrigerant cycles (CMRC) based on the Joule-Thomson effect and an associated optimization algorithm are presented. The distinctive feature of CMRC is the combination of good scalability of the cooling capacity, adaptability of the mixture to the specific application and an inexpensive process design. While the process is relatively simple, the identification of ideal operating conditions and mixture compositions requires complex modelling. In order to optimize these characteristics for CMRC processes, the Differential Evolution algorithm is adapted to a model built in Mathematica. Thermodynamic property data is calculated with the Peng-Robinson Equation of State as part of CoolProp, an open-source thermophysical property library. First simulation results are presented and further improvements are being discussed.
The Brayton Circulating Cooling System is a unique refrigeration system developed as a technology demonstration for providing cold helium gas refrigeration at high pressures to an external superconducting magnet or any remote load for cool down purposes. The system is designed to provide cool down refrigeration from room temperature to target minimum temperatures of approximately 40K.
The system consists of an F-70H helium compressor with gas control manifold, interconnecting gas lines, cables, the Brayton refrigeration unit mounted in a Dewar assembly and a control system. Electricity, cooling water for the compressor and a source of helium (99.995%) for make-up gas are the only required utilities. The prototype achieved 1300W at 291K and minimum temperature of 56K when measured with an external heat load simulator. The scope of the project, system design, target specifications and summary of test results will be discussed in this paper.
Cryogenic expanders are complex and expensive components in recuperative-cycle cryocoolers. To simplify cryogenic expander technology, we propose a novel acoustic expander. The acoustic expander utilizes sound waves in the expansion process without the need for complex moving parts at low-temperature; in contrast to turbine or piston expanders that require spinning shafts or moving displacers at low-temperature. This work models the operation of the acoustic expander and presents preliminary experiments that verify its function.
Recent helium shortages and helium price increases have lead to an increased emphasis being placed on conserving helium. The need to conserve helium must be balanced with need to maintain the high levels of purity necessary to prevent operational problems caused by contamination. Helium losses and contamination control are especially important for test stands that have cryogenic distribution systems operating continuously with frequent changeover of cryogenic temperature components that are being tested. This paper describes a mathematical model to estimate the quantity of helium lost and the purity of the helium after the pump and backfill procedure is complete. The process to determine the optimal time during pump down to cut off pumping and start backfilling is described. There is a tradeoff between trying to achieve the lowest possible pressure during pumping and the quantity of air leaking into the volume while pumping is occurring. An additional benefit of careful selection of pump and backfill parameters in conjunction with real-time pressure monitoring can reduce the labor and time required to complete a successful pump and backfill procedure. This paper is intended to be a tool for engineers to review their pump and backfill procedures and measured data to optimize helium losses, system purity, and labor required.
Oak Ridge National Laboratory, through support of the US Department of Energy’s Office of Basic Energy Sciences, has begun applying machine learning methods to improve accelerator and target performance of the Spallation Neutron Source (SNS). One application of these methods is the control optimization and power upgrade of the Cryogenic Moderator System (CMS). To study such optimizations and system modifications, a digital twin of the CMS has been developed using EcosimPro. This tool was developed to numerical model continuous-discrete systems, has functional mockup interface and unit (FMI-FMU) model connectivity, and a validated library of cryogenic components for dynamic system numerical simulations. This effort discusses steady state and transient validation of numerical results from the digital twin with experimental data. Control optimization studies were performed and focused on dampening mass flow, temperature, and pressure fluctuations during sudden losses of energy input from the SNS accelerator during beam trips. This was achieved by adjusting five decentralized proportional-integral-derivative controllers connected to four flow control valves and one electric heater. Future efforts include power uprate studies focused on increasing cooling capacity of the CMS to accept more energy input by the SNS accelerator. The current accelerator beam power is 1.4 MW and upgrades to 2.0 MW to first target station are underway are part of the Proton Power Upgrade effort. The cooling capacity of the system is sufficient for 2.0 MW operation.
The European Spallation Source ERIC (ESS) will provide long-pulsed cold and thermal neutron fluxes at very high brightness to the research community. At the ESS target, high energy spallation neutrons are produced by impinging a 5 MW proton beam on the high-Z material, tungsten. The proton beam is pulsed with a repetition of 14 Hz and a pulse length of 2.86 ms. The spallation neutrons are moderated to cold and thermal energies by the moderators. In the beginning, the ESS will install two hydrogen moderators, which have been designed and optimized to achieve a maximum neutron brightness under the condition of parahydrogen fraction higher than 99.5%. The current plan is to replace them with four (two above and two below the target wheel, respectively) in the future. A cryogenic moderator system (CMS) has been designed to continuously supply subcooled liquid hydrogen with a temperature of 17.5 K and a parahydrogen fraction of more than 99.5% to the two moderators placed in parallel and to maintain an average temperature rise at the moderators within 3 K. The liquid hydrogen will be circulated at the flow rate of 0.5 kg/s for the two moderators (1 kg/s for the four moderators in the future) by two centrifugal pumps in series. The CMS is cooled through a plate-fin type heat exchanger (HX-1) by a 20 K large-scale helium refrigeration plant with a maximum cooling capacity of 30.3 kW at 15 K. The author developed a simulation code for the J-PARC CMS, which could predict the dynamic behaviors of the temperature fluctuation caused by the proton beam switching on or off for 300 and 500-kW proton beam operations. In this study, a one-dimensional simulation code has been developed in order to understand the temperature behaviors and the pressure distribution during the ESS CMS cool down process based on the code for J-PARC. The CMS cooldown process was divided into three phases (I: vapor state, II: condensation state and III: liquid state). The cooldown process analysis has been performed and the operational methods and parameters such as cooldown speed, pump speed and valve positions have been optimized. It was verified that the CMS would be able to be cooled down to the nominal condition within 27 hours.
The cryogenic distribution system at FRIB is extensive, encompassing three Linac segments, fourteen experimental system superconducting magnets, cross-connect between FRIB and the reconfigured NSCL legacy system, and the A1900 magnets, as well as many other user experimental loads. The cool-down or warm-up of these transfer-lines is an inherently transient process and must be conducted at a gradual enough rate to keep local temperature gradients and corresponding thermal stress on the piping system within acceptable limits. To this end, estimation of this transient process is very helpful in operational planning. Two different models were developed to capture the transient characteristics of the cool-down (or warm-up) process with a real fluid properties, and considering the effects of heat in-leak, momentum, flow resistance, and piping components. The first model employs a Crank-Nicolson implicit method, while the second model uses a MacCormack explicit method. Computational cost of the proposed models were compared, and results were validated against a simple closed-form solution. Each model was then employed to estimate the cool-down of FRIB transfer line sections, and were compared to previously obtained experimental data. This paper discusses the advantages and disadvantages of each numerical method for this model, as well as their accuracy compared to the actual transfer-line.
Dalian Advanced Light source (DALS) test facility program will build four testbenches, a horizontal test bench (HTB) for module testing, a vertical test bench (VTB) for superconducting cavity testing, an injector test bench (ITB) for beam testing and a cryogenic test bench (CTB). The testbenches cooling are provided by a 370 W @ 2 K cryoplant. The simulation of the cryogenic system can play an important role in the development, commissioning and operation of the cryogenic system, such as process calculations, control logic optimization and building operating training system. This report is based on the Ecosimpro software to build a dynamic simulation model of the DALS cryoplant, including the compressor system and key components in the cold box, most of the control loops of the cryoplant are established in this model. The simulation is carried out to study the cooldown process of the cryoplant and the operating conditions in each operating mode.This model provides the guidance for the subsequent commissioning of the cryoplant and lay the foundation for the simulation of the distribution system.
Fermilab is involved in superconducting accelerator magnet R&D under the framework of the U.S. Magnet Development Program (USMDP). An integral part of that program is High Temperature Superconducting (HTS) accelerator magnet development to demonstrate self-fields of 5 T or greater compatible with operation in hybrid LTS/HTS configuration to generate fields beyond 16 T for future High Energy Physics (HEP) applications.
To address the ever-increasing requirements on the magnetic field strength from the physics community, which lead to exorbitant levels of mechanical stresses in the coils and degradation of conductor properties, Fermilab is developing the Conductor on Molded Barrel (COMB) magnet technology. It offers an elegant solution for fabrication of dipole, quadrupole and higher-pole coils with round conductors, offering stress management and precise turn positioning to enhance the magnetic field quality.
The COMB magnet technology couples well with Symmetric Tape Round (STAR®) wires produced by AMPeers LLC, which are amongst the most promising REBCO conductors for future HEP applications. Due to the proprietary architecture placing the superconducting layer near the neutral plane of the tape, they offer unrivaled bending performance suitable for magnets with the bore size in 50-60 mm range, which will be needed for future HEP experiments.
This paper reports progress in the development of COMB magnet technology with STAR® wires. A two-layer dipole magnet with 60 mm clear bore has been recently fabricated and tested in liquid nitrogen. The purpose of the test was to determine what kind of critical current degradation occurs in the process of winding the STAR® wire into the COMB structure.
The reported magnet development efforts include design of the coil and the support structure with the magnetic and structural analyses, short sample studies to assess the critical current degradation due to conductor bending in the coil end regions, as well as the magnet fabrication and testing.
*This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program. This work was supported by U.S. Department of Energy Office of Science, Office of High Energy Physics SBIR award DE-SC0022900.
The Electron Ion Collider (EIC) Hadron Storage Ring (HSR) will reuse most of the existing superconducting magnets from the RHIC storage ring. However, the existing stripline beam position monitors (BPM) used for RHIC will not be compatible with the planned EIC hadron beam parameters that include higher intensity, shorter bunches, and some operational scenarios with large radial offsets of the beam in the vacuum chamber. To address these challenges, the existing RHIC stripline BPMs will be shielded, and a new BPM design using button pick-ups was integrated into a new vacuum interconnect/bellows assembly that will be installed adjacent to the existing BPMs.
A dedicated analysis of the new BPM housing and button pick-up design has been conducted to assess the thermal effects caused by beam induced resistive wall heating. Also, this analysis was extended to determine the heating from the BPM signal propagation through the cryogenic cables, for several operational scenarios. This paper reports on the analysis results to quantify the heat transfer and temperature distribution that can be expected on the new HSR cryogenic BPM housing, button pick-ups, and cables.
Fermilab’s Illinois Accelerator Research Center (IARC) is designing small-scale, ~10 MeV prototype conduction cooled superconducting accelerators for projects ranging from medical device sterilization to road pavement modification. These accelerators are built using high-Q Nb3Sn coated superconducting radio-frequency cavities. The cryostat design for one such prototype being developed for the U.S. Army Engineer Research Development Center (ERDC) will be described. Cryostats for such conduction cooled accelerators require stringent control of thermal losses since the available power from cryocoolers is restricted to a few watts. The present state of the vacuum vessel, conduction cooling system, thermal shield, cavity support, and other ancillary system designs will be described as well as presentation of thermal and structural simulations. The results of this paper will lead to the engineering construction of a cryostat which will accelerate an electron beam to high energy, ~10 MeV, with extremely low thermal losses.
The experiments described and the resulting data presented herein, unless otherwise noted, were funded under PE 0603119A, Project B03 "Accelerator Technology for Ground Maneuver", managed by the U.S. Army Engineer Research and Development Center. The work described in this presentation was conducted at Fermilab. Permission was granted by Fermilab and ERDC to publish this information.
Superconducting undulators with a period >15 mm can offer a much higher on-axis undulator field than state-of-the-art cryogenic permanent magnet undulators with the same period and vacuum gap. The commissioned NbTi planar SCUs for user operation in the KIT synchrotron and the APS storage ring are operated stably without quenches, producing outperformed photon flux in the high energy part of the hard x-ray spectrum. Another potential advantage of deploying SCU is its radiation hardness, a crucial characteristic for being used in free electron lasers (FELs) driven by high repetition rate superconducting linear accelerators (LINACs) and diffraction limited storage rings (DLSRs) with small vacuum gap and large averaged beam current. The development of shorter period but high field SCU is an important mission for compact FEL as this technology would reduce both the length of undulators and the length of LINACs. This presentation will first overview the research and development of SCUs worldwide from the late 1970s to 2022 and the technical challenges including the SCU cryostat, the magnetic field measurement and the integral/local field correction. Then we compare the theory limits of different types of planar and helical SCUs and summarize the technological needs for future undulators, e.g. made of coated-conductor or bulk HTS materials.
To enable the design of future in-space cryogenic propellant vehicles such as Lunar and Martian ascent and descent stages and the nuclear thermal propulsion system, high accuracy models of various phases of the propellant transfer process are required. NASA and US universities are developing and validating numerical modeling tools that can be used for future in-space cryogenic system design and analysis. The limiting challenge has been the lack of direct-cryogenic data at the relevant scale and environment; thus the current suite of models is predominately anchored to ground tests with cryogens and/or simulant fluids in reduced gravity. In collaboration between NASA Glenn and Case Western Reserve University across two projects, this presentation covers recent computational fluid dynamics (CFD) simulations of different elements of the cryogenic propellant transfer process using commercial software FLUENT. The CFD simulations in reduced gravity for line chilldown are the first of its kind to be anchored to direct-cryogenic data taken in a reduced gravity environment. This presentation will cover an overview of the validation experiments, CFD model set up, and CFD model results.
Keywords: cryogenic propellant transfer, microgravity, CFD, line chilldown, flow boiling
Large cryogenic systems, like those installed at CERN, are complex systems relying on many diverse physical processes and phenomena that are difficult to simulate and monitor in detail. With only a limited number of properties measured and made available for monitoring and control purposes, several processes contributing to the dynamics of the systems are ignored and therefore reduce the accuracy and capability of the model to track, predict and anticipate. Accurate analytical or numerical computer modelling can be developed to simulate the non-linear dynamics of the processes but are complex, computationally intensive, and cumbersome to test, validate and implement with different configurations and limited measurements of the hidden properties.
In this work, we are presenting our investigation of using Graph Neural Networks (GNN) to build a model of the helium II bayonet heat exchanger operating in the LHC at CERN.
GNNs are artificial neural networks for processing data that can be represented in terms of graphs and have recently become quite popular in the High-Energy Physics field because of reduced computational cost and generalisation capabilities.
We are proposing to use a hybrid machine learning approach, where the parameters of the GNN model are estimated by a combination of supervised learning algorithms trained on experimental data and bounding physics equations and parameters.
The GNN model was initially trained on data from the experiments performed on the LHC prototype magnet Strings and validated on data extracted during the operation of the LHC machine.
We demonstrate the model accuracy, repeatability, and robustness in various configurations. The model is also well inspectable and explainable providing the time evolution of all variables.
We report on the results and expected application for predictive control, diagnostic and operators training as well as its extension to other systems to obtain a global cryogenic system model.
Efficient storage of cryogenics fluids (CFs) under microgravity environment requires detailed quantification of interfacial thermodynamics and mass transport. Such mechanistic understanding will provide strategies to mitigate boil-offs in presence of non-condensable (NC) gases and to engineer novel storage approaches. While several continuum models are being employed for this purpose, they lack the resolution to predict the nanoscale phenomena at the vapor-liquid interface and often depend on parameterized description of the interfacial thermodynamics and transport. In this work, we use molecular dynamics (MD) simulations to predict the interfacial transport and thermodynamics of CFs in presence of NC gases with the aim to (i) derive mechanistic understanding of the nanoscale process and (ii) validate the underlying assumptions used in developing the continuum models and quantify properties of interests to develop relevant correlations. These correlations can be typically incorporated into the continuum models thereby integrating critical information across length scales that are necessary for optimizing CF storage. Specifically, we focus on liquid nitrogen (LN2) and liquid oxygen (LO2) as model CFs. Neon was modeled as the NCs gas to predict the CF-NC interactions at the vapor-liquid interface (the Knudsen layer). We show that, the NC gas preferentially adsorb at the Knudsen layer impeding the condensation of the CF, thereby leading to boil-offs. Finally, we also discuss potential molecular descriptors that can be used for tuning the interfacial condensation rates and to mitigate boil-off.
Accurate modeling of cryogenic boiling heat transfer is vital for the development of extended-duration space missions. Such missions may require the transfer of cryogenic propellants from in-space storage depots or the cooling of nuclear reactors. Purdue University in collaboration with NASA has assembled a database of cryogenic flow boiling data points from heated-tube experiments dating back to 1959, which has been used to develop new flow boiling correlations specifically for cryogens. Computational models of several of these experiments have been constructed in the Generalized Fluid System Simulation Program (GFSSP), a network flow code developed at NASA’s Marshall Space Flight Center. The new Purdue-developed correlations cover the full boiling curve: onset of nucleate boiling, nucleate boiling, critical heat flux, and film boiling. These correlations have been coded into GFSSP user subroutines. The fluids modeled are nitrogen and methane. Predictions of wall temperature and heat transfer coefficient are presented and compared to the test data.
Mixed-refrigerants are desired for near ambient temperature refrigeration and cryogenic cooling systems, to obtain enhanced cooling performances, relative to pure refrigerants, and to comply with new global environmental regulations. Therefore, the vapor-liquid equilibrium (VLE) of light hydrocarbon mixtures is numerically studied by solving the Rachford-Rice flash equations, based on the Peng-Robinson equation of state and the van der Waals mixing rules. In a previous research, the method has been validated against experimental results of several mixtures, and it is published elsewhere. The VLE of a mixture is the most basic data which is required for determining new refrigerants.
The main advantage of the presented method, relative to many other methods for calculating VLE of multi-component systems, is the fact that it doesn’t involve numerical iterations. As a results, the presented method doesn’t have convergence problems, it is fast, and therefore, it allows extensive investigations of different mixture compositions at various pressures and temperatures. The method allows generating VLE diagrams either at a constant pressure or at a constant temperature, for binary mixtures, and phase diagram of ternary mixtures at given pressure and temperature. The method also enables to calculate a specific VLE state of mixtures with any number of components, at any pressure and temperature.
In the current research we investigate binary and ternary mixed-refrigerants for Joule-Thomson cryocoolers, aiming for cryogenic cooling applications at temperatures between 80 and 180 K. Numerous mixtures were investigated, consisting of nitrogen, argon, methane, ethane, propane, n-butane, n-pentane, and carbon dioxide. The presented mixtures are the most interesting mixtures, which provide relatively high coefficient of performances (COPs). The COP is defined as the ratio between the cooling power and the compression work. The cooling power is determined by the isothermal Joule-Thomson effect, and the compression work is the adiabatic compression work, between the operating pressures. In order to reduce the number of degrees of freedom in this complex research question, and to focus on available compressors, a fixed pressure ratio of eight is maintained in the current research.
A vast majority of the items made in the modern world are dependent on materials sourced through mining operations. The world uses mining to obtain the materials needed for shelter, transportation, and more, including steel, solar panels, and electronics. Not only does mining contribute to the global consumer market, but the industry also provides employment to millions of people, with over 13.6 million people employed worldwide in 2016 [1]. A large portion of the mines lie within the Pacific Rim, which contains many rich mineral deposits.
Unfortunately, while the economic contributions of the mining industry are large, so are its contributions to global warming. Mining contributes 4–7% of annual global greenhouse-gas emissions [2]. Diesel fuel alone accounts for about 50% of mining-related CO2 emissions. Governments around the world are pushing to lower CO2 emissions and advocating for a transition across industries to clean energy. To meet these goals, the global transition to clean energy will require unprecedented extraction of raw materials, most of which will be obtained through mining. Therefore, mining cannot be discarded, and it must transition to clean energy as well. Heavy industry is often ignored and underfunded when it comes to identifying innovative and reliable pathways to decarbonization. However, a transition is occurring, and mining companies are beginning to make pledges to reduce emissions, with hydrogen fuels, particularly liquid hydrogen, emerging as a key method of addressing the emissions problem. By decarbonizing mining haul fleets and transitioning trucks away from diesel, there is an opportunity to reduce carbon emissions by 50% or more at any given mine site.
Founded in Seattle, Washington, USA, First Mode is a global decarbonization company committed to seizing this opportunity by working to help heavy industry, starting with mining, transition to a diesel-free future. On May 6, 2022, First Mode debuted the world’s largest hybrid hydrogen and battery powerplant, replacing the diesel engine in a Komatsu 930E-4 ultra-class haul truck at Anglo American’s Platinum Group Metals mine site at Mogalakwena, South Africa. First Mode is now refining the design of the powerplant and developing support infrastructure. The resulting system will be produced and adopted at scale, starting with a retrofit of approximately 400 ultra-class haul trucks for Anglo American. To support this development effort, First Mode has established a proving ground at Centralia, Washington. The site is a retired coal mine (now in reclamation) and moving forward it will be used to test the next generation of hydrogen-fueled ultra-class haul trucks, as well as the associated hydrogen refueling infrastructure, within a true mining environment.
Growing the hydrogen fuel economy has the potential to revolutionize heavy industry, lowering emissions while creating new economic opportunities. However, simply changing the fuel source will not eliminate emissions. To fully transition fleets away from diesel, additional changes must be made in parallel, including addressing change management, establishing a fuel supply chain, and providing education to enable safe operation. Fully embracing this transition within heavy industry will benefit areas affected by mining, not only in the Pacific Rim, but across the globe as well.
[1] World mining employment for selected countries 1/ world mining ... [Internet]. National Mining Association; [cited 2023Feb9]. Available from: https://nma.org/wp-content/uploads/2016/12/m_world_employ.pdf
[2] Delevingne L, Glazener W, Grégoir L, Henderson K. Climate risk and decarbonization: What every mining CEO needs to know [Internet]. McKinsey & Company. McKinsey & Company; 2021 [cited 2023Feb8]. Available from: https://www.mckinsey.com/capabilities/sustainability/our-insights/climate-risk-and-decarbonization-what-every-mining-ceo-needs-to-know
The Bipartisan Infrastructure Law has significantly increased the opportunity to use hydrogen as an alternative energy carrier and energy storage medium. However, doing so requires the development of safe and efficient storage vessels, delivery systems, and distribution infrastructure. Cryogenic liquid hydrogen and cryo-compressed gaseous hydrogen are considered high energy density alternatives to ambient temperature gaseous hydrogen but have unique engineering challenges in addition to the typical hydrogen compatibility issues. Cryo-compressed hydrogen requires pressures exceeding 700 bar to achieve higher energy densities, which necessitates extreme material strength requirements. On the other hand, liquid hydrogen systems face extreme environmental demands of including temperature cycles over a 300 K range and to as low as 20 K. It is common to use austenic stainless steels and composite overwrapped metallic vessels for liquid hydrogen and cryocompressed systems, respectively. However, such common materials have rarely been studied at these cryogenic temperatures with hydrogen exposure. In this study, various cooling and pressurization profiles simulating cryocrompressed tank refueling cycles illustrate stress development in metal liner and composite overwrap components. . This study will also illustrate the hydrogen and cryogenic effects on 304L and Nitronic 50 alloys and their welds, and how the effect of composite fiber surface treatments can influence the short-beam shear behavior at temperatures as low as 20K. While lower temperature is known to increase strength properties and reduced elongation at fracture, the presence of internal hydrogen increased both strength and elongation at fracture, but reduced ductility as measured by reduced cross-sectional area. Magnetic evaluation of the uniformly strained region of the test specimens suggests that hydrogen mitigates the strain-induced transformation to α’-martensite. Brittle fracture features and secondary cracking indicative of hydrogen embrittlement were observed on the fracture surfaces of hydrogen-precharged specimens, which is consistent with the loss of ductility
The sustainability of the energy sector is becoming increasingly important in the face of ongoing climate change. Given the rapid growth rate of the aviation industry, it is imperative to decarbonize aircraft propulsion in order to meet the goals set forth by the Air Transport Action Group (ATAG) of a 50% reduction in $CO_2$ aircraft emissions by 2050 compared to 2005 levels. Hydrogen propulsion is considered the most viable technology to achieve this target, with the demand that short to mid-range hydrogen aircraft will be operational by 2035. To facilitate this swift development, an efficient development and transition process must be established.
A key enabling technology component for the implementation of hydrogen aviation is the hydrogen storage. For this application the gravimetric storage density, which refers to the energy content per unit mass of the entire storage vessel, is particularly important. To meet the gravimetric storage density requirements of medium to long-range aircraft, hydrogen must be stored cryogenically. The construction material is a crucial factor that affects the overall vessel mass. Utilizing carbon fibre reinforced polymers (CFRP) instead of metals allows for a reduction in tank mass and offers improved material resistance against degradation due to hydrogen.
Composite materials allow for a multitude of parameters in design, material, and manufacturing to be tailored for the specific use case. These advantages result in a high degree of freedom in geometry and design of cryogenic hydrogen vessels. Albeit composite materials exhibit complex interacting failure modes, such as delamination, matrix microcracking and fibre failure, potentially leading to a system hazard, depending on the severity and the type of failure mode. These mechanisms depend on the design, material, and manufacturing parameters and are also affected by the environmental conditions that may influence the material properties or introduce overloads. Complex interactions and interdependencies lead to significant uncertainties within the design process, resulting in high safety margins and therefore low gravimetric efficiency of the cryogenic hydrogen vessel.
The proposed article introduces a novel approach for the systematisation and analysis of potential failure mechanisms and interactions across length scales of the cryogenic composite vessel based on the Fault Tree method. Initially, the boundary conditions of the system are defined. A hierarchical system model, spanning across the length scales from the overall cryogenic vessel at the system level to individual components such as liner, inner/outer shell, insulation, and balance of plant components, and further down to the element level of the composite material and the micro-material level, is established. The environmental conditions considered include mechanical, thermal, medial and radiation loads in flight operation.
Subsequently, potential failure mechanisms of the cryogenic composite hydrogen vessel are systematised across the length scales. Typically, failures originate from phenomena at the micro-material level, like residual stress or degradation of mechanical properties, triggered by external loads or manufacturing defects. With a certain probability, these phenomena result in the initiation of a failure at the micro-material level, which may then propagate throughout the various length scales up to the system level. This approach provides a means of analytically evaluating the failure probabilities of the entire cryogenic composite hydrogen vessel, considering both structural failure modes and their interactions, as well as functional failure modes of specific components, such as valves. This enhanced insight into the failure mechanisms, their propagation throughout the length scales of the system and the impact of external influences facilitates the derivation of requirements for system design, material, manufacturing and testing. As a result, this enables an efficient development process, while significantly reducing the uncertainties of the cryogenic composite hydrogen vessel and enhancing the gravimetric efficiency without compromising safety.
Acknowledgements: The authors thank the Boysen-TU Dresden-Research Training Group for the financial support that has made this publication possible. The Research Training Group is co-financed by Technische Universität Dresden and the Friedrich and Elisabeth Boysen Foundation.
The dielectric strength of insulating materials was studied under shear stress to evaluate the insulation performance of rectangular conductor coils for fusion reactor. Particular attention was paid to the problem of insulating properties under stress.
In this study, dielectric strength of glass cloth reinforced epoxy under shear stress was measured at room and liquid nitrogen temperature. For the measurement of dielectric strength, first, a dielectric strength test was performed in the parallel to the reinforcement cloth. The sample geometry is a double-notch shear specimen. By compressing the specimen, the inter-laminar shear failure was induced. The dielectric strength in the parallel to the reinforcements was measured by digging holes from both sides of the sample and the insulation strength of the remaining thickness was measured. The reason for digging the holes is to reduce the dielectric breakdown voltage and to prevent creeping discharge. The dielectric strength was measured under the shear stress by compressing the specimen.
In this direction, the growth rate of the mechanical defect was fast, and the crack was introduced from the bottom of the notch, leading to total fracture almost simultaneously. This is because the cracks propagate through the inter-laminar region in this mechanical tests. Concerning the dielectric strength, we have observed that the dielectric strength began to reduce at lower stresses than macroscopic mechanical defects (visually detectable defects) were introduced. The phenomenon was observed not only at room temperature but also at liquid nitrogen temperature. Examination of the discharge path revealed that the discharge path was along the yarn. It was considered that the discharge path was formed by connecting micro-cracks at the interface between the glass filament and the resin accompanying the deformation of the yarn.
A similar test was performed in the direction perpendicular to the reinforcements. Mechanical tests in this direction showed serrations where the stress decreased with the introduction of matrix cracks. This is because the mechanical test in this direction requires the cracks to travel across the reinforcement cloth. The breakdown voltage decreased due to the introduction of cracks into the matrix or subsequent crack opening due to stress. Even if dielectric breakdown occurs, the sample did not lead to the total mechanical destruction. This is because the fibers withstand the stress even if the matrix cracks were introduced.
These phenomena mean that the dielectric withstand voltage of the insulating material is lowered by external stress. The stress level where the dielectric withstand voltage begins to decrease is lower than the mechanical breaking stress of the insulating material. These phenomena could be considered to provide a notion for the insulation design of fusion superconducting magnets.
This work was supported by QST Research Collaboration for Fusion DEMO.
Keywords: insulating materials, glass fiber reinforced plastic, dielectric strength under shear stress.
Hydrogen is expected to be one of the most promising energy options for future energy generation as it is renewable, is environmentally friendly, and has high gravimetric energy density. Hydrogen can be stored in the form of compressed gas, in materials such as metal hydrides, and in liquid phase. The most efficient way to transport and store hydrogen is in the liquid phase. Moreover, compared to other storage methods, liquid hydrogen (LH2) has significant advantages in terms of energy density and safety. However, owing to the extremely large temperature gradient between LH2 and the environment, heat ingress into the LH2 tanks inevitably occurs, causing evaporation loss. Thus, a special type of insulation system is required to reduce the evaporation loss and the properties of insulation materials for cost-effective insulation systems for stationary applications and offshore transportation need to be analyzed. Although the design code requires the testing of various material properties for the intended service temperature, the performance analysis of insulation materials is performed between the normal boiling temperature of liquid nitrogen (77 K) and ambient temperature (298 K), which is the minimum temperature range in the design code. To evaluate the insulation performance, a thermally guarded horizontal cylinder is developed that advantageously comprises a demountable outer cylinder to easily adapt various types of insulation materials. The main components of the test bed are as follows: (1) inner cylinder (testing cylinder), for which insulation materials are installed and evaluated, (2) guard cylinders, which minimize the heat ingress from both sides of the inner cylinder, (3) vacuum pump system, which can control the degree of vacuum in the annular space up to 10−5 torr, and (4) sensors (temperature, vacuum, and mass flow) and DAQ. The heat flux, temperature distribution, and effective thermal conductivity from the mass flow rate of liquid nitrogen are measured using the boil-off calorimeter method. The results are compared to the effective thermal conductivity data obtained by NASA to prove the reliability of the proposed test bed. To evaluate the mechanical properties of the insulation materials, special types of jigs are fabricated considering the type (bulk, mat, and powder) of insulation material. A custom-built cryogenic chamber with a universal testing machine is used to maintain the temperature during the mechanical test, and the internal temperature is maintained using liquid nitrogen, which can reduce the temperature to 77 K. The materials tested include multi-layer insulation, powder insulation (glass bubble), aerogel blanket, and spray-on foam insulation, which are candidate materials for LH2 tanks. To consider transient effects, such as the sudden loss of vacuum in a vacuum-jacketed annular space, thermal performance data are obtained for the full cold vacuum pressure range (from 5 × 10−6 torr to 760 torr). Furthermore, the thermal performance of different combinations, such as spray-on foam/multi-layer insulation and aerogel blanket/multi-layer insulation, is measured to compare the theoretically and experimentally obtained values.
Acknowledgments
This work was supported by the Development and Demonstration of Eco-friendly Ocean Clean-up Vessel (RS-2022-00143968, Development and Demonstration of Eco-friendly Ocean Clean-up Vessel) funded by the Ministry of Trade, Industry & Energy(MOTIE, Korea). This work was supported by the Technology Innovation Program (20018917, Performance verification of Mock-up considering operating environment of vessel and cargo containment system) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).
Due to the strict emission restriction standards for fossil fuels, hydrogen has great promise as a future ecofriendly fuel. It is the most abundant chemical element in the universe, and hydrogen energy production emits no greenhouse emissions. However, since hydrogen is the lightest element, large-volume storage tanks are required to realize the same fuel efficiency as fossil fuels. Hydrogen can be stored in gaseous, liquid, and solid forms (metal hydrides). However, in terms of the storage efficiency, liquid hydrogen is the most suitable. Moreover, since the risk of explosion of liquid hydrogen is significantly lower than that of high-pressure tanks, it can be employed for storage and transportation applications. Liquid hydrogen storage tanks require an effective insulation system to prevent heat ingress from the outside. Therefore, unlike conventional LNG, all heat transfer mechanisms, i.e., conduction, convection, and radiation, need to be blocked in liquid hydrogen storage tanks. Particularly, since liquid hydrogen has a lower boiling point and a lower density and latent heat of vaporization than LNG, even a small heat ingress may cause significant loss. For liquid hydrogen storage tanks, the design of its insulation system is an important influencing factor, and their performance depends on the filler and protective materials employed for the vacuum insulation system. The performance of existing insulation materials is evaluated in terms of thermal conductivity, but the performance of vacuum insulation systems is difficult to similarly evaluate. Therefore, effective thermal conductivity, which reflects both convection and radiation, is used as a performance index. Effective thermal conductivity is a material property that is calculated based on the heat flux and financial resources of the measuring equipment when no dominant heat transfer mechanism is present. The cryogenic thermal property data of the liquid hydrogen fuel tank insulation system have been measured by NASA for rocket propulsion. The apparatus used in the cryogenic insulation test has been reported in two technical standards of ASTM International: C1774 and C740. However, the standards recommend using 77 K liquid nitrogen as the test fluid. In this study, the advanced cryogenic insulation test apparatus and methods with 4 K liquid helium are investigated. The facility comprises two helium chambers (test and guard chambers), and the heat ingress is blocked using MLI vacuum insulation and liquid nitrogen shield to minimize the helium loss. For verification, the obtained results are compared with the data reported by NASA, and the insulation performance of powder materials (such as glass bubble and perlite) suitable for the insulation system of the current large-capacity liquid hydrogen storage vessel is evaluated. Furthermore, to evaluate the powder material insulation system, a sample container is separately manufactured and a special material filter is used.
Acknowledgments
This work was supported by the Development and Demonstration of Eco-friendly Ocean Clean-up Vessel (RS-2022-00143968, Development and Demonstration of Eco-friendly Ocean Clean-up Vessel) funded by the Ministry of Trade, Industry & Energy(MOTIE, Korea). This work was supported by the Technology Innovation Program (20018917, Performance verification of Mock-up considering operating environment of vessel and cargo containment system) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).
Non-vacuum insulation systems are frequently applied in the thermal management of low temperature systems as well as for the use and storage of cryogens. Aerogels are known for their low density, high mesoporosity, high surface areas, low thermal conductivity and high acoustic impedance. This study focuses on polymeric aerogels that can be mass produced as large monoliths while maintaining the low thermal conductivity over a wide temperature range. The manufacturing flexibility of polymeric aerogels allows fabrication of monolithic blocks and sheets that can be applied in various configurations to insulate cryogenic and superconducting devices. To measure the thermal conductivity, an immersion calorimeter was developed and has been operated at different cold boundary temperatures. The calorimeter heats a hollow cylinder of insulating material on the inside surface and the surrounding bath maintains a cold boundary. This calorimeter was used to measure the thermal conductivity of commercially available FoamGlass and a hollow cylinder of a polymeric aerogel machined from a cast cylinder. The thermal conductivity of the FoamGlass and the polymeric aerogel are compared at room temperature (290 K), ice bath (273 K), and liquid nitrogen (80 K) cold boundary temperatures. Room temperature measurements of the modulus of elasticity and yield strength using an optical technique are also reported for flat specimens of the aerogel made from the same stock as the cylindrical specimens tested for thermal conductivity.
Recent developments in high temperature superconducting (HTS) cables have allowed for reductions in conductor diameter. For electric transport applications operating voltages required for HTS cables range from 1-10 kV. The reduction in conductor diameter represents higher electric fields on the surface of the conductor. Based on the electrical insulation strategy employed for the HTS cables there is also the potential for further electric field enhancement if the electrical insulation is not directly bonded to the HTS conductor or ground layer. In this instance the cryogen becomes part of the electrical insulation which can effect the dielectric integrity of the cable.
As part of our strategy to reduce electric field enhancement we have studied cryogenic epoxies as a technique to enable direct bonding with the conductor to reduce electric field enhancement. As part of our continued research we have focused on techniques to directly apply the ground layer to the electrical insulation utilizing either conductive epoxies or paints.
The paper discusses the partial discharge behaviors of various small scale samples measured at 77K in high purity vacuum, pressurized helium gas, and liquid nitrogen. The dielectric measurements enable the feasibility of the various conductive epoxies and paints as the ground layer of HTS cables to be assessed. The paper also provides electric field analysis to show where electric field enhancement has been reduced with these techniques.
The AC conduction of superconducting heterostructures of SmB6/YB6 are investigated via time domain terahertz spectroscopy[1]. A two-channel model of thickness-dependent bulk states and thickness-independent surface states accurately describes the measured conductance of bare SmB6 thin films, demonstrating the presence of surface states in SmB6. While the observed reductions in the simultaneously-measured superconducting gap, transition temperature, and superfluid density of SmB6/YB6 heterostructures relative to bare YB6 indicate the penetration of proximity-induced superconductivity into the SmB6 overlayer; the corresponding SmB6-thickness independence between different heterostructures indicates that the induced superconductivity is predominantly confined to the interface surface state of the SmB6.Our results show that SmB6 behaves as a predominantly insulating bulk surrounded by conducting surface states in both the normal and induced-superconducting states in both terahertz and DC responses, which is consistent with the topological Kondo insulator picture. In the second part, I will present the observation of a gapless superconducting state in Fe(Te,Se) epitaxial thin films and in Fe(Te,Se) heterostructures with Bi2Te3 and MnTe grown by hybrid symmetry epitaxy. Clear 1/ω behavior arises in the imaginary conductance below the superconducting transition; however, there is no concomitant suppression of the real conductance, indicating a gapless superconducting state. Furthermore, a sharp, low-frequency peak in the real conductance emerges alongside the superconductivity. We model these anomalous features of the superconducting state to determine the origin of this novel behavior.
References:[1] Phys. Rev. Lett. 130, 096901 (2023).
In this work, we report unconventional superconducting properties of high quality Au(111)/Nb heterostructure samples. We carry out tunneling studies in Au(111) using planar tunneling devices with a highly transparent barrier, which enhances the energy resolution of tunneling spectroscopy and allows us to observe and analyze fine in-gap states. We show a locally enhanced Zeeman field due to a large Landé g-factor at the barrier/Au(111) interface, and a broken of Pauli limit at the surface of Au(111) while maintaining bulk superconductivity. We will also show tunneling results along nanowires of magnetic insulators coupled to Au(111). Our work paves the way for searching and confirming robust topological superconductivity in the Au(111) platform.
We developed a stepping motor working in a cryogenic environment with small heat dissipation from it. While a cryogenic motor is commercially available, a user must prepare a cryogenic environment that can tolerate a large heat dump during the operation.
We modified a commercial stepping motor (TAMAGAWA SEIKI CO., LTD) for room temperature usage. The components of the motor were replaced from a conventional electromagnetic wire to 6N high-purity copper and from aluminum chassis to a glass-fiber resign epoxy chassis. The former reduces the Joule heat, and the latter reduces the eddy current. In addition, the bearings have been replaced with ones with a dry lubricant. An iron yoke, a stack of iron core plates, is already introduced in the commercial motor to reduce an eddy current loss, and this was kept from the commercial design.
The preliminary experiment was conducted at teh temperature of 15 K using a GM cryocooler to estimate the heat dissipation on the motor. The results show that the electrical resistance of the high-purity copper wire at 15 K is 1950 times lower than at room temperature. We measured the total heat dissipation of the motor with the high-purity copper coils and compared it to the conventional one. The measured heat dissipation was reduced by about 40% when the motor rotation speed was 2.25 rpm. The Joule loss of the motor with a high-purity copper wire was about 1/20 smaller than the conventional motor due to the reduction of the wire resistance. We also identify that the remaining heat dissipation is dominated by the component proportional to the rotational frequency, i.e. hysteresis or static friction from the bearing.
This development was motivated by using a cryogenic stepping motor in a cryogenics space mission with limited active and passive cooling power.
Over the last twelve years, Gloyer-Taylor Laboratories (GTL) has been developing and testing a series of ultra-lightweight composite cryogenic propellant tanks in a range of sizes (16” dia to 63” dia) and form factors (cylinders and spheres). These cryotanks have been validated to deliver 75% mass reduction compared to equivalent state-of-the-art cryotanks.
For example, GTL’s 48” dia x 96” long composite cryotank [83.1 cu ft, 26.6 lb (44.3 lb with skirt extensions), Weight/volume = 0.32 lb/ft3 tank only] remained leak-tight through 18 cryo-thermal pressure cycles with liquid nitrogen with 7,500 micro-strain in the cylinder section and showed no sign of degradation from testing.
While GTL initially focused on launch vehicle and spacecraft applications using liquid oxygen (LOX) and liquid methane (LCH4), recently GTL expanded our efforts to include liquid hydrogen (LH2) for emerging hydrogen electric aircraft and LH2 space vehicles. GTL is now developing all-composite, vacuum-jacketed, LH2 dewar-tanks that provide hydrogen weight fractions in the 60% to 80% range including composite dewar shell, multilayer insulation, and inner tank.
In this paper, GTL will provide an overview of GTL’s composite cryotank development efforts and associated testing.
The demand for highly efficient chill-down technologies for transfer lines and storage tanks of cryogenic propellant systems in future space mission has intensified in recent years. To ensure successful and reliable operation of the propellant system, it is necessary to achieve high liquid loading in the tanks, which requires a vapor-free flow in the transfer line. The high temperature difference between cryogenic fluid and its surroundings, however, leads to valuable propellant loss due to boil-off. To minimize this loss, a chill-down process is required to cool the transfer line to a desired cryogenic temperature. The line chill-down process is characterized by unsteady two-phase flow, which occurs sequentially in three distinct regimes: vapor film boiling, transition boiling and nucleate boiling regime. The chill-down process is overwhelmingly dominated by the less efficient vapor film boiling regime, in which a vapor film separates a liquid core from the wall. Therefore, the key to achieving a faster chill-down and minimizing propellant usage is promoting the fast transition from the vapor film boiling to the transition boiling regime.
Heat transfer augmentation techniques can be simply classified into two types: passive and active methods. Active techniques require additional external power to operate, whereas passive techniques involve modifications to the system configuration, such as extended or specially treated surface, inserts, and porous materials, etc., to enhance heat transfer without the additional external power. In aerospace applications, where power saving and maintenance are crucial factors, passive methods are more suitable than active ones. Among the various types of passive techniques, wire coil inserts are known for their excellent design flexibility. Wire coils can be an optimal solution for achieving efficient chill-down, especially considering the wide variability of propellant transfer line configuration and mass flow rate across different systems and their operating scenario.
This study aims to examine the effectiveness of wire coil inserts in enhancing the heat transfer of cryogenic transfer lines for rapid chill-down. Liquid nitrogen (LN2) is used as a test fluid and circular cross-sectioned wire coil inserts with five different pitch-to-diameter ratios (p/D = 0.47, 0.75, 0.93, 1.12, 1.40) are explored. The chill-down experiment is conducted for stainless steel tube in vertical orientation under various mass flow rates. The experimental apparatus comprises a liquid supply section, test section, and vaporizing section. The thermodynamic state of the fluid is monitored in the liquid supply section to ensure that the liquid-phase fluid flows into the test section. In the test section, a test tube is insulated using foam rubber to minimize parasitic heat in-leak from the ambient environment. Temperatures are measured at multiple locations along the tube wall using E-type thermocouples for thermal characterization, while pressures at the inlet and outlet of the test section are measured for pressure drop calculation. It has been experimentally observed that the wire coil inserts cause a substantial enhancement in chill-down efficiency and in turn significantly reduce the chilldown time by more than 1/5 in comparison to the smooth tubes. This is achieved by promoting mixing and breaking down the vapor film, and thereby facilitating the transition from the vapor film boiling to the transition boiling regime. This finding is of significant importance as it suggests a fast chill-down method that can effectively reduce the chill-down time for various systems with different configuration and mass flow rates.
Acknowledgement
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2022R1F1A107133711).
In the application of infrared detectors, pulse tube cryocoolers are required to provide cooling power at different temperature ranges simultaneously with light weight and compact construction. Generally, each pulse tube cryocooler can provide cooling power in a certain temperature range with only one cooled sink that is the cold-end heat exchanger. In this paper, a single stage pulse tube cryocooler is designed to provide cooling capacity at different temperature ranges with an extra cooled sink placed in the middle of the regenerator. The axial distribution of volume flow and pressure wave of cryocoolers with middle heat exchanger and without middle heat exchanger are compared theoretically. To verify the simulation results, a series of experiments were also carried out. As a result, the cooling power of cryocoolers with middle exchanger was decreased at 80K, and 0.5W @ 88.5K & 0.5W @ 195.8K cooling capacity was obtained simultaneously at 45W input power.
A micro coaxial pulse tube cryocooler has been developed for infrared detection by Key Laboratory of Technology on Space Energy Conversion, CAS. It has a tiny size and high frequency, driving by the linear compressor, and using the combination of inertance tube and buffer as phase shifter. At present, the operating frequency of this pulse tube cryocooler is 175Hz - 215 Hz, and it can provide a cooling power of 0.3 W - 0.5 W at 80 K with an input electric power of 30 W at 300 K reject temperature. This paper presents the performance tests data and describes the design and optimization process of this micro coaxial pulse tube cryocooler in detail.
A high-efficiency single-stage coaxial pulse tube cryocooler operating at around 35K has been developed for long wavelength infrared detectors. The design considerations are presented, and with the cryocooler model of the Sage, the optimizations on the length of regenerator are described. By experimentally investigation, the cooler prototype has achieved a no-load temperature of 24K, with an inertance tube and reservoir as the phase-shifter. By further adding the double-inlet to the phase-shifter, a lower temperature of 21K can be achieved. At present, the cooler prototype has a typically cooling performance of 2W at 35K with 200W input power at the frequency of 37Hz. Besides, the key parameters and performance of the designed PTC are presented at details.
The gas film between the thrust disc of rotor and the thrust gas bearing in the axial direction is only tens of microns in the small-type cryogenic turbo expander. The rotor was suspended under the action of the gas film pressure to rotate frictionlessly at high speed. The bearing loading capacity is one of the static characteristics of small-type turbo expander, experimental research in the study of static characteristics is more important than numerical simulation, a new and accurate type of test system for dynamic measurement of axial thrust bearing loading capacity of small-type turbo expander is presented in this paper. The system can accurately measure the gas film force between the thrust disc and the thrust bearing, study the influence of different structural parameters on the bearing loading capacity, and simultaneously monitor the dynamic relationship between the gas film force and the value of film gap.
The Johnson Space Center’s Space Environment Simulation Lab (SESL) has both Chamber A, the world’s largest purpose-built thermal vacuum chamber capable of creating deep space conditions, and Chamber B, the largest human rated thermal vacuum chamber. A unique design feature of these chambers is the gaseous helium cryopumping panels within the liquid nitrogen shroud. This shroud is used to bring the chamber to cryogenic temperatures while the cryopumping panels trap gasses using their large surface area in order to create a high vacuum environment of 5*10^-6 Torr. In preparation for the James Webb Space Telescope (JWST) flight test, a series of functionals required the chamber to run at higher temperatures, and therefore did not need active cooling from the liquid nitrogen shroud. During testing, cryopumping panels were used to mitigate contamination during this main shroud warm-up. One of the cryopumping panels in Chamber A was covered with several layers of aluminized mylar in order to thermally protect the zone from the warmed shroud. This strategy was effective and became part of operations during JWST testing. Currently, Chamber B has requests for both commercial and NASA space suit tests at both high and low temperatures to accurately generate thermal models. High temperature tests would greatly benefit from simultaneous shroud warming and the high vacuum environment provided by the cryopumping panels. This paper will quantitatively define the thermal loads on the panels used in previous Chamber A warm up sequences. Additionally, this report will perform a thermal analysis to judge the feasibility of adding layers of aluminized mylar to the cryopumping panels of Chamber B.
Cooling performance in positive displacement cryocoolers is dependent on the relationship between the compressor’s displacement and the cold head’s displacement. An experimental investigation explored the relationship between compressor and cold end displacement for a single-stage gas-driven GM-type cold head operated at different frequencies. As loss mechanisms can be frequency related, the investigation also compared varying the cold end displacement by changing stroke length instead of changing operating frequency. Results showing these relationships are presented, and their impact on seal wear and variable-speed operation are discussed.
The NMR magnet is cooled by two kinds of cryogens. The boil-off rate of the cryogen in a general NMR magnet is 20 cc/h for liquid helium and 200 cc/h for liquid nitrogen. We have developed a zero boil-off system that can greatly suppress the evaporation of liquid helium and liquid nitrogen.
This system is equipped with a GM cryocooler, with a nitrogen cooling chamber on the 1st stage and a helium cooling chamber on the 2nd stage. Since NMR measurement is sensitive against external noise, each cooling chamber was connected to the NMR magnet using a flexible transfer tube to suppress the vibration of the magnet. The tube has a slope angle to generate efficient convection flow of gas and liquid.
This system was mounted on an NMR magnet, and it was confirmed that the noise generated by system vibration was at a level that would not interfere with NMR measurements. It has also maintained a stable zero boil-off for more than 6 months.
A cryogenic mixed refrigerant Joule-Thomson refrigerator was developed to apply the cryogenic etching process with non-flammable constituents. 2-stage cascade type mixed refrigerant Joule-Thomson refrigerator was analyzed to figure out the coefficient of performance of the refrigeration cycle. The working fluid of mixed refrigerant Joule-Thomson refrigerator is non-flammable mixture of argon(Ar), tetrafluoromethane(R14), trifluoromethane (R23) and octafluoropropane(R218). The designed refrigeration cycle was adapted to cool down the coolant of HFE7200 (Ethoxy-nonafluorobutane, C4F9OC2H5) with the target temperature of -100°C. Cooling capacity of 2 kW was obtained at the heat exchanger of the coolant side. The detailed experimental results of the mixed refrigerant Joule-Thomson refrigerator were discussed in this study.
A 4 K Helium Joule-Thomson (JT) refrigeration system based on ejector technology is presented in this paper to enhance the thermodynamic efficiency, which could also decrease the lowest cold head temperature and avoid higher suction pressure of the compressor. This paper studies the influence on the cryocooler performance of ejector parameters using one-dimension numerical simulation. A comprehensive system exergy analysis is also conducted and the loss of each component is analyzed. The performance chart of the JT refrigeration system with an ejector is established after calculation and compared with the system without an ejector, which indicates a 10-20% performance improvement.
With the global focus on energy and environmental issues, hydrogen energy development has become more and more important. The liquid hydrogen pump is an important equipment for hydrogen transportation, whose performance is significantly decided by the impeller. In this paper, we designed an integrated impeller with an inducer and an centrifugal impeller and optimized the axial length and outlet angle of the centrifugal impeller. Grid independence and cross validation prove that the simulation model and results are reliable. It is worth noting that a high roughness is given to the impeller surfaces in our simulation to obtain results closer to the real situation. By analyzing the pressure and relative liquid flow angle distribution in the fluid domain, the structural design of the impeller is optimized, and then the performance curve is obtained. At the same time, the cavitation phenomenon is analyzed.The simulation results will provide a guidance for the manufacture of our liquid hydrogen pump, and also provide a reference for the design and manufacture of other liquid hydrogen pumps.
Liquid hydrogen piston pump is the key equipment in the process of storage, transportation and refueling of liquid hydrogen. The timely motions of suction and discharge valves are beneficial to the transport performance and volumetric efficiency of the pump. This paper sets up an operation frame of liquid hydrogen piston pump in which reciprocating piston and check valves with conical spool interact. Backflow caused by lagging motion of spool is more likely to be observed in suction valves than in discharge valves. Based on the system simulation, the influence of spring stiffness, half-cone angle of conical spool and dead volume of compression chamber on suction valve’s backflow volume are analyzed. The results show that both increase of spring stiffness and decrease of half-cone angle of conical spool in the proper range can reduce the backflow volume at the suction valve. Increased dead volume allows backflow in the suction valve at the beginning and end of suction. The larger the dead volume, the smaller the rate of pressure change and the larger the backflow volume. This work helps to optimize the design parameters and improve the volumetric efficiency of the liquid hydrogen piston pump.
Compared with other off-site hydrogen refueling stations, the liquid hydrogen refueling stations have the advantages of high storage and transportation efficiency, good economy of medium and long-distance transportation, low construction investment and high hydrogen purity, which has become an inevitable trend in the development of hydrogen refueling stations in the future. The energy consumption of liquid hydrogen pump is much lower than that of compressor in high-pressure gas hydrogen refueling station, which is the key technical link for the development of the liquid hydrogen refueling station. However, there are few published data on the research of reciprocating liquid hydrogen piston pump, and its thermodynamic process is still unclear.
In this paper, the thermodynamic analysis of the high-pressure pressurization process of the reciprocating liquid hydrogen piston pump is carried out in view of the influencing factors such as the gas content of liquid hydrogen, the surrounding environment heat leakage, the piston friction loss and the liquid hydrogen evaporation loss in the working process of the reciprocating liquid hydrogen piston pump, and the main reasons affecting the efficiency of the reciprocating liquid hydrogen piston pump are calculated. The key technologies such as improving the efficiency of liquid hydrogen piston pumps, reducing cold capacity loss, and reusing cold energy were further discussed, and some suggestions were put forward for the development of liquid hydrogen piston pumps in the future.
At research institutes, liquid helium is commonly transferred to mobile dewar vessels via a single flow transfer line, driven by a pressure built up in the storage vessel. In this process, a considerable amount of the liquid evaporates according to the prevailing pressure drop and due to the heat leak into the transfer line. Further, the generated flash gas must undergo an energy intensive recovery and liquefaction procedure again. To significantly reduce these transfer losses, the cryogen can be transferred by a centrifugal pump to the target dewar. At the same time, the displaced cold gas is guided back to the storage dewar in a cold return line within the same insulated transfer housing. This article presents the current development status of the transfer system, including the thermo-hydraulic modeling and simulation.
Barber-Nichols has significant experience successfully applying induction motors in cryogenic fluid pumping applications between 100 and 4.2 Kelvin. These induction motors typically include metallic materials of silicon steel laminations, aluminum rotor bars, and copper windings. Barber-Nichols recently validated an analytical model for induction motor performance with dynamometer testing at ambient and liquid nitrogen temperatures. The test results support understanding of the electromagnetic behavior of these materials at cryogenic temperatures and the design and application of induction motors to rotating cryogenic machines. The findings are relevant and important to terrestrial and aerospace cryogenic systems where design validation by analysis and test are critical to achieving system performance objectives. Results and conclusions to be presented at the conference.
Excessive pressure drop will cause the liquid hydrogen vaporing when the liquid hydrogen flows through the inlet valve, resulting in a decrease in the volumetric efficiency of the reciprocating pump. In this paper, we will optimize the structure and inlet parameters of the inlet valve through numerical simulation to reduce the vaporization rate and improve the volumetric efficiency of the reciprocating pump.
The High Luminosity (HL-LHC) upgrade of the Large Hadron Collider at CERN is an example of large-scale international scientific cooperation which spans multiple international partners. Canada through TRIUMF is making an in-kind contribution to the project with the delivery of 5 crab cavity cryomodules. The cryomodules will be delivered to CERN by 2026 for installation in the LHC. TRIUMF will receive the RF dipole (RFD) crab cavities from a consortium of US labs. In preparation for the assembly of the cryomodules TRIUMF has undergone a number of upgrades. Chief among these is the preparation and commissioning of a new cryogenic insert for the TRIUMF multi-purpose cryostat to allow testing of the jacketed cavities at 2K. The insert consists of a heat exchanger and JT expansion valve. The 2K pumping power has been augmented from 20W to 40W with the addition of a booster sub-atmospheric pump. The details of the upgrade and results from commissioning will be reported .
PIP-II HB650 SRF cavities have a very ambitious performance specifications of achieving a Q factor of 3e+10. Each cavity must undergo vertical tests and demonstrate its performance before it can be qualified for assembly into a cryomodule. The vertical tests are conducted at 2 K, in very low residual magnetic field less than 0.5 uT. In order to expel magnetic field trapped inside the cavity it must be cooled at a very fast rate exceeding 20 K/min in the temperature range between 45 K and 4 K. This requires substantial modifications to the existing vertical test stand at Daresbury and to the associated cryogenic processes which must be tightly controlled. In this paper we describe the modifications to the system and processes developed to achieve the desired fast cool-down rates.
The HFVMTF (High Field Vertical Magnet Test Facility) is a new experimental facility under development at Fermi National Accelerator Laboratory (FNAL) to test large superconducting magnets (up to 20 tons weight and 1.3 m diameter) in a double bath superfluid helium cryostat (1.9 K and 1.2 bar). Coupled with a superconducting dipole magnet fabricated by Lawrence Berkeley National Laboratory (LBNL), this facility will be able to test future high-temperature superconductor (HTS) cables under a background magnetic field of 15 T for fusion magnets. This paper describes the design of the cryostat and its 1.4-meter diameter lambda plate, as well as the different components for a safe operation of the facility, even during critical events such a magnet quench or a vacuum breaking situation. The project is funded by US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES).
A new 20,000 liter (20 KL) liquid helium dewar is being integrated in to the existing cryogenic system at the Facility for Rare Isotope Beams at Michigan State University (MSU-FRIB). This dewar will serve a new planned cold box system that supports the large experimental system superconducting magnets and the many legacy superconducting magnets in the downstream beamline. This dewar has a single large penetration, or “neck”, that all the process lines and instrumentation pass through. On top of the “neck” is a vacuum insulated interface box, or “neck can”, which houses all the connections between the dewar and the connecting distribution system transfer-line. Though not generally common, this design approach has been successfully implemented on 5 to 10 KL liquid helium dewars at the Spallation Neutron Source (SNS), Jefferson Lab (JLab), and also at FRIB. It has been found that this approach greatly simplifies the mechanical design, while allowing for multiple process and instrumentation interfaces and still permitting a low heat in-leak. This paper presents an overview of the mechanical and process design of this new neck can.
A design for a 4.2 K cryostat to support superconducting undulator (SCU) magnets is being developed as part of an SCU free electron laser (FEL) technology demonstrator. An array of several cryostats will be installed as an afterburner at the end of the existing hard x-ray beam line of the LCLS-II facility at the SLAC National Accelerator Laboratory (SLAC). Cryostat requirements include high operational availability, precision positioning and measurement capability to support beam-based alignment, high undulator magnet packing fraction, operational transparency to the electron beam, and compatibility with the existing LCLS hardware and space constraints. A cryocooler-based refrigeration system is appropriate given the scale and operational profile of the demonstration. The design is being developed as part of a collaboration between SLAC and Argonne National Laboratory (ANL) and draws on ANL’s experience with SCUs at the Advanced Photon Source.
The Proton Improvement Plan-II (PIP-II) is a major upgrade to the Fermilab accelerator complex, featuring a new 800-MeV Superconducting Radio-Frequency (SRF) linear accelerator (LINAC) powering the accelerator complex to provide the world’s most intense high-energy neutrino beam. This paper describes the conversion of the PIP-II Injector Test Facility (PIP2IT) cryogenic system into a test stand for PIP2 High-Beta 650 MHz (HB650) cryomodules at Fermilab’s Cryomodule Test Facility (CMTF). A description of the associated mechanical, electrical, and controls modifications necessary for testing HB650 cryomodules are provided. The cooldown and warmup requirements, procedures and associated controls logic is described. The prototype HB650 static and dynamic heat load measurements are reported.
As one major part of heat transfer at cryogenic temperature, thermal radiation has an important impact on the design and operation of cryogenic systems, which is mainly related to the temperature and emissivity of the surface of material. Previous studies show that the surface roughness of material has an influence on the magnitude of the emissivity, which varies from different surface finishes. In this paper, oxygen-free copper and stainless steel which are commonly used in cryogenic systems are performed by different surface treatments. Emssivities of those metallic materials with different surface roughnesses are measured at cryogenic temperature, and the effect of metal surface structure on emissivity at different temperature are studied.
Epoxy resins have been widely employed as impregnating materials in high field superconducting magnets, due to their electrical insulation, high elastic modulus and strong bond ability. However, epoxy resins usually have a large coefficient of thermal expansion (CTE). When the epoxy-impregnated magnets are cooled to cryogenic temperature, thermal mismatch stresses will be generated in different materials, leading to the risk of structural failure. Reducing the CTE of epoxy and making it close to that of superconducting composite wire/tape will effectively restrain the thermal mismatch stress and thus reduce the risk of structural failure. In this study, the thermal expansion and mechanical properties of epoxy composites filled with negative thermal expansion zirconium tungstate (ZrW2O8) powder were investigated within the temperature range of 77–300 K. The experimental results showed that the CTE of the composite epoxy (CE) decreased with the increase of the volume fraction of ZrW2O8, especially when the volume fraction of ZrW2O8 was 40%, the CTE of the CE was close to that of REBCO coated conductors. In addition, with the increase of ZrW2O8 volume fraction, the equivalent elastic modulus of the CE increased, but the tensile strength increased to the maximum and then decreased. To further explain the mechanism, a numerical finite element model (FEM) of representative volume element of CE was established. The FEM results were in good agreement with the experimental data, which explained the mechanism of the decrease of CTE and the enhancement of mechanical properties in CE.
The advance in superconducting microdevice technologies over the past couple of decades has shown promise for practical applications of quantum computers and superconducting photon detectors for far-IR telescopes and optical communications. One of the key factors limiting the current technology lies in the small gap and limited kinetic inductance of superconducting materials being used. Magnesium diboride (MgB2) has the largest known gap – well above 1 THz – among metallic superconductors in ambient pressure, but has not been utilized due to the lack of wafer-scale films suitable for microdevice fabrication. Here we present high quality smooth MgB2 films on 4-inch Si wafers with high uniformity, roughness below 0.5 nm rms, and high kinetic inductance of 46 pH/sq. We have further developed mature fabrication processes for a large-area array of devices, and present results of these processes along with proof-of-concept prototypes.
The 1144 phase (Ae1A1Fe4As4) shows a strong advantage of engineering fabrication among Fe (Iron)-based superconductor (FBS) family due to the robustness of its superconducting properties with respect to chemical inhomogeneities, granted by its uniform crystalline-layered structure. This regularity is furthermore associated to crystalline defects capable of acting as efficient pinning centers, which high critical currents achieved at high fields for these superconductors. Like other FBS phases, its lossless current-carrying capability can be remarkably degraded by distractions at grain boundaries (GBs). GB oxidation is an issue of upmost importance to the realization of the practical FBS application for high field (> 20T) magnet. In this study, we explore oxidized grain boundary and intrinsic grain structural properties of 1144 polycrystalline samples by applying analytical electron microscopy such as atomic resolution scanning transmission electron microscopy and atom probe tomography. These structural properties of samples produced by a mechanochemically assisted synthesis are evaluated following the degradation of superconducting properties due to oxidation. We observe a strong correlation between the contamination at grain boundaries and the decrease of transport properties of the bulk sample, while the crystallin structure seems to be not affected by the oxidation.
Iron-based superconducting wires and tapes, particularly 122-type, based on the powder-in-tube method are promising for high-field magnet applications. A promising design is to use silver/copper composite as the sheath material (i.e., Ag is in direct contact with the IBS powder for minimum reaction while Cu is used as the outer matrix to reduce conductor cost and increase the mechanical strength). However, for this design a low heat treatment temperature must be used to reduce Cu/Ag interdiffusion or even formation of liquid, but such a temperature may be well below the optimum heat treatment temperature for the best Jc performance. To solve this issue, a bi-layer barrier design was developed, in which an Nb or Ta layer is inserted between Ag and Cu to prevent their inter-diffusion. In this work we fabricated 122 PIT wires with the regular Ag/Cu sheath and with the bi-layer barrier design, and compared them under various heat treatment conditions.
Epitaxial growth and studies on “emergent behaviors” of cuprate oxide thin film heterostructures are of the utmost importance for developing many superconductor electronic devices such as Josephson junctions, three-terminal devices, and circuit applications such as interconnects, ground planes, and multichip modules. In particular, the heterostructures made with high critical temperature (Tc) superconductor YBa2Cu3O7-x (YBCO) are interesting for device applications and basic science research, including studies of mechanisms for high-Tc superconductivity, 2D superconductivity, and measurement of the correlation energy. These heterostructures typically have the S/D/S, S/N/S, S/I/S geometries (S = superconductor, D = dielectric, N = normal metal, I = insulator), with the middle layer as the isolation layer, normal metal, or the insulator, where the intermediate layer materials must be structurally compatible and chemically stable at the processing temperature of superconducting thin films. Moreover, further complications arise concerning the surface superconductivity and the interfacial properties of the bottom and top thin film layers with the middle thin film layer. Although the mechanism of high Tc -superconductivity remains elusive, electron correlation plays an essential role in the superconductivity of high-Tc superconductors. The correlation energy, a measure of how much the presence of all other electrons influences the movement of one electron, can be directly obtained from a combination of Auger electron spectroscopy (AES) of cuprate oxide materials. It is a unique experimental tool since the Auger line-shape reflects a two-hole (or two-electron) density of states (DOS). This follows, for example, from discrepancies between various spectroscopic data and density of states curves computed by the local-density approximation (LDA).
Using the pulsed laser-based thin film deposition technique (PLD), we have fabricated “device-quality” (110)-oriented YBa2Cu3O7 (YBCO) and PrBa2(Cu0.8Ga0.2)3O7 (PBCGO) based S/I bi-layer and S/I/S
tri-layer heterostructures. Here, we present the theoretical studies using a full-potential spin-polarized relativistic Korringa-Kohn-Rostoker Green’s-function method (sprKKR) and experimental measurements, including X-ray reflectivity, pole figures, reciprocal space mapping, Auger electron spectroscopy, the density of states, and correlation energy on these cuprate oxide heterostructures.
Heavy ion or proton beams have the so called “Bragg peak” which enables a high dose administration to the tumor with greatly limiting the dose to the surrounding healthy tissues, besides of having a higher cell killing effect than photon beams. A safe and efficient treatment, high accuracy image guidance and good imaging techniques to distinguish a tumor from healthy tissues are required and crucial. MRI-guided proton therapy is the best option for this purpose. In order to minimize the effect of the magnetic field on the proton beam an open gradient MRI magnet is needed. This paper presents an electro-magnetic, mechanical and thermal FEM modeling of a 2 T actively shielded MgB2 open gradient MRI magnet for proton therapy applications. The magnet is cryocooler cooled with 10 ppm homogeneity in DSV (Diameter of Spherical Volume) of 0.5 m. A new class of MgB2 strand especially designed for MRI applications was considered for the winding the magnet. The magnet can get 2 T field and it can be operated up to 15 K.
Passive thermal control is essential for both terrestrial and space applications. In terrestrial applications, these coatings can reduce energy consumption for heating and cooling in buildings and automobiles. In space applications, they can drastically reduce the thermal load on the active cooling system. Thermal coatings with wavelength-dependent radiative characteristics, like reflectance and emittance, are desirable in both applications. In this study, we demonstrate the use of polymer nanofibers for passive temperature control for terrestrial and space applications. Specifically, we explore the use of polytetrafluoroethylene (PTFE) for terrestrial and space applications.
This study briefly describes the electrospinning fabrication process to create nanofibers and how specific process parameters can be varied to control the fiber geometry. To understand the role of material and fiber geometry, we measure the spectral reflectance, absorptance, and transmittance of various samples using spectrophotometers interfaced with integrating spheres. We also test if the samples show a change in radiative properties after exposure to ultraviolet light. We conducted calorimetric tests to determine the performance of various samples when exposed directly to sunlight.
We utilize multilayered structures with dynamically switchable optical properties for terrestrial applications to modulate their interaction with sunlight. Specifically, we test porous PTFE layers integrated with a spectrally selective (SS) absorber. This multilayered structure can provide tunable optical properties by wetting or dewetting the porous PTFE with a refractive index-matching liquid, allowing a highly reversible change in solar transmittance of 0.62. This variation allows the multilayered structure to switch between highly reflecting and absorbing states, which is tunable using different PTFE thicknesses. With this multilayered structure as the building exteriors, sunlight can be reflected or absorbed to reduce dependence on conventional heating and cooling systems driven by non-renewable energy sources. When exposed to 1 sun illumination under ideal conditions, this variation allows a 51℃ change in PTFE-SS steady temperatures. When applied to buildings as roofing materials, the PTFE-SS promises significant energy reduction with annual cooling and heating savings of around 77% and 27%, respectively.
For space applications, we combine polytetrafluoroethylene (PTFE) and polyethylene oxide (PEO) polymers to fabricate highly reflective coatings by electrospinning. By modifying the solution properties and coating thickness, we can control the solar reflectance of the coatings. Using different PTFE:PEO mixing ratios, nanofibers of different diameters, ranging from 1054±185 nm to 516±89 nm, were created on an aluminum substrate. As the coating thickness is increased from 0.3 to 1 mm, the average solar reflectance increases from 0.95 to 0.99. On the other hand, thermal emittance at room temperature was measured to be 0.7. Calorimetric testing of these samples was carried out under low vacuum conditions by exposing them to sunlight (1000 W/m2) inside a chamber maintained at 300 K. Relative to the incoming solar flux, only 1% of the energy was absorbed under these operating conditions. We anticipate the performance to be better in a cryogenic environment due to lower thermal radiation from the environment. With design optimization, further improvement or control over radiative properties is possible. Furthermore, these materials’ mechanical and radiative properties do not change significantly post-exposure to ultraviolet. Hence, these materials present a new paradigm for passive cooling in space and terrestrial applications.
Acknowledgments:
The authors acknowledge the support of the National Aeronautics and Space Administration under Grant No. 80NSSC21K0072 issued through the Space Technology Research Grants.
Suppressing condensation frosting using superhydrophobic surfaces can have a substantial impact on improving efficiency and safety in many industrial applications. However, the low surface energy coatings on such surfaces can be easily damaged during various harsh operations, which has limited the application potential of passive anti-frosting approaches. Here, we propose robust ceria-based anti-frosting surfaces, where superhydrophobicity is induced by not surface coating but adsorbed hydrocarbon. We also demonstrate how the incorporation of a hydrocarbon source as a binder to the ceria-based coating allows for the quick recovery of superhydrophobicity. In comparison to untreated aluminum surfaces, the developed coatings decreased the frost propagation speed and the ice adhesion strength by 60% and 89%, respectively. The coatings could maintain a low contact angle hysteresis even after 200 cycles of frosting/de-frosting robustness tests and 15,000 cycles of acidity/salinity exposure tests. Using a scalable one-step dipping process, the created coating was incorporated to a fin-tube type heat exchanger, and provided 210% enhanced heat transfer rate and 60% decreased pressure drop. The coatings also provided substantially improved robustness compared to the silane-treated superhydrophobic coating. These findings suggest that the developed ceria-based coatings can be helpful in creating scalable and resilient anti-frosting surfaces for real-world application operating at harsh environment.
This study investigated serration deformation (SD) behaviors of direct-energy-deposited (DED) and wrought CoCrNi medium entropy alloy as well as DED stainless steel 316L (SS316L) at ultra-cryogenic temperature of 15K. In-situ neutron diffraction was employed to examine tensile mechanical properties, localized microstructures and SD behaviors at 15K. Enhanced peierls stresses and severe dislocations pile-up at 15K resulted in an exceptional strength-ductility combination for both alloys. Higher initial dislocation density of DED alloys induced superior yield strength and delayed the onset of SD, as compared to wrought alloy. A stress drop occurring to the SD exhibited a significant increment after ultimate tensile strength (UTS), which finally led to an unexpected fracture. DED SS316L exhibited higher stress drop at the same stress level of strains than CoCrNi alloys, which is associated with martensitic transformation. The different {hkl} orientations exhibited a different behavior in terms of a magnitude in stress drop as well as subsequent linear stress-strain response after the SD. The current study reveals that the SD behavior is highly influenced by dislocation structure and microstructure features.
Nowadays, low-dimension materials have been widely used in microelectronics, biomedical engineering and aerospace technology, so it is necessary to develop small-scale devices to understand and predict the mechanical performance at cryogenic. In this study, a mechanical properties measurement for low-dimensional samples at cryogenic were designed and established. Three kinds of low-dimensional samples, such as stainless steel and SIC fibers, with different diameter were tested in this device at 77 K, 90 K and 300 K. The stress-strain behaviors of these low-dimensional samples are well described and compared to the standard size samples, which illustrated the specimen size effect and the cryogenic properties. Subsequently, this work provided more mechanical properties of low-dimension samples and insights into the size effect exploration at cryogenic.
NASA frequently needs thermal contraction data for materials to be used in cryogenic space flight missions. To satisfy this need, we developed an apparatus and a high-precision technique for performing such measurements using a commercial fiber-optic-based position sensor. We describe the measurement process and its verification using a copper sample. We also present data for two materials which we characterized for potential NASA use.
The Deep Underground Neutrino Experiment (DUNE) utilizes neutrino sensors that are submerged within liquid argon to measure the electron trails left by neutrinos. The sensors require specially designed supports to ensure they remain precisely positioned even after the thermal contraction of the sensors and the cryostat that occurs during cooldown. These supports must ensure that the fragile cryostat floor is protected yet also allow the sensor planes to slip in order to avoid any damage. Further, the supports must ensure that the center of contraction is a predetermined location. These objectives are satisfied by utilizing an intermediate slip plane in the support itself that provides a lower coefficient of friction compared to the interface between the support and the cryostat floor. The design of these supports required knowledge of the coefficient of friction for a variety of materials at cryogenics. It was found that the friction associated with materials such as metals, ceramics, and polymers have all been studied very little in cryogenic environments; there is specifically not much data available relative to the static coefficient of friction associated with polymers polymers at low temperature. Therefore, a test apparatus was built to measure the static coefficient of friction of different materials. The apparatus uses a linear screw to apply a force to a test sled contained in a low temperature, moisture controlled environment. Using this test apparatus, a number of tests with different materials were carried out. Some of these results are discussed in this paper.
In recent years, people in the world have greatly changed purchase and consumption habits due to the booming electronic commerce services and the effects of COVID-19 pandemic. In terms of daily diet, more and more people use online food ordering and delivery services (such as Uber Eats, DoorDash, Deliveroo, Foodpanda, etc.) and the amount of food packaging wastes has thus increased substantially. Multilayer packaging materials (MPMs), which are normally composed of paper, polymers, and/or aluminum, are widely used as food containers for delivery and storage; however the recycling rate of waste MPMs is very low. Without separating the component substances, the waste MPMs can not be introduced into the current recycling systems of paper, polymers, or aluminum, thus significantly increasing the difficulty and costs of the MPMs recycling. In this study, the cryogenic milling was used to assist the recycling of MPMs due to the difference in the property under an ultra low temperature between the component substances. Most polymers lose the ductile properties below their glass transition temperature, and it is therefore easier to reduce the size of polymers and to separate polymers from aluminum. The waste beverage containers manufactured by Tetra Pak were collected and used as experimental materials. This type of MPMs contains four layers of polyethylene, one layer of paper, one layer of aluminum foil, and inks. A vibratory micro mill (Fritsch, Pulverisette 0) with a special accessory (Cryo-box) was employed to conduct the cryogenic milling. The amplitude was set between 1 and 3 mm, and the grinding time was controlled from 5 to 15 min. The effects of the addition rate of liquid nitrogen were also examined in this study. After the cryogenic milling, the ground MPMs were separated into different particle size ranges and then digested with acids by using a microwave-assisted digestion procedure. The digests were analyzed with the inductively coupled plasma-optical emission spectrometry (ICP-OES, Thermo Scientific, iCAP PRO) to determine the concentration of aluminum. The results showed that a sufficient pre-cooling process with liquid nitrogen for MPMs was helpful to the following cryogenic milling. A pretreatment process of immersing the MPMs into water or water-ethanol mixtures also increased the efficiency of cryogenic milling. After the cryogenic milling, aluminum tended to remain in large particle size ranges, while most of paper and polyethylene were ground into small particles. However, aluminum was also ground into small particles with high grinding intensity (high amplitude, long grinding time, or both), and this may not be useful to the separation of the substances. Generally, the cryogenic milling can effectively reduce the particle size of MPMs and change the distributions of the component substances, thus making MPMs easier to be recycled. Some physical methods (flotation, electrostatic separation, etc.) or chemical extraction methods (acids, organic solutions, etc.) could be used to recover high-quality materials further.
A 4K hybrid JT cooler is developed as an alternative to precool the adiabatic demagnetization refrigerator (ADR) of Hot Universe Baryon Surveyor (HUBS) mission which is proposed to study “missing” baryons in the universe. The 4K hybrid JT cooler is composed a 4He JT cooler precooled by a two-stage thermally coupled pulse tube cooler. Recently, the two-stage pulse tube cooler is optimized to provide more precooling power for the JT loop. And both the counter-flow heat exchangers and the evaporator are redesigned to enhance their heat transfer process. Then, improvement measures are conducted on the compression system of the JT loop. Eventually, the performance of the hybrid JT cooler is able to provide sufficient precooling power for the ADR of HUBS. Besides, discussion of the supporting structure of the cold end of the JT cooler is presented in this paper.
NASA is considering a “probe” class mission with a far-infrared imaging and spectroscopy space telescope. A critical technology for this mission is an efficient, high capacity, low-temperature cryocooler with low exported vibrations to enable its cryogenic instruments to achieve exquisite sensitivity and low internal noise to observe far distant faint cosmic sources. This paper compares the performances of a JT cooler with 4He and 3He working fluids, in terms of cooling capacity, input power, and optimal operating pressures. The paper will also discuss the effects of switching working fluids on the thermal performance of recuperators and the JT throttle design. Next, the paper will discuss the sensitivities of the cooler performance to the heat sink temperatures and cooling temperatures. Flow performance test results with a flight compressor development unit using these two fluids will be presented, as well as predicted cooler performance based on the measured compressor performance data.
Miniature Joule-Thomson (JT) cryocoolers are attractive for many applications due to their small size and resulting fast cool-down time. Finned-tube heat exchangers are the most widely used heat exchanger for miniature JT cryocoolers. The basic configuration, known as a Giauque-Hampson (GH) or coiled tube heat exchanger, involves the high-pressure stream flowing through a finned-tube that is helically coiled upon a cylindrical core while the low-pressure return stream flows over the fins in the annular space created by the core and the inner diameter of a shell. While it has been suggested that the heat transfer coefficient (htc) of the return stream is a key parameter affecting the behavior of the entire GH heat exchanger for a mixed-gas Joule-Thomson (MGJT) cryocooler, there is still no data or theory in open literature that characterizes the heat transfer and pressure drop characteristics of two-phase multi-component mixtures on the shell side in these heat exchangers.
The experimental work in this study aimed to gain insight into these thermal characteristics by developing a test facility capable of measuring the two-phase htc for this geometry at operating conditions of interest to MGJT cryocooling. The capabilities of the test facility were demonstrated. The size of the GH heat exchanger prototype and operating parameters of the test facility were consistent with those of interest for MGJT cryocoolers. Measurements of the two-phase htc of the mixed gas on the shell-side of the GH heat exchanger prototype were collected. For the mixture examined, the two-phase htc was found to be between 12 to 19 W/m2-K with uncertainties of approximately 12% for qualities in the range of 0.31 to 0.62. This data reveals that the shell side is the dominant thermal resistance for these operating conditions, even though the fins provide a larger surface area. Therefore, the htc of the mixed gas on the shell-side is crucial for cryocooler design and predicting the overall performance. The data collected clearly demonstrates the need for and importance of developing accurate correlations for two-phase multi-component mixtures on the shell-side of GH heat exchangers for operating conditions consistent with MGJT cryocoolers. Only with these correlations can the effects of the mixture selection on the pressure drop and the effectiveness of the heat exchanger be considered in the design of a MGJT cryocooler for optimal performance.
Open cycle Joule-Thomson (J-T) cryocoolers that operate with pure nitrogen and provide about 1 W of refrigeration effect at 80 K are used extensively in missiles. There is a worldwide interest in developing single-stage miniature J-T cryocoolers that operate with mixtures of refrigerants for cooling detector elements in space applications. Detector cooling enables noise reduction and thereby improves the signal-to-noise ratio. Heat exchangers of high effectiveness (typically greater than 97%) are required for these cryocoolers to function. The attainment of such high effectiveness in miniature heat exchangers makes designing these systems very challenging.
A miniature palm-sized variable speed compressor with a stroke volume of 1.4 cc is used to drive the cryocooler, and a mini-channel (∅<3 mm) multiple tubes in tube heat exchanger with a mean coil diameter of 90 mm and 160 mm long is used as an internal heat exchanger. A lowest temperature of 92 K is achieved with the cryocooler with 1 W of refrigeration effect at 99 K, and a maximum cooling capacity of 3 W is achieved at 104 K. The performance characteristics associated with the cryocooler, namely, the cooling capacity, exergy efficiency, effectiveness of the heat exchanger, and heat load characteristics, with three different nitrogen-neon-hydrocarbon refrigerant mixtures for achieving a few watts (1-3 W) of refrigeration effect in the temperature range of 90 – 100 K will be presented.
Keywords: Miniature Joule Thomson refrigerator, Multiple tubes in tube heat exchanger, Refrigerant mixtures.
The cell of the sorption compressor developed in this paper has a thin-plate shape to accelerate the pressure swing by reducing the heating and cooling periods. Its width, height and thickness are 100 mm, 100 mm and 4.6 mm, respectively. Two identical cells filled with 22.8 g of charcoal mass are operated alternately to generate and maintain significant pressure difference for the 5 K J-T cooler with the pre-cooling temperature of 15 K. The designed nominal pressure of the high-pressure and the low-pressure parts of the J-T cooler are 1000 kPa and 196 kPa, respectively. The mass flow rate and the pressure gradient of the thin-plate sorption compressor with commercial check valves are measured experimentally. As the performance of the compressor, COP of the compressor is estimated and compared with the compressor of previous researches. Furthermore, to reduce leakage rate and thermal inertia of check valves in the compressor, miniaturized check valve is specially designed and fabricated to replace the commercial valve. When the flow direction is reversed in the valve, the leakage is passively prevented by contacting two metal surfaces at low temperature (30 K). The essential parts of the valve are critically miniaturized to reduce the overall thermal inertia of the compressor system. The cracking pressure and the leakage rate of the developed check valve and the commercial check valve are measured to compare.
This paper presents initial experimental results of a Modified Collins cycle cryocooler designed for space cooling applications. It describes a high efficiency and lightweight single stage cryocooler design that will provide about 100 W of cooling at temperatures on the order of 90 K. With multi-staging, cooling to 4 K should be possible with this architecture. A single stage machine with a floating piston is experimentally demonstrated with helium as the working fluid. Cryocooler construction materials and control system methodologies will be discussed.
SLAC National Accelerator Laboratory has upgraded to LCLS-II, featuring a 4 GeV superconducting accelerator composed of 37 cryomodules and two large helium refrigeration systems with a cooling capacity of 4 kW at 2.0 K. The cryogenic system at SLAC is the successful outcome of a seven-year partnership between SLAC, FERMI Lab, and Jefferson Lab. This paper highlights the joint efforts between Jefferson Lab and SLAC in the development and implementation of the LCLS-II Cryogenic Plants. While Jefferson Lab led the design and procurement of critical components, SLAC was responsible for the infrastructure, integration, installation, controls, and commissioning. The paper documents the project organization, key milestones achieved, and key lessons learned throughout the process.
End station refrigerator 2 cryoplant is needed to provide cryogens to three of the four experimental halls to support 12 GeV experimental demand and in particular to the near-future MOLLER experiment at Jefferson Lab. End station refrigerator 2 cryoplant consists of 4.0 kW at 4.5 Kelvin cold box and two-stage compressor systems, which are received from the Superconducting Super Collider (SSC) project and refurbished to meet the operating needs. End station refrigerator 2 cryoplant also consists of new 50+ m long cold transfer line, bayonet CAN, utility system and control system. The paper will describe the fabrication progress, challenges faced and mitigation adopted for the cryoplant including future workplan.
In 2019, Linde received the order to deliver a large 4.5K helium refrigeration system for the Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The particle accelerator for heavy ions (SIS100), a fragment separator (Super-FRS) and several experiments are operated using superconducting magnets, all cooled with helium supplied from one central cryoplant.
Due to the different requirements of the individual systems, a wide range of cryogenic loads are covered by the cryoplant. While operating in a steady state, the main cold box delivers up to 14kW at 4.5K and 49kW at 50 to 80K.
The Super-FRS has a large cold mass of ~1500t. Cool-down and warm-up are rare and time-consuming procedures. Therefore, a separate unit with indirect LN2 cooling is provided. Advantageously, the compressor of this cool-down and warm-up unit can be used as a redundant compressor for those of the main cold box. It may replace the function of one of the two HP or two LP compressors.
The combination of floating high and medium pressure with a process integrated 20,000L LHe dewar enables rapid adaption to load change. Using a floating pressure cycle, high efficiency is maintained even at low turn-down operations; as low as only 20% of the design load.
The paper covers the process design and the control strategies for load adaption.
MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) will be the world's first research reactor powered by a particle accelerator. MYRRHA will be composed of a 600 MeV LINAC accelerator with a large number of cryomodules and a 100 MW thermal power subcritical nuclear reactor cooled by lead-bismuth.
The MINERVA project is the first phase of the MYRRHA project. It consists of a 100 MeV, 4 mA continuous-wave proton linear accelerator (LINAC) among other facilities. The MINERVA LINAC takes advantage of superconducting radiofrequencytechnology in order to provide acceleration from approximately 17 MeV to 100 MeV, using bulk niobium (Nb) single-spoke cavities cooled at 2 K by saturated superfluid helium (He II). Sixty accelerating superconducting cavities will be installed in 30 cryomodules (having two cavities each), for a superconducting section length of approximately 100 m. The MINERVA cryoplant will supply the required cryogenic cooling power of the LINAC through cryogenic lines and cryogenic valve boxes. MINERVA has also important requirements concerning operating modes: limitation of thermal cycles and high accelerator availability, which require a very high operation reliability for the cryogenic system.
The current paper presents the preliminary design of the MINERVA cryoplant and the strategy to comply with high reliability. It describes the LINAC cryogenic system architecture, the different operating modes, the heat loads, the cryoplant main requirements and the strategy to comply with high reliability in terms of redundancy and selection of components. The MINERVA cryoplant shall supply helium flows at 40 K for the thermal shielding, at 5 K for the cooling of the radiofrequency couplers and at the 2 K for the superconducting cavities in the cryomodules. The total equivalent power of the MINERVA cryoplant is about 3 kW at 4.5 K. The cryoplant is composed of a warm compression station including sub-atmospheric volumetric compressors and high-pressure helium gas storages both at room temperature, a refrigeration cold box with cold centrifugal compressors for the 2 K operation of the superconducting cavities.
Funding source: This work is supported by the MYRRHA programme at SCK CEN (Belgium).
With the development and application of cryogenic science, cold energy storage (CES) has widespread applications in industry. Solid-phase packed bed is a promising medium for CES due to its simple structure, low cost, and low risk of flammability and explosion. However, most of the previous studies have primarily focused on the sensible heat storage characteristics of single-phase flow inside the packed bed. In this paper, a latent heat storage solid-phase packed bed for CES is proposed. The basic principle is that the cryogenic liquid nitrogen enters the packed bed directly to store cold energy in the CES process, and the pressurized nitrogen obtains cold energy and is liquefied in the cold energy release process. The temperature distribution of the gas-liquid two-phase flow through the packed bed is investigated experimentally, and its thermocline and inlet/outlet temperature are analyzed. The results demonstrate that the temperature distribution of the packed bed is different from previous studies due to the phase change, especially in the cold energy release process, where there is a change from the pure liquid phase to the gas-liquid two-phase to the pure gas phase at the outlet. The conclusions obtained from the study can provide valuable insights into the design of latent heat storage packed beds for CES.
Mixed-refrigerant Joule-Thomson refrigeration (MJTR) is the primary cooling method for the temperature range from 80 to 230 K. It can be used in cryosurgery, high temperature superconductivity and sensor cooling. However, most of the studies are on nitrogen-hydrocarbon refrigerants, which are not allowed in applications where there is a special need for flammability. Therefore, non-flammable mixed refrigerants were investigated in this study.
The composition of the mixed refrigerant is a key factor in the system performance (refrigeration temperature, refrigeration capacity, etc). However, the purely mathematical optimization method lacks physical knowledge in optimization process, and may have disadvantages of time-consuming. In this study, the isothermal throttling effect of mixed refrigerants is optimized, and the optimization process is based on the partial molar enthalpy difference of each component. The method is based on thermodynamic properties and is time-saving.
Non-flammable mixed refrigerants with refrigeration temperatures from 100 K to 140 K were designed in this study. The results show that the designed mixed refrigerant has a higher COP compared to the reference. Argon has an advantage at refrigeration temperatures from 120 K to 140 K, while nitrogen has an advantage from 100 K to 120 K. In addition, systems with pre-cooling stage were studied and the results showed that the highest exergy efficiency is achieved at a pre-cooling temperature of 250 K. The exergy efficiencies with pre-cooling stage are nearly twice as high as that without pre-cooling. Therefore, a pre-cooling stage for nonflammable mixed refrigerants is necessary where there is no requirement for system size.
Acknowledgement: This work is financially supported by the Key Project of National Natural Science Foundation of China under the contract number of 52036010 and Youth Innovation Promotion Association CAS (2021028).
In a Linde-Hampson cycle, the working fluid usually produces a throttling effect in the expansion element. However, when a mini-channel heat exchanger is applied to the cycle, the high-pressure flow can also generate a throttling effect in the narrow channels, known as the distributed J-T effect. The distributed J-T effect (or distributed pressure drop) is usually considered to have a negative impact on the cycle performance. However, it may be acceptable under special conditions. In this paper, the effect of the distributed J-T effect on the performance of mixed refrigerant Joule-Thomson (MRJT) refrigeration cycles is investigated. The exergy loss distribution of the cycle is investigated under different conditions: a fixed compressor inlet temperature, a fixed heat exchanger UA value, and a fixed minimum temperature difference of the heat exchanger. The effect of the distributed J-T effect on the cycle performance is also examined. It can be seen that the distributed J-T effect can be used to maintain high cycle performance under specific conditions, and the distributed J-T effect in a specific temperature region only affects the exergy loss in the lower temperature region than it. In addition, the maximum allowable pressure drop of the MRJT cycle is consistent with the isothermal throttling effect of the mixed refrigerant when the minimum heat exchanger temperature difference is defined. At the same time, only the exergy loss distribution between the heat exchanger and the throttle valve will be influenced by the distributed J-T effect at a constant compressor inlet temperature. The conclusions of this paper provide a reliable reference for exploiting the distributed J-T effect, especially for the design of compact miniature J-T coolers.
Clean-energy propulsion machines, including trucks, tractors, ships, and aircraft, for heavy-duty and long-range mobility have moved, by necessity, to onboard liquid hydrogen (LH2). However, the established method of storage and transfer is problematic due to losses and for any duty-cycle of a sporadic or on/off nature. Integral servicing system methodology is needed for both safety and cost effectiveness in the key drivers of time savings, product savings, and venting exposures. Modern controlled storage technology enables quick and effective vehicle servicing at the point of use. Simulations of controlled storage/transfer (CS/T) methodologies are performed using a multi-purpose LH2 simulation test platform comprised of two primary systems: Cryostat CS900 tank and transfer system and the LS20 liquefaction/refrigeration and storage system. Testing includes both steady-state and transient modes of operation to demonstrate both zero boiloff (ZBO) and zero-loss transfer (ZLT) modes. Technical areas of use include product development for tanks, refrigeration, transfer systems (lines, dispensers, pumps, valves); experimental validation of analytical models and thermofluidic properties; thermal insulation performance test data under relevant conditions; thermophysical characterization of materials and structures; and instrumentation and sensors development, and tank boiloff and heat flux engineering design data. Descriptions and preliminary test results are given along with thermal performance analyses from real-world testing and experimentation.
Liquid hydrogen cold-chain logistics vehicle (LHCCLV) is a special vehicle using liquid hydrogen (LH2) as the source of both power and cold energy. For the high energy consumption in the hydrogen liquefaction process has been regarded as a major weakness of LH2, the utilization of cold energy in LHCCLV can improve the economic performance and competitiveness of LH2. Because of the high energy storage density of LH2 and the relatively high efficiency of fuel cells, we find the cold energy can not meet the demand of LHCCLV. Therefore, we consider enlarging the cold energy by promoting the para-ortho hydrogen conversion (POC), whose reverse reaction consumes even exceeds 20% energy in the hydrogen liquefaction process. POC can not be carried out quickly without a catalyst, so we can control the ‘valve' of the POC cold energy by reasonable process design, which is different from latent heat and sensible heat. In this paper, numerical models of releasing hydrogen from the LH2 and supercritical hydrogen tank are established in MATLAB, and the influence of POC on the supply of cold energy is analyzed. The changes in instantaneous and total cold energy supply under different working conditions are analyzed, and the important influence of POC is confirmed. At the same time, the influence of POC on the operation status of the storage tank is analyzed. The beneficial effect of POC is quantified in the paper, especially for the cold energy supply. This paper provides an important reference for the research and development of LHCCLV and also provides guidance for the comprehensive utilization of cold energy in other situations, so as to promote the improvement of the economy of hydrogen energy utilization routes in the form of LH2.
In this paper we give a progress update on the cryogenic design for cooling a 20 MW class, partially superconducting generator with stationary field coils for offshore wind renewables industry. This is a continuation of an earlier program on a 10 MW system dating back ten years. Whereas this new power rating increase leads to a radial diameter expansion of the superconducting field coils from 4 to > 8.5 m, it maintains the axial length.
We show the design based on this scaled up with enlarged diameter. The field coil size increase asks for higher cooling power that leads to a bigger cold box size to accommodate the cryocoolers. In the design, as many as 8 cryocoolers can be accessed and serviced from the nacelle that houses the main cryogenic components. A typical thermal load balance sheet with all components is given and compared against the available cryocooler cooling power at different operating conditions.
Due to the cryocoolers’ local point of contact cooling within the nacelle, the temperature gradient of the thermal shield that fully encloses the cold mass with its embedded field coils needs to be balanced out to minimize the heat burden on the field coils. This requires additional analytical efforts and implementation of further design features.
The extended nacelle houses the cold box with its cryogenic infrastructure. The interface for the envisaged cryogenic pushbutton closed-loop circulating system remains invisible, requires no handling of cryogenic liquids and is hermetically closed.
The field coil diameter increase also leads to a greater initial helium gas storage volume. In addition, it requires higher initial room temperature fill pressure within the toroidal helium vapor storage tanks and in cooling tubes connecting to the cryocoolers. The toroidal helium gas tanks are thermally coupled with the thermal shield so that helium convection inside the storage tank can improve heat transfer and reduce the temperature gradient of the thermal shield.
Besides those heat transfer challenges, additional mechanical strain within this large structure is exerted on the torque tubes during initial cooldown and when energizing field coils.
Some of those design challenges are quite unexpected, leading to novel workarounds in order to maintain the chosen cooling strategy. Finally, we assess those design limitations in view of further cryogenic scalability with emphasis on manufacturability and assembly.
This material is based on work supported by the United States Department of Energy under award number DE-EE0008787 through the Wind Energy Technology Office of the Office of Energy Efficiency and Renewable Energy.
The high-temperature superconducting magnetic energy storage system (HTS-SMES) utilizes the superconducting coil (SC) to store the electric energy in the magnetic field, which has the advantages of high efficiency, fast response, infinite charge-discharge cycles, etc. Coupling SC (CSC) with two or more SCs made of different HTS materials can improve the utilization rate of HTS tapes, reduce the manufacturing cost, increase the energy storage density of the magnet, and decrease the leakage field. Although the CSC has advantages over conventional SC, the coupling magnetic field makes precise power and current regulation of the individual SC difficult. Moreover, the self-inductances of the individual SCs with different materials are usually different. The induced voltage due to current fluctuation is therefore different, which makes it necessary to design power converters with different power ratings connected to each SC. To solve the difficulties in the application of SMES with CSC, a novel modular power conditioning system (MPCS) and decoupling control for SMES are proposed. With the MPCS, the power rating of individual SC can be flexibly designed by selecting the number of power modules. The power and current of individual SC can be precisely controlled with the decoupling control. Simulation results verified the efficacy of the proposed approaches.
Pulsed power loads such as high-field pulsed magnets and lasers require efficient sources of energy. Superconducting Magnetic Energy Storage (SMES) has been investigated as a source of stored energy for a variety of applications. High Temperature Superconductors (HTS) allow SMES systems to operate at temperature higher than 20 K, making the required cryogenic systems simpler compared to the liquid helium cooled systems. Emerging HTS applications such as compact fusion are leading the development of high ampacity HTS cables. The high-ampacity HTS cable designs are also suitable for SMES applications. In pursuit of finding an efficient energy source that can supply the required multi-kA current and application specific milli-second pulse shapes, we are exploring SMES. The paper will discuss the SMES designs and the electrical simulations to assess the design parameters of a SMES. The challenges of the power conditioning systems for charging SMES and transferring the energy from SMES to the pulsed loads are also discussed.
Hydrogen-Electric aircraft technologies require electric propulsors to achieve the goal for zero emission. Those electric propulsors are preferably superconducting with high current density, resulting in an increased power density. Propulsors can either be partially or fully superconducting. In this paper we show a cryogenic cooling concept feasible for indirect cold mass cooling in the above 20 K or higher temperature range, depending on conductor choice.
For a number of reasons, we would not bath-cool the propulsor (direct cooling) but prefer an indirect cooling approach where field and armature windings are not directly exposed to hydrogen.
The stator of this motor is exposed to the rotating magnetic field of the field coils that rotate at e.g., 4500 rpm for the CHEETA design initiating eddy currents in the armature structure. Those AC losses need to be transferred to a cooling medium. In the proposed configuration a helical cooling coil is mounted on the inner surface of the stator. The cooling coil is configured such that liquid hydrogen can pass through the stator. We call that an armature winding cooled by highly efficient liquid hydrogen forced-flow boiling. The heat load generated from the armature due to those AC losses is quite substantial and may be around 2.3 kW.
As an example, we discuss heat transfer options across both, static and rotating surfaces for indirectly cooling of a fully superconducting motor for all-electric aircraft, where stator and rotor are exposed to a vacuum environment.
We selected and analyzed a novel rotating thermal intercept between a stationary armature and a rotating field coil not based on thermal slip rings, rotating cryocoolers, rotating thermosiphons or cryogenic immersion techniques, that is efficient and can be implemented and adapted as well for different thermal loads.
Authors gratefully acknowledge support for the Center for High-Efficiency Electrical Technologies for Aircraft (CHEETA) by NASA under Award 80NSSC19M0125.
Various space-technology-related applications significantly benefit from the extended availability and capabilities of High-Temperature Superconductor (HTS) systems. This aspect accompanied by initial networking as well as research and development projects such as the Magnetohydrodynamic Enhanced Entry System for Space Transportation (MEESST) activity leads to the qualification of critical subsystems such as HTS coils under simulated harsh environmental conditions encountered during atmospheric entry and by electric propulsion systems in operation.
The international consortium of the European Union project MEESST is currently preparing a plasma probe equipped with a HTS coil for the deflection of ionized entry flows to investigate heat flux mitigation and communication blackout mitigation. The consortium consists of the Katholieke Universiteit Leuven (KU) and the von Karman Institute for Fluid Dynamics (VKI) in Belgium, the University of Luxembourg (UL) in Luxembourg, the University of Southampton (US) in the United Kingdom, the Institute of Space Systems (IRS), Karlsruhe Institute of Technology (KIT), Theva Dünnschichttechnik GmbH, and Neutron Star System UG (NSS) in Germany, Absolut System (AS) in France, and Advanced Engineering Design Solutions Ltd. (AEDS) in Switzerland. Over a duration of 42 months, the project encompasses the experimental design and implementation, as well as an extension of computational modelling capabilities for characterizing plasma flows in presence of applied magnetic fields and accounting for radiation. The consortium’s expertise, close collaboration between team members, and the mutual verification level of the experimental and computational tools deployed build a unique constellation with the potential to significantly expand the understanding of weakly ionized plasmas exposed to applied magnetic fields in various space technology applications.
The contribution will summarize the activities so far and in addition, it will highlight potential applications such as those mentioned for MEESST. Furthermore, it will cover other potential applications such as applied-field MPD thrusters, advanced MHD-based electric space propulsion, and radiation mitigation.
We report on bulk superconductor space experiments with the Earth’s magnetic field which has been recognized as a major task for a better understanding of our planet. In the co-operational Magvector/MFX project on the International Space Station (ISS) in 2014-2018 we studied the interaction of the fast moving Earth magnetic field with materials of variable and perfect conductivity. For this, a 10 cm YBCO superconductor was prepared, installed, and cooled in vacuum cryostat onboard the ISS. MFX consisted of a lightweight vacuum cryostat, operated at 10E-5 mbar with a 4 W modified Stirling cryo-cooler up to 45 K. An external 3D-Helmholtz coil nullifies the surrounding unwanted electromagnetic fields. High-sensitive flux gate sensors monitored the magnetic configuration when the HTS plate was cooled down to cryogenic temperatures. Screening and field concentration effects of the Earth’s magnetic field were observed and will be discussed. In parallel, the magnetic performance of two single crystal 30 mm YBCO bulks was scanned before and after the German “blue dot” ISS mission to observe any changes. Mechanical and thermally induced low-cost magnetic flux compression for future far-distance space missions has been successfully tested. A one-step trapped flux enhancement of up to 30% was obtained which allows future spacecraft shielding and braking functions.
Space telescopes are required for many astrophysics observations, either to reduce atmospheric perturbation (in the infrared spectrum) or simply to make these detections possible (in the X-Ray spectrum for example). Several missions are in development, such as Athena. Athena is a mission of the European Space Agency (ESA), with additional international contributions, dedicated to X-Ray observation. One of its instruments, X-IFU, will use Transition Edge Sensors (TES) detects and precisely measure the energy of X-Ray photons. These sensors require a temperature of 50 mK to reach their ambitious sensitivity goals.
In space, this temperature can be reached using Adiabatic Demagnetization Refrigeration (ADR). A cooling system based on this technology is currently being developed for the X-IFU instrument. ADR is based on variation in magnetic field to achieve lower temperatures and produce a cooling effect. The magnetic field of the order of 1 T in a volume of 10s of cm3 is produced by a superconducting coil with high winding number and current limited to approximately 2 amps. Even though this current is low compared to most earth-based systems, metallic current leads to link the high- and low-temperature stages would cause high thermal loads, unacceptable for the limited capacity of the space cryogenic cooling chain. Therefore, a harness consisting of superconducting current leads is planned to reduce the thermal loads at the low-temperature stage.
As part of an ESA contract, our team designed, built and tested such a space compatible harness. This harness includes the electrical interfaces at both ends as well as mechanical support. Its development is geared toward the Athena/X-IFU needs and it is capable of operating between interfaces at 80 K and 4 K. The harness is based on industrially available Rare-Earth-Barium-Copper-Oxide (REBCO) High Temperature Superconductor (HTS) tapes. The tapes were laser-cut by our group to fulfill our specifications, Parylene coated and reinforced with Kapton laminate tape for mechanical and insulating purposes. After characterization of the single tapes, the assembled harness has been subjected to an extensive qualification sequence including thermal cycling and mechanical testing based on launch loads requirements. This paper will summarize the technical design choices for this space compatible HTS harness. It will discuss the test results and propose some perspectives for the next iteration of HTS current lead development.
High reliability is an essential requirement for all spaceflight hardware. XRISM, a follow-on mission to the Hitomi x-ray observatory, also uses 2G REBCO tapes as current leads for the superconducting magnets that are a key component of the Adiabatic Demagnetization Refrigerator (ADR) that cools the detector array. While the Hitomi Soft X-ray Spectrometer (SXS) worked flawlessly in orbit, during its development there were indications that the critical current of its specialized REBCO tapes could degrade over time when exposed to normal-humidity air. To demonstrate that the updates to the XRISM HTS lead assemblies had mitigated this risk, a series of tests were carried out to measure the stability of Ic of dozens of samples over a period greater than the flight assemblies were exposed to air during integration and test. The test rig allowed not only the measurement of the sample Ic, but also the localization of the voltage rise as the current approached Ic. We will discuss the trends in the critical current of the samples, as well as localization of lower Ic regions.
Entering the atmosphere of a planet at high velocity poses major challenges for spacecraft. High heat fluxes caused by the compressed and partially ionized gas at the front of the spacecraft can heat the surface to temperatures, which can exceed the operational temperatures of the structure materials significantly. A thermal protection system (TPS), e.g. with ablative heat shields as in the Mercury, Apollo and Gemini missions or with radiatively-cooled heat shields as used on the Space Shuttle, is necessary to protect the spacecraft from high heat fluxes, but these systems are often heavy and fragile. Another problem that is well known since the early days of space flight is the radio-blackout phenomenon. The ionized gas in the plasma can block radio waves and lead to a loss of GPS data telemetry or communication with ground stations.
In the framework of the European project MEESST (MagnetoHydroDynamic Enhanced Entry System for Space Transportation) we have developed a high temperature superconducting (HTS) magnet for ground experiments in plasma wind tunnels to demonstrate that both heat flux mitigation and radio blackout mitigation can be achieved by magnetohydrodynamic (MHD) effects. The magnet and its cryogenic system have been designed to fit in a probe that will be installed in plasma wind tunnels at the Institute of Space Systems (IRS) of the University of Stuttgart, Germany, for heat flux mitigation experiments, and at the von Karman Institute (VKI) for Fluid Dynamics in Brussels, Belgium, for radio blackout mitigation experiments. A cryocooler and a closed gaseous helium loop will be used to cool the HTS magnet to a temperature of approximately 30 K. The HTS magnet was designed to produce a magnetic field in the range of 1-2 Tesla at the front surface of the probe, which has a warm bore to accommodate measurement equipment. The non-insulated magnet with inner and outer winding diameters of 66 mm and 143 mm, respectively, consists of 5 single pancakes wound with a total length of 700 m REBCO (Rare Earth-Barium-Copper-Oxide) coated conductor tape.
In this paper we will give a short introduction to the scientific background and the consortium of the MEESST project. We will present the boundary conditions for the design of the magnet, calculations of field distributions and show how the pancake coils were wound with a robotic winding system.
A preliminary test of the conduction-cooled magnet was carried out at the Karlsruhe Institute of Technology (KIT). Results will be presented and an outlook to further work in the project and necessary steps for future flight applications of plasma shielding magnets will be given.
In this paper we will report the recent progress of making ternary APC (Artificial Pinning Center) Nb3Sn conductor using internal oxidation technique in Hyper Tech. Our ternary APC Nb3Sn conductors with Ta and either Zr or Hf doping demonstrated substantial grain refinement and significantly increased Jc,nonCu, while retaining the high Bc2 values of the best ternary Nb3Sn conductors. The non-Cu Jcs of these ternary APC conductors have surpassed the best state-of-the-art Nb3Sn and the Jc,non-Cu specification of the Future Circular Collider (FCC). Their Bc2 was about 28 T, about 1-2 T higher than present state-of-the-art conductors. This APC strand has been made to 217-filament restack strands getting filament size of 35 micros at the 0.7 mm strand. These newly developed APC wires have RRR above 150 while surpassing the Jc,non-Cu specification of the FCC.
We will also report the progress in increasing the specific heat (Cp) of the Nb3Sn conductors to increase the energy margin against quenching by adding certain high Cp material in the strands. We successfully made 217-filament restack strands with filament size of 35 micros at the 0.7 mm strand and demonstrated the higher specific heat strands has much higher Minimum Quench Energy (MQE) values while keeping its high Jc and high RRR.
The goal of building economic 16 T accelerator magnets requires Nb3Sn conductors with Jc much higher than state of the art. Thus, a lot of efforts in the Nb3Sn community have been focused on improving Jc (while keeping RRR and effective subelement size deff in the acceptable range). However, a very important factor that is also critical for this application but has been overlooked is the persistent-current magnetization M, because large M leads to critical issues such as flux jumps, field errors, and large a.c. loss. Conceptual design studies for the proposed Future Circular Collider (FCC) 16 T dipoles show that the large M is a significant problem to address. One way to reduce M is to reduce deff, but this may sacrifice Jc as deff is below 30-40 micron. In this study we measured the M-H loops of RRP® and the new APC conductors up to 25 T. The results showed that the APC conductors have higher non-Cu Jc at high fields (e.g., 32-41% higher at 16 T) and simultaneously lower non-Cu Jc at low fields (e.g., 28-34% lower at 1 T) compared with the RRP®. Assuming that both have the same non-Cu Jc at 4.2 K, 16 T (e.g., 1500 A/mm2), then the non-Cu Jc and magnetization (for the same deff) of an APC conductor is only 50% or less relative to an RRP® conductor at 1 T. This is because APC strands have much flatter Jc-B curves than standard Nb3Sn due to the point pinning behavior (as a result of the nano oxide particles).
APC Nb3Sn wires are made using an internal oxidation process to create ZrO2 or HfO2 nanoparticles during diffusional growth of Nb3Sn. These particles introduce a second pinning mechanism, as well as refine the grain size, strengthening the grain-boundary pinning above that in non-oxidized Nb3Sn. The two mechanisms taken together increase the flux pinning force Fp, and also shift the peak pinning force to higher field, increasing the Jc at high fields while suppressing the magnetization at low fields. The nanoparticles form at the interface between the Nb3Sn and the Nb alloy, and these particles get trapped as the interface progresses. The particles then grow over the remaining heat treatment time via diffusion of the solutes through the Nb3Sn. The size and size distribution of the nanoparticles has been characterized through image analysis of transmission electron micrographs. A phase field model has been created which uses known thermodynamic and kinetic properties of the component materials to model the nucleation and growth process. Combining the model with microscopy allows evaluation of the effect of heat treatment temperature and explanation of the different nanoparticle sizes seen when the oxidizing element is Hf vs. Zr. This model will aid in the optimization of strand design and heat treatment for high field magnets.
It is very desirable to reduce the long training for Nb3Sn magnets. Increasing the specific heat (Cp) of Nb3Sn conductors can significantly increase their energy margin, and thus may be a promising approach to reduce the magnet training. We developed a design to add high-Cp materials into Nb3Sn strands in 2017, which is compatible with standard Nb3Sn wire production process, and this design does not affect Nb3Sn conductor Je. Here we report our recent progress in the development of such high-Cp Nb3Sn strands toward magnet-grade conductors. By optimizing strand design (e.g., positioning of the high-Cp filaments in the strands, recipe of the high-Cp filaments, and selection of the high-Cp materials), presently strands with excellent drawability and significant Cp increase can be routinely produced. Long-length high-Cp wires are being fabricated. Finally the plan to build model coils using such conductors to investigate the effect on magnet training will be discussed.
Currently, the record critical current density (Jc) achieved in Bi-2212 short samples is around 9600 A/mm¬2 at 5 T in 4.2 K. However, even this very high Jc is still less than 1% of the depairing current density (Jd) of Bi-2212. The 1% Jc/Jd value in Bi-2212 suggests that the long-range filament connectivity in Bi-2212 is rather poor. There are multiple intrinsic and extrinsic factors that can impact filament connectivity in superconducting wires. One of them is irregularities in filament cross-sectional area along the length of the wire. Here we report on wire drawing and heat-treatment-induced area variation along the length of individual filaments that may limit Jc in Bi-2212. Using progressive polishing and image analysis, we observed significant filament size variation, referred to as sausaging, along the length of as-drawn wire that developed during wire drawing. The degree of sausaging increased with the decreasing filament diameter, leading to a filament area variation of individual filaments up to 50%, which may have a negative impact on Jc. Using a special sparse filament 27x18 Bi-2212 wire, we observed that the degree of sausaging in individual filaments increased with increasing time that the wire was in the melt state during the overpressure heat treatment (OPHT) due to Rayleigh instability. Our results show that this heat treatment-induced area fluctuation is more severe for smaller filaments and at long times in the melt can lead to pinch off of individual filaments.
This work was supported by the U.S. DOE Office of High Energy Physics under Grant DE-SC0010421, by the NHMFL NSF under Award DMR- 2128556, and by the State of Florida, and is performed under the purview of the U.S. Magnet Development Program (MDP).
Superconducting magnets equipped with the persistent current circuit have been extensively used for NMR and MRI systems with high resolution cooled by liquid helium. In those systems, superconducting joints with very low joint resistance are essential for realization of the closed circuit. However, practical superconducting joints connecting HTS tapes have never been developed mainly due to the intergrain weak-link problem. For this issue, a remarkable progress in superconducting joint technologies between RE123 coated conductors (RE123) [1] opened a new window toward development of persistent current HTS magnets. In this case, an epitaxially grown intermediate RE123 layer strongly connects the bi-axially oriented RE123 layer of the coated conductors.
On the other hand, Fabrication of superconducting joint between Bi2223 multi-filamentary tapes due to intrinsic characteristics of the material, such as large electromagnetic anisotropy, very short coherence length, which result in weak-links at grain boundaries, and high crystallinity, i.e., poor reactivity of Bi2223 filaments, thus far. Our previous studies on polycrystalline Bi2223 thick films [2,3] revealed that c-axis grain orientation, densification, using precursor composed of large amount Bi2223 calcined powder and small amount of Bi2223 powder, sintering under relatively low partial pressure of oxygen ~3 kPa and increase in Pb concentration are confirmed to be effective guidelines to achieve high intergrain Jc up to ~7 kAcm-2 at 77 K. In addition, precise polishing with very low angle for multi filamentary Bi2223 tapes was found to expose most of the filaments in Bi2223 tapes. Combining these results and technology, we succeeded in the development of high Ic superconducting joints connecting Bi2223 tapes via Bi2223 polycrystalline thick film layer[4]. Introduction of intermediate pressing and optimizations of chemical composition of the thick film layer and heat-treatment conditions improved joint Ic above 100 A at 77 K under self-field. Furthermore, high Ic superconducting joints have been recently developed for reinforced Bi2223 tapes sandwiched by soldered high strength Ni-alloy thin tapes (DI-BSCCO Type HT-NX). Since Sn in solder easily react with Ag forming Ag-Sn alloy and/or intermetallic compound such as Ag3Sn above ~200°C, complete removal of Sn is quite important before fabrication of the joint. Through optimization of each process, joint Ic values above 100 A at 77 K and 300 A at 4.2 K in 3 T were achieved. Including results of current decay measurement performed for loop samples at various temperatures and external fields, potential of superconducting joints connecting Bi2223 tapes and their future prospects will be discussed.
Acknowledgement: This work is partly supported by JST-MIRAI Program, JPMJMI17A2, Japan.
References:
1. K. Ohki et al., Supercond. Sci. Technol. 30 115017 (2017).
2. Y. Takeda, et al., Physica C 534, 9–12 (2017).
3. Y. Takeda et al., Supercond. Sci. Technol. 31, 074002 (2018).
4. Y. Takeda et al., Appl. Phys. Express 12, 023003 (2019).
The Japanese team, centered on Kyushu University, is developing a high-temperature superconducting propulsion system for aircraft, taking advantage of its strengths such as low AC loss technology. One of its features is that the motor and generator are developed as fully superconducting rotating machines, which consist of superconducting windings for both field and armature coils. Next, overwhelming thermal stability is being aimed for by realizing high-temperature operation in liquid nitrogen by taking advantage of the characteristics of high-performance wires. In addition to adopting a heat exchange method that uses a low-temperature refrigerant instead of a refrigerator, the heat insulation structure has been greatly improved to reduce the weight of the rotating machine.
First, in FY2019, we succeeded in making a prototype of a fully superconducting motor with a small capacity of 1 kW, confirmed that it was able to show the specified performance, and realized a demonstration of moving the motor on rails by connecting a fan.
After that, a large-scale project started from FY2019 in Japan, and while developing various elemental technologies, we are trying to manufacture a large 500kW-class motor while reflecting the results. Recently, the 500kW-class fully superconducting motor was successfully made, and it is put in the evaluation stage. At least, some rotation was confirmed although it is not enough. Now, the initial defects found in the above evaluation are being repaired, and after completing these, we are planning to conduct a full-scale performance evaluation. Furthermore, an operation test in a low-temperature, low-pressure environment that simulates the flight environment is also planned.
This work is based on results obtained from a project commissioned by NEDO and METI.
An overview of the “IZEA” NASA University Leadership Initiative (ULI) will be presented to provide context for several other presentations describing details and progress under specific ULI tasks. IZEA addresses removal of carbon emissions for regional aircraft with ~120 passengers, 5000 km range, cruise speed of mach 0.8, and total power 25 MW by using liquid hydrogen fuel. Design of low-loss hydrogen tanks and other factors such as noise reduction motivate consideration of blended wing-body airframes with distributed electric propulsors, which is a significant departure from the present fleet. Primary power is envisioned to come from a 20 MW turbo-electric generator, and cruise power from 10 MW of distributed PEM fuel cells with high-altitude power boost from an oxygen supply to reach 5 kW/kg. The availability of cryogenics permits consideration of superconducting power systems operating at 20–70 K, including a generator, superconducting trunk and distribution lines. Propulsion will connect SiC power controls with novel axial flux motors that incorporate multiple stators tailored for the different mission segments of flight. Motors use conventional magnets and can be adapted to half-superconducting designs. The use of PEM fuel cells requires consideration of a 5 MW cooling system to maintain a ~10°C temperature window around the 30°C temperature of operation. The combined application of several temperature zones, from cryogenic to above 300 K, provides opportunities to optimize the thermal management and efficiency via modification of the airframe and component integration.
Acknowledgements: The authors would like to acknowledge the support from NASA under Grant 80NSSC22M0068. The research was conducted at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1644779 and the State of Florida.
Turboelectric distributed propulsion (TeDP) is one concept which has been explored in the development of all electric aircraft. TeDP allows for the motor and generators to be decoupled from one another and connected through a DC cable distribution network. This enables various airframes to be explored such as the blended wing body (BWB) which allows for greater aero dynamical performance compared to conventional aircraft. For TeDP to be feasible for BWB and other aircraft frames high power density targets have been set. The ambitious power density targets required for large-scale electric aircraft are amenable to superconducting power device such as generators, motors and cables. To achieve the required power density of the power system in a safe and reliable manner requires consideration on the topology, devices, and integration of the necessary cryogenic environment for superconducting technology. Designing the electrical power system without concurrently designing the cryogenic infrastructure has the potential to cause significant interruption to the power system in the event of cryogenic failure. As part of our continued research into superconducting power cables for electric aircraft as part of the NASA University Leadership initiative - IZEA we are assessing the power design and how to develop a resilient DC superconducting bus in the event of failure within the cryogenic system. As part of this study we will perform a review of previously developed DC Superconducting bus topologies for aviation application and assess the suitability in the event of cryogenic failure. This analysis will also provide consideration if superconducting or non-superconducting technology is utilized as part of the motor drive.
We will also provide consideration on the notional power system we are developing as part of the IZEA for a 20 MW BWB all electric aircraft. As part of the power system we consider the aircraft having two superconducting generators and eight superconducting motors. As part of the presented work we will explore strategies to ensure each generator is connected to each motor to increase the resiliency of the power system. We will also discuss the HTS cable topology being developed with the associated termination to the motor drive. This analysis will include commentary on cryostat selection for the HTS cables and the associated volumetric and spatial constraint of installing the DC superconducting buses with the IZEA airframe.
The growth in the aviation sector has highlighted the need to decrease carbon emissions, a significant factor in climate change. Hydrogen is a potential alternative fuel due to its high energy density, and its combustion mostly results in water. The use of hydrogen fuel cells further eliminates nitrogen oxides emissions, making hydrogen a zero-emission energy source. However, due to its low volumetric energy density, it is desirable to store hydrogen in liquid form at about 20 K. The low temperature of liquid hydrogen presents challenges in its storage and transfer, but the cooling power it provides enables the use of superconducting components in the power system, reducing power loss, increasing power density, and increasing overall efficiency. As a collaborative effort in developing integrated zero emission aviation (IZEA, a NASA ULI), we present the design concept for a liquid hydrogen storage system for short-range aircraft with a gravimetric index greater than 0.6. Our design leverages the cryogenic cooling power of liquid hydrogen to support the temperature of various power system components, such as the high-temperature superconducting (HTS) generator, HTS motor, DC power distribution cable network, and power electronic converters. By controlling the pressure in the storage tank, we demonstrate that it is feasible to deliver the desired mass flow rate of hydrogen while effectively cooling the power system components using practical heat exchangers. This work represents a significant advancement towards developing the complete IZEA thermal management system.
Superconducting electric motors offer the potential for low weight and high power in applications such as electric aircraft and high speed marine transport. Combined with renewably-sourced cryogenic fuels and advanced fuel cells they offer a path to zero-carbon mass transport. The proposed architectures of these extreme machines, operating at temperatures around 20K to 50K and employing very high alternating magnetic fields, require materials for the stator that are not electrically conducting and at the same time have good cryogenic structural performance.
Additively manufactured polymers can play a key role in these designs, and a collaboration between the Robinson Research Institute and AUT is studying the performance of a range of composite polymers in superconducting machine applications. There are significant challenges to be met, including understanding the effect of the build process on material properties at low temperatures, and also the effect of formulation changes on thermal properties.
Additively manufactured metals can be employed in the rotor components, where the magnetic field fluctuations are very small for our synchronous designs. In this usage case, we can achieve dramatic reductions in the weight of the rotor assembly by minimising the number of joints and facilitating the design of multi-functional components in our helium cooled, vacuum cryostat architecture.
The performance requirements for a number of key components in our prototype machines are discussed along with cryogenic testing results for selected additively manufactured materials and composites.
Electric propulsion is one way of making low emission flying possible. To do so, they must be particularly lightweight and have a high efficiency, at least as good as current systems such as gas turbines or turboprop engines. In order to reduce the impact of global transport on the environment and pollutant emissions, a revision of current systems is necessary and expedient. Because of its high energy density, cryogenic liquid hydrogen can be used in combination with fuel cells both as an efficient supplier of energy and for effective cooling of the electric motor. The development of this system concept is the subject of the "AdHyBau" research project, of which the authors are part of the consortium. The basic system architecture of the hybrid electric powertrain was presented by partners here [1]. A DAHER TBM850 was used as a reference. This application scenario results in extremely different temperatures in different areas of the electric motor at different operating points. In addition, electrical contact and the flow of gaseous hydrogen pose special challenges. Not to be forgotten are the mechanical demands on the motor in terms of power, torque and speed.
This paper presents the engineering design process and the resulting concept for such an electric engine. After the development of the concept for the rotor was presented here [2], the development of the concept for the stator is discussed here.
The development of the concept for the rotor has been presented here [2]. Based on the requirement classes mentioned in [1], the concrete requirements resulting from flight operation and the approach of cooling with cryogenic gaseous hydrogen are first compiled. Then, the selected electrical concept of a 500 kW engine is presented, which serves as a basis for identifying the required components and their arrangement. Compared to conventional electric motors, additional components are required. These include hollow coils, structures to distribute the cold gaseous hydrogen to the coils and elements to support the stator laminations with the coils. Materials are then selected for these components with the aim of minimizing weight, and their geometries are predimensioned using analytical approaches and numerical methods. Finally, the individual concepts are synthesized into an overall concept.
The result is a compact design for a cryogenically cooled electric motor with a power density of more than 10 kW/kg and a mass of less than 50 kg.
The authors gratefully acknowledge the financial support of the BMWK within the LuFo project "AdHyBau" (20M1904C) and the support in design and simulation by Linus Tönnishoff.
Literature
[1] Vietze M, Weiland S, System analysis and requirements derivation of a hydrogen-electric aircraft powertrain, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2022.09.052
[2] M. Pohl et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1226 012077, https://doi.org/10.1088/1757-899X/1226/1/012077
The aviation industry is responsible for a small but rapidly growing proportion of the world’s greenhouse gas emissions. One way to ameliorate this problem is by replacing hydrocarbon-based propulsion systems with electric propulsion systems. This approach requires storing energy in the form of batteries or liquid hydrogen. For large, commercial aircraft, batteries are currently untenable due to their relatively low power density. Hence, the Center for High-Efficiency Electric Technologies for Aircraft (CHEETA) is researching technologies needed for an all-electric commercial airplane with liquid hydrogen (LH2) energy storage. One key enabling technology is superconducting electric propulsion motors. In the CHEETA airplane, the cryogenic LH2 fuel could function as a coolant for the motors’ superconducting components. Such motors have the potential to achieve high specific power and efficiency, though many technical challenges need to be overcome to achieve a practical design. These include ac losses in the superconducting armature winding, two phase cooling with liquid hydrogen, and fault handling and protection. Here we present a status update on the design and risk-reduction tests for a fully superconducting aircraft propulsion motor, as well as a broader project overview.
The exciting history of the search for and study of high-temperature superconductivity (HTS) with Tc above 77 K (~1987-2023) and room-temperature superconductivity (RTS) with Tc above 200 K (~2005-2023) will be briefly reviewed, and the impressive achievements in these two periods will be summarized. The promises and challenges that will enable HTS and RTS to change the world as envisioned will be presented and critically discussed.
Research was supported in part by the U.S. Air Force Office of Scientific Research Grants No. FA9550-15-1-0236 and No. FA9550-20-1-0068, the T. L. L. Temple Foundation, the John J. and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston.
https://www.cec-icmc.org/2023/awards/
Superconducting nanowire single photon detectors (SNSPDs) offer unparalleled efficiency, minimal dark count rates, and picosecond jitter, making them ideal for single photon detector applications across the visible to mid-IR spectrum. A common cryogenic system used to reach these detectors' optimal operating temperatures (>1 K) consists of a Sumitomo's compact RDK101 Gifford McMahon Cryocooler (GMC) running on an Zephyr air cooled compressor, coupled with a 4He adsorption stage. In this work, we provide measurements of the RDK101 GMC second stage regenerator tube cooling power at several locations along its length. We then characterise the performance of the adsorption cooler with heat loads applied to the regenerator tube. Our measurements indicate that heat loads of 1.2 W can be intercepted at the tube's section near the GMC's first cooling stage, with negligible adsorption cooler performance degradation. The thermal conductivity of yellow brass coaxial was characterised from 4 K to 50 K. Here we show that the heat load from 64 coaxial cables can be optimally intercepted with the defined regenerator cooling power. These results demonstrate that a 1024-pixel SNSPD array using a 32x32 row column multiplexing architecture can be successfully implemented in this cryogenic platform.
Applications of very low temperature cryogenics are growing to serve the needs of quantum electronics and basic science. The evolution of these applications to larger and more powerful systems involves more cryogenic cooling power. The architectures, techniques and machines of current refrigerators do not allow this scale up (power, efficency).
Air Liquide Advanced Technologies wishes to address this problem with its current product range of “HELIAL” Helium liquefiers delivering cooling power of the first cooling stages of the dilution fridges.
The Colossus platform at Fermilab will be the largest and most powerful 3He/4He dilution-cooled cryogenic system constructed to-date. Perhaps its primary innovation will be in the integration of a liquid helium cryogenics plant to cool the stages typically cooled by mechanical cryocoolers in commercially available cryogen-free dilution refrigerators. This design shift carries with it important implications for the future of cryogenics associated with quantum computing due to the inherently greater efficiencies of helium cryogenic plants when compared to the use of multitude of independent mechanical cryocoolers. Construction of Colossus is expected to begin in 2023 with a target of commencing operations in 2025.
Colossus will be a large millikelvin platform that will have a two-meter diameter mixing chamber plate. This uniquely large millikelvin platform will utilize a cryogenics plant to maintain progressively lower temperatures at each of the three upper stages and precool the lower three stages of the system. At the millikelvin stages, Colossus will employ multiple commercially available dilution units to achieve millikelvin temperatures at the intermediate cold plate and mixing chamber stages. The incoming helium-3/helum-4 process fluid mixture for each dilution unit will flow through tubes wrapped around copper posts attached to each of the upper stages of the system. These tubes will function as capillary heat exchanger to reduce the temperature of the incoming helium mixture to the appropriate temperature at each stage.
The microwave signals used to control the qubit states need to be virtually free of noise and any electrical disturbance, so they must be carefully filtered before the microwave signals reach the sensitive quantum processor. In consideration of the requirement of miniaturization, we present a development of miniaturized multiplexers for a quantum computer. A high temperature superconducting (HTS) multiplexer is designed based on common-coupled resonator structure according to coupling matrix synthesis method. The theoretical result, coupling matrix, and the simulated result have also been demonstrated. The simulated 3 dB passbands of the multiplexer are 6.64-6.7 GHz, 6.82-6.9 GHz, 7.03-7.085 GHz and 7.22-7.26 GHz respectively, the simulated return losses is better than 15dB in all the pass bands. Besides, the coupled property of resonators is also analyzed and presented in this paper. There is good agreement between the simulated results and theoretical analysis.
This article presents a novel high-temperature superconducting (HTS) dual-band bandpass filter using quadruple-mode resonator. The quadruple-mode resonator consists of one square ring resonator and two open-stubs. Through odd- and even-mode method, two even-mode frequencies of the proposed resonator can be independently controlled by two open-stubs compared with ordinary square ring resonator. Therefore, the degree of freedom of design is increased, which can meet the requirements of rapid design of multi-band bandpass filters. The filter has a compact size and the two passbands is centered at 1.8/2.4 GHz. The simulated results show that the return loss is better than 20 dB in both passbands and are consistent with the expected objective. It shows that the proposed scheme is feasible and can provide design reference for other multi-band bandpass filter designs.
An ANL-SLAC collaboration is working on a design of a planar superconducting undulator (SCU) demonstrator to be tested at SLAC Free Electron Laser (FEL). The demonstrator cryostat is multi-segmented, and each segment includes a ~1.5-m-long superconducting undulator as well as other magnetic components like a phase shifter and a beam position monitor (BPM). This LHe-based cryostat is cooled by two stage pulse tube cryocoolers (Cryomech PT425). A detailed load map of the cryocooler was measured and bench marked with the manufacturer’s load map. A thermal model of one segment of the cryostat which includes all cooling circuits has been created in ANSYS and analyzed using the measured cryocooler load map. This paper presents the calculated cooling power requirement and the temperatures in the cryostat.
We have been studied a magnetic levitation system which is constructed of a high temperature superconducting (HTS) coil, a HTS bulk, and an iron rail. The levitation force is generated by using bending of magnetic flux lines due to a magnetic shielding effect of the HTS bulk. In our former works, we constructed desktop-size experimental arrangement, demonstrated the levitation properties, and analyzed numerically some variations of the HTS coils such as a racetrack coil.
Our next step is scale-up of the levitation system for supposing a real-size vehicle. To support about 30 tons of the vehicle weight with the 4 levitation systems mounted at the 4 corners of the body, it is necessary to generate 7.5 tons of the levitation force by each levitation system. We designed a large-scale system that scaled up the size of the HTS racetrack coil, the HTS bulk, and the iron rail in the desk-top size system by a factor of 10, and numerically estimated the levitation properties. The typical size of the racetrack coil is that the inner and outer diameters are 60 and 100 cm respectively, the height is 10 cm, and the straight section is 200 to 300 cm. According to the simulation results, the large-scale system generated approximately 5 to 10 cm of a levitation gap between the body and the rail, and over 10 tons of the levitation force in each system.
In conclusion, sum of levitation forces generated by the 4 systems mounted at the corners of the body becomes over 40 tons; hence we think the large-scale system have enough force to levitate the real-size vehicle.
Following the first successful demonstration of accelerating gradients up to 10 MV/m on a conduction-cooled 650 MHz SRF cavity in 2020, Fermilab has embarked on the design and construction of a compact SRF e-beam accelerator based on this novel cavity cryocooling technique. This accelerator will deliver a 1.6 MeV, 20 kW electron beam and is poised to be used for industrial applications such as medical device sterilization. The design of the accelerator is complete and presently the accelerator is in the construction phase. This contribution will showcase for the first time the key cryogenic features of the compact accelerator including the conduction cooled SRF cavity, integrated thermionic electron source, low-heat leak power coupler, all housed within a thermally and magnetically shielded cryostat. Plans for commissioning the accelerator as well as next steps for upgrading to a ~8 MeV, 200 kW e-beam machine will also be discussed.
Acknowledgement: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
As a crucial component of carbon capture, utilization and storage (CCUS) projects, CO2 transport makes sense for expanding the scale of CO2 utilization. And CO2 liquefaction is significant to ensure transportation safety and improve efficiency. In the demand for long-distance transport on the sea, using ship instead of pipeline is considered more competitive. Aiming at the temperature and pressure required for ship transport, this paper studies four liquefaction schemes including the compression refrigeration system, the Linde Hampson system, the precooled Linde Hampson system and the Claude system. The thermodynamic and exergetic ananlysis models are established primarily and then the relevant design parameters are determined through simulations and optimizations by HYSYS software. Total power consumption, liquefaction efficiency and exergetic efficiency of the four systems are calculated and compared. The precooled Linde Hampson system shows the best performance with the three indicators of 391.74kJ/kg, 97.97% and 55.86%, respectively. Additionally, exergy destruction among the system components are analyzed for Linde Hampson system and precooled Linde Hampson system. The maximum exergy destruction stem is form compressors. And the proportion of the total exergy destruction with J-T valves are 19.38% and 2.63%, respectively. Furthermore, the replacement of the J-T valve by a liquid expander is studied. For these two systems, 9.35% and 0.94% of the power consumption could be reduced. The pressure drop before and after the J-T valve directly determines the effect of this change. The research results could provide some vital reference for choosing proper CO2 liquefaction methods and reducing energy consumption during the process.
In current industrial production, compressed air has many industrial uses and is widely used in the petroleum, chemical, metallurgical, and power industries, playing a vital role. Normally, compressed air is produced directly through electrically-driven compressors, but the electricity market is gradually changing. As more renewable energy sources are integrated into the grid, the peak-to-valley electricity price differential will increase further. Direct compressed air production for uninterrupted industrial production is becoming increasingly uneconomical. In this paper, a novel compressed air supply (CAS) system is proposed based on cryogenic energy storage (CES), utilizing the solid-phase packed bed for high-grade CES, and compressed heat is used for domestic hot water supply. During the valley period, the air is compressed by compressors and liquefied by the packed bed, and in the peak period, the liquid air is vaporized to release the cold energy and regulated to a certain pressure for industrial use. The thermodynamic analysis and economic analysis of the system are carried out to determine the optimal configuration and to demonstrate the excellent economic benefits of the system. The significant potential of this concept in the current electricity market is further analyzed.
Thermodynamic refrigeration cycles are designed and optimized for the emerging application to high-field HTS magnet systems at 20 K, such as fusion, NMR, or large accelerators. The refrigeration requirements are specified as the forced-flow cooling of HTS magnets at 20 K, a thermal shield at 100 K, and current leads from 50 K up to ambient temperature. The current leads are a serial combination of metallic conductors (as warm part) and REBCO tapes (as cold part), but only the metallic conductors are gas-cooled. In order to design a fully closed system without any supply of liquid nitrogen or boil-off loss, standard or modified Brayton refrigeration cycles are proposed to be thermally coupled with a circulation loop for forced-flow cooling. Since gaseous helium is used as refrigerant and coolant at the same time, an integrated design of refrigeration cycle and cooling loop is also proposed. The proposed cycles are optimized for the best thermodynamic performance with iterative analysis with process simulator (Aspen HYSYS) and real-gas properties. It is rigorously verified that the optimized cycles can achieve a great thermodynamic efficiency. Details of various cycles are presented and discussed towards the practical development.
This work is supported by a Korean governmental R&D (research and development) project under the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (2022M3I9A1076800).
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) operates the Central Helium Liquefier (CHL) to provide 2K helium refrigeration to the superconducting radio frequency (SCRF) cavities in the linear accelerator (LINAC). To maintain the purity of the helium, the CHL operates a LN2 cooled, dual-bed purifier. This purifier was purchased as a refurbished unit during the construction of SNS about 20 years ago. The current operational issues with the existing purifier will be discussed. The procurement, fabrication status and commissioning plans will also be discussed.
Constant ingress of impurities in Muon Campus g-2 experiment at Fermilab has resulted in reduction of efficiency of cryogenic expanders and occasional undesired downtime to flush the impurities. Due to insufficiency of current 60 g/s mobile purifier, a full flow purifier is designed to be used in Muon Campus which purifies 240 g/s of Helium throughput of 4 compressors through charcoal bed at 80 K and returns ambient Helium back to the system. The purifier is designed to be operated near liquid Nitrogen temperature during cold operations and up to 400 K during regeneration. Both warm and cold operational range of the purifier has required use of appropriate clearances in design due to expansion and contraction. The purifier of around 16 ft height which is designed to be operated vertically is to be shipped horizontally. The asymmetrical position of heavy stainless steel heat exchanger in the purifier support frame and 5g vertical load design consideration for shipping has required use of shipping supports and heat exchanger rotational stops to comply with design requirements. Finite Element Analysis (FEA) of purifier system is performed in cold, warm and shipping cases to verify that the purifier satisfies the design requirements.
The future operation of the 4 kW 15 Kelvin MOLLER experiment at Jefferson lab necessitates an increase of cryogenic capacity at the End Station Refrigerator. The current plant is the former 1.5 kW (4.5 K) ESCAR plant that has been operating at Jefferson Lab since 1994. The existing 1.5 kW plant is not able to support the load for MOLLER and will be replaced with a refurbished plant comprised of the cold box and compressors of the 4 kW ASST-A plant from the Superconducting Super Collider in Texas. This paper outlines the assembly, repair and modifications made to the cold box, along with the design of the plant as a whole and its integration into the existing distribution system.
In order to develop higher power density motors and generators for aircraft applications, the higher magnetic field generated by stators is needed to create larger torque. The current density of conductors of stators should also be higher to generate a large magnetic field. Therefore, cryogenic liquid cooling for stators is needed to prevent overheating problems. The Ohio State University developed a demo one slot of a stator. This slot was constructed using two aluminum bars with a cooling slot between them. These two aluminum bars were made of 1100 commercial purity Al alloy. The two bars were placed in parallel with a 1.6 mm gap in between, which acted as a flow channel for the cryogenic coolants. And these two bars were connected in series and carried a maximum current of up to 90 A/mm^2. The coolant (LN2) was continuously flowing through the channel while the aluminum conductors were carrying a high density of current. Thermocouples were used to capture the temperature data during the experiment every second. This work was compared to FEM modelling, where the heat transfer coefficient of two-phase transition cooling (both nucleate boiling and film boiling) was calculated by these data of temperature and current. Our analysis shows that this approach to stator cooling is able to meet the requirements of the cryogenic stator design.
Abstract The PIP-II Cryogenic Distribution System (CDS) connects the helium plant to the superconducting linac consisting of 23 cryomodules. The regulation of the helium stream flowing by the PIP-II CDS is carried out by means of control valves located in the Distribution Valve Box. The cryomodules are supplied of helium from individual Bayonet Cans. The entire CDS process lines are shielded from the thermal radiation from the ambient vacuum jacket by actively cooled thermal shields. High efficiency of the thermal shield has been achieved by state-of-the-art optimization of its thermalization system consisting of thermal bridges connecting the shield to the high temperature helium return pipe nominally at 80 K. The temperature and stress analyses of the thermal shield has been performed numerically. The analyses results obtained on the case of the thermal shield for PIP-II CDS Distribution Valve Box are compared with the solutions applied in other Big Science cryogenic machines.
Acknowledgement
This abstract has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Exergy analysis was applied to the evaluation of helium internal purifier in this paper. The important operating parameters has been given to determine the exergy destructions in components as well as in the entire cycle of internal purifier. The analysis results show that the recovery of liquefied air energy can improve the performance of purifier and the exergy destruction of different heat exchanger is different. Results from the analysis helped evolving guidelines for designing appropriate technological process for practical helium internal purifier. An internal purifier with an optimized structure was designed to remove air impurities up to 10 mol%, beyond previous maximum impurity content. The impact on liquefaction capacity is minimized because of the small consumption of cold flow. The achievable performance were also provided in this paper. The purifier could remove air impurities up to 8 mol%.
Abstract：In order to investigate the heat transfer mechanism of helium-based pulsating heat pipe, a two-dimensional numerical model of a four-turn helium-based pulsating heat pipe was developed. The model was numerically solved based on the Volume of Fluid (VOF) method, and the initial state and operating state of the helium-based pulsating heat pipe were simulated. The initial state is a saturated static state with alternate distribution of vapor plug and liquid slug. The running state is the pulsating flow with changing direction, and the flow type is the plug flow. The flow and heat transfer characteristics of the helium-based pulsating heat pipe were analyzed and compared with the actual experimental results.
The specific heat of helium rises rapidly below 20 K, resulting in increased loss of the regenerator. The adsorption regenerator using the adsorbed helium as the regenerator material is the effective method to improve the performance of 4 K cryocoolers. In this paper, we use Grand Canonical Monte Carlo method to simulate the adsorption of helium on the MOF-5 below 20 K, and the effect of temperature, pressure and other parameters on the adsorption amount was analyzed. By comparing the adsorption characteristics of activated carbon to helium, the application potential of activated carbon and MOF-5 in regenerator was studied.
Modeling of condensation of gases including O2 and CH4, in the presence of high concentrations of noncondensables, is needed for the design and analysis of ISRU systems. The objective of this study is to provide the Generalized Fluid System Simulation Program (GFSSP) computer code with the capability of scoping analysis of condensation in the presence of noncondensables in internal flow systems. Condensation in the presence of noncondensables is modeled using the Couette flow film (stagnant film) model. Experimental data on the condensation of water vapor in downward flow of air-water vapor and helium-water vapor mixtures in vertical tubes are compared with the predictions of GFSSP. The comparisons show that with the implemented capability GFSSP can predict the experimental data well.
In order to improve the heat transfer and pressure drop performance of plate-fin heat exchanger in helium cryogenic system, a new type of perforated-serrated fin is proposed by combining traditional serrated and perforated fins. A series of numerical simulations are carried out with well-validated 3D models. Because the flow in the channel should be in a turbulent state, the RNG k-ε turbulence model is used which can simulate the strong strain flow with higher accuracy. The numerical model of flow and heat transfer in the fin channels takes into account the influence of low temperature conditions with variable physical properties by NIST-Real-Gas-Model invoking the properties of helium. Meanwhile, three performance evaluation criteria Colburn factor j, friction factor f and JF-factor are used to qualitatively compare their pressure drop, heat transfer performance and thermo-hydraulic performance. The results show that the heat transfer performance of new perforated-serrated fins is better. Colburn factor j of the new fins increases by 10.74%~21.40% compared with serrated fin. The flow performance of the perforated-serrated fin is slightly worse, but the overall thermo-hydraulic performance is better, especially at low Reynold number. In addition, the effects of various structural parameters on the thermohydraulic characteristics of the perforated-serrated is obtained. The present work might be very helpful to enhance the performance of heat transfer in the fin channels and also guide the optimum design of plate-fin heat exchangers in helium cryogenic system.
The recuperative heat exchanger is a key component of the new pulse tube expansion type cryogenic refrigerator, which is tasked with the periodic heat exchange of cold and hot helium, and the thermodynamic efficiency of the entire machine is directly impacted by its heat exchange efficiency. A simulation study is carried out to investigate the heat transfer characteristics of the intermittent alternating flow recuperative heat exchanger by modeling a heat exchanger unit. The instantaneous heat transfer characteristics in the intermittent alternating flow cycle with different wall materials and different inlet mass flow rates of hot and cold fluids are analyzed. The results show that the performance of the heat exchanger is significantly influenced by the wall material and mass flow rate and the heat transfer characteristics are much different between the heating and cooling processes of the mass during the acceleration and deceleration of the alternating flow.
The cryogenic heat sink attached to the cold head of the cryogenic cooler is used to cool cryogenic fluids such as helium, neon, and hydrogen. The performance of the heat sink involves the pressure drop, the heat transfer area, and the overall size. In order to improve the thermal-hydraulic performance of the heat sink within a limited size, it is necessary to reduce the pressure drop and increase the heat transfer area of the heat sink. Airfoil-shaped fins are known to show less pressure drop while keeping good heat transfer characteristics. In this study, the thermal-hydraulic performance of the heat sink is investigated for the various configurations of the fins using computational fluid dynamics (CFD) analysis. The average friction coefficient and heat transfer coefficient are calculated to select the most appropriate heat sinks with overall dimensions of 50 mm width, 50 mm length, and 20 mm height. Although the CFD simulation result shows superior thermal-hydraulic performance compared to the heat sink manufactured by conventional machining processing, the designed heat sink is fabricated using powder bed fusion (PBF) metal 3D printing due to its fine pin structure. An experiment is conducted to evaluate the performance of the heat sink using a characteristic evaluation apparatus including a cryogenic blower and a cryocooler. The airfoil heat sink is tested at a maximum mass flow rate of 30 g/s, a maximum pressure of 5 bar, and a temperature range of 20 to 60 K.
The self-pressurization and pressure control in a zero boil off tank partially filled with liquid nitrogen is investigated numerically. This research analyzes the influence of phase change and forms of the heat exchanger for cryogenic liquid storage in zero boil of tank using numerical method. The phase change model in simulation comes from the Schrage equation which to describe the mass transfer that occurred in the tank and several different accommodation coefficients derived from the equation are used to simulate the case. Two kinds of different heat exchanger that conduct the refrigeration power in zero boil off tank are compared the effects in reducing thermal stratification and controlling the pressure. Results show that the accommodation coefficients in phase change model has a big influence on the cryogenic liquid storage in zero boil off tank and there exists a magnitude about 10-5 which is proper to describe the evaporation and condensation in the tank. Two kinds of heat exchanger can reduce the thermal stratification and the pressure but the one whose fin attach the inner wall of the tank is more effectively.
A novel gas thermal switch is designed and tested in this paper. This thermal switch would be considerably useful in the cryogenic devices with cryocooler, especially for the helium free devices. It can cut off the conduction path with a simple and low cost design. It has an active operation mechanism driven by normal gas. The fine calculated switch gas type and amount can drive the thermal switch off with the instinctive heat load through CH itself.
A test rig with this thermal switch is built and several tests are conducted to verify the performance. The design principle and the test results will be presented in this paper.
Heat switches are widely used in cryogenic systems and play an important role in controlling thermodynamic cycles and accelerating the cooling of cryogenic components, etc. Among them, the active gas-gap heat switch (AGGHS), as one of the mainstream heat switches, mostly uses activated carbon as the adsorption material. It desorbs/adsorbs helium, by heating/cooling the activated carbon, to realize the on/off state. Normally, a short response time, which is related to adsorption properties of the materials and the heating method of adsorption bed, is desired. In order to further shorten the response time and improve the performance of the heat switch, an active gas-gap heat switch using carbon nanotubes as the adsorption material is investigated. The heat switch at different filling mass of carbon nanotubes and charged amount of helium was tested and compared with the performance of the heat switch using activated carbon.
Noble Liquid Test Facility (NLTF) at Fermilab is dedicated to the research and development of liquid argon neutrino detectors. The liquid argon is provided by a small cryogenic system supplying four cryostats. Multiple modifications of the cryogenic system over the years resulted in limited performance with respect to the liquid argon flow rate. The time required to fill the cryostats has significantly increased with no obvious cause, leading to delays in research efforts. The paper describes the development of the two-phase hydrodynamic model of the cryogenic system, the investigation of parameter sensitivity, and optimization. The optimized model indicates limiting factors and provides recommendations for the upcoming upgrade of the cryogenic system.
A proposed design for the removal of impurities with high electronegativity from liquid argon for the purpose of neutrino detector research is described. The design will utilize a commercially available submersible, cryogenic pump to circulate liquid argon through an external filter containing molecular sieve and activated copper media, removing water and oxygen, respectively. The existing state-of-the-art vapor-driven filter design provides a throughput of 0.5 L/min, while the capacity of the submersible pump design is at least 4 L/min, though potentially greater depending on total losses within the filtration piping assembly. An additional benefit of the new design will be the ability to regenerate the filter media in situ without stopping the experimental testing. The following work will describe the design, operation, and expected performance using CFD analysis.
Hydrogen thermoacoustic instabilities are a relatively unexplored but promising opportunity for cryocooler development. This article describes a new research cryostat developed to investigate hydrogen as a working fluid in thermoacoustic systems. The cryostat is a modular, turbo-molecular pump driven, vacuum chamber with a 4.2 K pulse-tube cryocooler capable of 45 W of cooling at 50 K. To assess the performance of the cryostat, a feasibility study of direct thermoacoustic cooling with ortho-parahydrogen conversion is conducted. An acoustic resonator system is designed to excite acoustic modes via imposed temperature gradient on a porous stack between the ambient environment and cold strap connected to the cryocooler. The generated acoustic waves transfer heat inside of a porous regenerator insert to produce a refrigeration effect at cryogenic temperatures. In addition, the regenerator solid matrix will be catalyzed for ortho-parahydrogen conversion, demonstrating a novel combination of cooling and conversion of cryogenic hydrogen in a single device. Modelling results, design, construction, and performance of the cryostat are reported.
The Leidenfrost effect is a phenomena manifested by a liquid droplet interacting with a surface that is considerably hotter than the boiling point of the droplet resulting in a thin vapor layer separating the droplet-surface pair. This phenomena also occurs between a droplet and a superheated immisible liquid pair, for example a liquid nitrogen droplet in a pool of water. Due to the encapsulation of the droplet in the pool, a bubble of vapor develops around the evaporating droplet. The dynamics of the droplet evaporation and subsequent bubble growth is theoretically and experimentally investigated for a particular case of a small (capillary) droplet. The knowledge developed in this work is of interest in optimizing the cooling processes in pharma and beverage industry.
As a good paramagnetic material with low magnetic ordering temperature, CPA is often used in the study of ADR. A typical ADR consists of a multitude of components such as the salt pill, superconducting magnets, heat switch, etc. To study the performance of CPA in the single-stage ADR, an experimental system had been built. It used a two-stage GM refrigerator to provide ADR with a low-temperature environment of less than 4K. A 1.2K superfluid helium bath was connected to the ADR, and they were controlled by a mechanical heat switch to turn on and off. We have already conducted preliminary experiments, using superconducting power provides a magnetic field. In the first experiment, CPA was pre-cooled to 1.95K, demagnetized from 2T, and the lowest temperature obtained was 460mK. We conducted a second experiment after optimizing structures such as the heat switch and suspension, CPA could be pre-cooled to 1.65K. It was demagnetized from 1T and 2T, respectively, and the lowest temperatures obtained were 359mk and 321mK. Through experiments, we have identified the factors that influence cooling and are further optimizing them in subsequent work.
Advances in 3D printing are disruptive opportunities for material selection and component design in cryogenics. However, thermophysical property measurements for these novel materials are generally unavailable at cryogenic temperatures. This experiment explores the variation in thermal conductivities due to print direction of two aluminium composites (AlSi10Mg and Al6061-RAM). The direct linear heat flow method was utilized to calculate thermal conductivities using a measured wattage input, temperature differential, and Fourier’s Law of Conduction. A multi-measurement linear regression was applied to determine thermal conductivities at fixed average temperatures over the range from 20-100K. The AlSi10Mg composite had a greater thermal conductivity than Al6061-T6 for both printing planes by approximately 230%. The XY-plane print direction resulted in a reduction in thermal conductivity than the Z-plane by approximately 30%. The AL6061-RAM composite had effective thermal conductivities smaller than the machined Al6061-T6 by approximately 70%. The thermal conductivity in the Z-plane print direction was consistently greater than the thermal conductivity in the XY print direction. Validation studies were conducted utilizing Al6061-T6 and SS-304/304L. The calculated deviation for the validation samples depicted a 20% difference from the recommended reference values from the National Institute of Standards and Technologies (NIST). The calculated uncertainty of the experimental system was 5-10%; increasing with decreasing temperature. These preliminary measurements depict the need for further analysis on 3D printed composite materials and reverification of common materials, due to current manufacturing methods improving since the experimental measurements for SS-304/304L and Al6061-T6.
The temperature coefficient of resistivity is a critical element of many AC-based hot-wire measurements of thermal properties. At cryogenic temperatures, most metallic materials suitable for wire and film-based forms have either a temperature coefficient or absolute resistivity that is too small to enable practical, accurate measurements. Invar (36% Ni 64% Fe) controlled thermal expansion alloy has a significant temperature coefficient of resistance while also maintaining significant absolute resistivity at cryogenic temperatures, and so has seen some use in low temperature 3-omega measurements. Prior data on the temperature coefficient of resistivity of invar is limited and the uncertainty is high. In this work, we present high-accuracy resistance and temperature coefficient data for this material from 4-300K.
As part of the energy transition, the off-shore wind power market is booming with many very large-scale projects emerging or already in operation in Europe, Asia and America. Wind farms are commonly made up of several dozen turbines, the power of which has steadily increased in recent years, now exceeding more than 10 MW each, or soon even beyond.
Installed more than 150 meters above the waves, the nacelles housing the electric generators nowaday weigh more than 400 tonnes. This includes in particular the tens of tons of rare earths used in electromagnets that operate at room temperature.
By cooling the electromagnets located in stators or rotors down to cryogenic temperatures, a superconducting state can be achieved, where electrical conductors do not oppose any resistance anymore. The weight of the generator and therefore that of nacelles might then be reduced by several dozen tons, while the mass of necessary rare earths might be reduced by two orders of magnitude.
This poster presents an innovative cryocooling concept using turbomachines that is able to provide about 1 kW of cooling power at 20 Kelvin, up to 4.8 kW at 65 K, enough for cooling a 10 MW-scale wind turbine generator, or any other type of superconducting application. Other versions will operate at 4 K. It is based on Air Liquide’s extensive experience on the mature reverse turbo-Brayton refrigeration technology (from the International Space Station to LNG ship carriers) and on large superconducting systems for scientific instruments (CERN-LHC, ITER, SLAC, etc…).
A compact, hermetic and extremely reliable system, this standalone cooler is composed of a few small turbomachines and heat exchangers mounted on a unique plate. An internal manifold distributes the cold gas to the various magnets using closed loops. The complete system can cool down either stators or be mounted onto a direct drive rotor to rotate with it.
Superconductivity is a mature technology that has recently been demonstrated on the field for wind turbines. With our well suited cryocooler, it will become clear to wind turbine OEMs this will play a critical role, given the numerous wind farms to be built in the near future. This cooler will also address superconducting power transmission cables working up to 65 K or any other type of superconducting application. Notice this highly flexible cooler can also provide cooling power at temperature lower than 20 K with a reduced efficiency.
This makes it a very versatile, flexible and compact cooling system featuring the reliability we can expect from an industrial equipment.
The ITER project is the largest international scientific collaboration aimed at developing fusion energy as a sustainable and clean source of energy. Its magnet system provides the magnetic confinement necessary for fusion reactions to occur and be sustained for long periods of time. The Large Hadron Collider (LHC) is the largest particle accelerator ever built. It consists of a 27 km ring of superconducting magnets and radiofrequency (RF) accelerating cavities. In both cases, High-strength structural materials play a crucial role in ensuring the integrity of the superconducting magnet system operated at cryogenic conditions.
The physical and mechanical properties of high-strength austenitic stainless steels and their importance for the structural integrity of the ITER magnet system are discussed. The rationale for the choice of multi-directionally redundant forged FXM-19 (also known as Nitronic 50) as the primary material for several structural components is explored, to cope with the stringent design requirements. The challenges faced in the steelmaking and processing of the material are also discussed.
Results issued from cryogenic tests on FXM-19 are presented, showing how the unique properties of this grade at cryogenic temperature, namely its high strength, excellent ductility, and high fracture toughness, make it an ideal material for the demanding requirements of the ITER magnet system.
This work shows how the selection of high-strength stainless steels is essential to ensure the safe and reliable operation of high-field superconducting magnets and illustrates how the continued development and optimization of these materials will be critical for the advancement of fusion energy technology but also accelerator magnets.
Nitronic alloys are attractive because they have both good room temperature and cryogenic temperature properties. Austenitic alloys 304 and 316 usually have better ductility and toughness at cryogenic temperatures but they can have low tensile strength at room temperature than Nitronic alloys. US-ITER chose Nitronic 50 for the ITER central solenoid tie plates because they needed good room temperature yield strength to pre-stress the coils at room temperature as well as good low temperature strength and toughness. The cons for Nitronic alloys are they are usually more expensive and they are a more complex alloy with more alloying elements. During fabrication and manufacturing extra care must be taken to ensure the final product with the desired/published properties. A review of past applications where Nitronic alloys were chosen and some case histories where problems were encountered will be presented.
The SPARC tokamak requires large-scale, high-strength cryogenic structures for its toroidal field (TF) coil case. Due to the large electromagnetic forces induced during operation, forged XM-19 was selected as the case material in regions of highest stress. To qualify materials and processes for large forgings, a toroidal field model coil (TFMC) case was produced at relevant SPARC TF scale. A custom alloy chemistry was implemented to maximize strength and fracture toughness properties at cryogenic temperatures and a 20 ton forging with cross section in excess of 350 mm was produced. Heat treatment studies were conducted to determine the effects of solution annealing with air- and water-cooling on precipitate formation and subsequent material properties. Microstructural analysis and tensile testing at 20K found material free of unwanted sigma phase, nitrides, and carbides with yield strengths well over 1200 MPa. Cryogenic fracture toughness testing at 77K was also conducted and K JIC values above 200 MPa.m 1/2 were observed. After the successful testing of the SPARC TFMC case, weld qualification was conducted for the SPARC TF coil. A semi-automated TIG welding process was developed that utilized ER316LMn filler wire and N enhancement in the shielding gas to achieve strengths and fracture toughness comparable to XM-19 base material. The data generated from the extensive TFMC studies, TF weld qualification, and challenges related to the forging size
and property coupling at 4K will be presented.
For superconducting magnets and other applications, enhancing the critical current density (Jc) is required. There are several possible approaches for enhancing Jc in REBa2Cu3Oy coated conductors (CCs); one is by introducing and tailoring pinning centers to immobilize vortices. Another is by enhancing the thermodynamic critical field (Hc∝(ξλ)-1) through reducing the penetration depth (λ) and the coherence length (ξ). Previously, we have shown a large enhancement in Jc at not only self-field but also in-field by introducing a high density of incoherent BaHfO3 nanoparticles (BHO NPs) of a tailored size into (Y0.77Gd0.23)Ba2Cu3Oyc ((Y,Gd)123) CCs, which leaves the matrix unaltered with just slightly decreased superconducting properties[1]. Reducing λ and ξ would improve Hc and consequently Jc. If both thermodynamic and pinning optimization routes can be combined, Jc can be dramatically improved.
In this work, we combined the thermodynamic route (decreasing λ and ξ by tuning the carrier density) with our previously developed methods to tailor the size and incorporate high densities of incoherent BHO NPs. We obtained Jc∼150 MA/cm2 at 4.2 K in self-field [2]. Moreover, the remarkably high pinning force in the nanocomposite (Y,Gd)123 CCs reached ~3.17 TN/m3 at 4.2 K and 18 T (H||c). Detailed microstructural and superconducting properties for nanocomposite RE123 CCs will be presented.
References
[1] M. Miura et al., NPG Asia Materials 9 (2017) e447.
[2] M. Miura et al., NPG Asia Materials 14 (2022) 85.
At liquid He temperatures and low magnetic fields, ReBCO films and coated conductors (CC) can have extremely large critical current densities ($J_c$), in excess to 100 MA/cm$^2$, the highest among known superconductors, making CCs very attractive for power applications. However, $J_c$ tends to decrease sharply as either $T$ or $H$ increases, thus additional pinning centers must be introduced to increase it to useful levels at technologically relevant $T-H$ conditions. Through the contributions of many research groups, a good understanding of the processing-properties correlations in CCs has been obtained, and a variety of routes to enhance vortex pinning has been developed. In this talk I will review the basics of the pinning properties associated to the different types of disorder and discuss some of our recent results as examples. By film growth conditions manipulation, addition of second phases, and thermal treatments, we can not only increase $J_c$ but also tune it for the requirements of specific applications. Our characterization toolkit includes imaging of defects and detailed $J_c(T,H,\Theta)$ measurements, with emphasis in the dependence of $J_c$ on the orientation of the magnetic field ($\Theta$). We also investigate the influence of the fast vortex dynamics that occurs because of the strong thermal fluctuations of vortices in HTS, which results in time decays of the supercurrents due to flux creep effects, and significant dissipation below $J_c$.
C-axis aligned BaZrO3 (BZO) nanorods formed via strain-mediated self-assembly in BZO-doped YaBa2Cu3O7-x (BZO/YBCO) nanocomposite films can provide strong pinning to the quantized magnetic vortices. While the strain initiated from the BZO/YBCO lattice mismatch plays a critical role in nucleation and evolution of the BZO nanorods, it also leads to a highly defective BZO/YBCO interface and hence reduced pinning efficiency of BZO nanorods. This work reports a recent study in probing the effect of BZO/YBCO interface on the pinning efficiency of the BZO nanorods as the interface is repaired dynamically during the BZO nanorod growth using Ca doping. Within the BZO doping range of 2-8 vol.%, significantly enhanced pinning efficiency of the BZO nanorods have been observed. A peak enhancement up to five-fold of critical current density at 9.0 T and 65-77 K has been obtained in the 6 vol.% BZO/YBCO nanocomposites after the interface repair. This result not only illustrates the critical importance of the BZO/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO nanorods.
Keywords: YBCO nanocomposite film, artificial pinning center, vortex pinning efficiency, coherent interface, dynamic lattice enlargement
Acknowledgements
This research was supported in part by NSF contracts Nos: NSF-DMR-1909292, the AFRL Aerospace Systems Directorate, the Air Force Office of Scientific Research (AFOSR), and the U.S. National Science Foundation DMR-2016453 for TEM characterization.
We present progress in development and understanding of the in-field performance of REBCO conductor with Artificial Pinning Centers (APCs) in the form of BMO nanorods (M = Zr, Hf, Sn, etc.). First, we present TEM findings on in-plane strain accommodation mechanisms between BMO and REBCO matrix, where the interfaces have been found to never be fully coherent, and that the degree of semi-coherency drives the equilibrium nanorod diameter, which is found to assume discrete values. Second, we present findings on the in-field performance as a function of operating field and temperature (B, T) and the degree of correlation between different operating regimes. We address the high level of statistical fluctuations of in-field performance found in both production and research conductors and analyze the features behind pairs of Jc(B1, T1) and Jc(B2,T2) that show high level of correlation. Third, we present results on the feasibility of using indirect, non-destructive characterization methods to predict Jc(B, T) performance over a wide range of fields and temperatures, as high temperature performance (65-77 K) is found to be poorly correlated to low-temperature (4.2 – 40 K), intermediate-to-high field (~3-30 T) performance of interest for applications. We present an in-depth study of scanning Raman spectroscopy and 2D-XRD features and their effect on the resulting in-field performance over 4.2-77 K and measured fields of 0-14 T. The main identified features that correlate to in-field performance are analyzed both in terms of level of correlation and in terms of the underlying microstructural features.
This work was funded by award DE-SC0016220 from the U.S. Department of Energy, Office of Science – High Energy Physics and award DE-AR0001374 from Advanced Research Projects Agency – Energy.
The spin-momentum locking of surface states in topological materials can produce a resistance that scales linearly with magnetic and electric fields. Such a bilinear magneto-electric resistance (BMER) effect offers a new approach for information reading and field sensing applications, but the effects demonstrated so far are too weak or for low temperatures. This talk reports the first observation of BMER effects in topological Dirac semimetals; the BMER responses were measured at room temperature and were substantially stronger than those reported previously [1]. The experiments used topological Dirac semimetal alpha-Sn thin films grown on silicon substrates. The films showed BMER responses that are one million times larger than previously measured at room temperature and are also larger than those previously obtained at low temperatures. These results represent a major advance toward realistic BMER applications. Significantly, the data also yield the first characterization of three-dimensional Fermi-level spin texture of topological surface states in alpha-Sn.
Reference:
[1] Science Advances 8, eabo0052 (2022). DOI: 10.1126/sciadv.abo0052
Topological materials have signature electronic states with high intrinsic mobility due to their symmetry-protected quantum channels. The large spin orbit coupling in narrow bandgap alpha-Sn provides a fruitful playground for basic research in topological electronics through exploration of its various electronic dimensionalities including 3D topological insulator and Dirac semimetal phases. Overcoming fabrication challenges associated with the low temperature phase of tin, we present a comprehensive union of experimental and theoretical descriptions of the magnetoelectric transport in this material and its band structure [2]. We address various complexities that showcase the rich physics present in gray tin and in topological insulators and Dirac semimetals in general [3]. In addition, we explore topological heterostructures with magnetic materials in order to interact directly with the unique spin textures present in topological materials. Thin film parameters such as strain, interface sharpness, thickness, and doping profiles play vital roles in determining the resulting electronic behavior of these materials. Magnetotransport measurements provide evidence to support our theoretical model using magnetic and electric fields at varying temperatures and geometries as experimental knobs. We reveal quantum oscillations, charge neutrality point behavior, and various Hall effects that paint a picture of the diverse and elegant transport physics in gray tin and topological heterostructures.
The DOE Hydrogen and Fuel Cell Technologies Office (HFTO) carries out applied research, development, and demonstration (RD&D) of hydrogen and fuel cell technologies across multiple sectors enabling innovation, a strong domestic economy, and a clean, equitable energy future. Hydrogen presents promising decarbonization opportunities for transportation, energy storage, and large-scale industrial and chemical processes. Many larger-scale end uses will require the high energy density that liquid hydrogen offers, but the cryogenic conditions required for its delivery and storage present a number of challenges. HFTO is actively pursuing a number of RD&D efforts on liquid hydrogen infrastructure components and technologies to reduce cost and lower barriers to the increased commercialization of hydrogen technologies across several sectors. This presentation will provide an overview of HFTO’s priorities and activities on liquid hydrogen.
Hydrogen is often cited as a potential fuel alternative to enable carbon reduction in hard to abate sectors, such as in aviation propulsion. However, hydrogen’s low volumetric energy density while in gaseous form makes it impractical for many transport applications. To overcome this challenge, storage in a liquid form has been identified as a potential solution to unlock carbon-free hydrogen as a viable fuel source. While there has been significant funding and research to significantly reduce the cost of hydrogen to less than one to two dollars per kilogram, this work frequently does not address detailed adoption characteristics and total switching costs related to end-use markets. In the recently released report from the U.S. Department of Energy, “Pathways to Commercial Liftoff: Clean Hydrogen,” it is acknowledged that “…hydrogen powered flight for long-haul aviation…may remain decades away….” highlighting the need for significant infrastructure development and the turnover of the existing aircraft fleet.
To address these end use market adoption hurdles, a variety of market adoption characteristics must be considered and addressed. This presentation will discuss a framework for assessing commercial adoption factors for cryogenic hydrogen applications and identify some key risk factors for future consideration of technologists and commercial practitioners as these technologies are moved to market.
Cryomech has developed a small capacity, low vibration helium reliquefier for use with commercial NMR cryostats. NMR systems are highly sensitive to vibration and thus utilize liquid helium to cool the magnet. Due to the helium shortage and rising cost of helium, many small labs cannot operate their NMR systems. Large facilities with multiple NMR systems can utilize a large-scale liquid helium plant and helium recovery system eliminate helium loss. However, this is not cost effective for smaller university labs with only one or two cryostats. The reliquefier discussed here is based on Cryomech’s existing reliquefier design and uses a PT405-RM pulse tube cryocooler. The system can liquefy 1.44 L/day from room temperature helium and 4.2 L/day from liquid helium boil-off with 5 kW of input power. To operate with the highly sensitive NMR systems, the design had to be modified to isolate the vibration from the pulse tube cryocooler from the cryostat. Through implementing various isolation methods, the dominant frequencies from the pulse tube were reduced by an order of magnitude. In this paper, we discuss the design of the reliquefier, the results of the thermal and vibration tests, and compare scan images from a commercial NMR cryostat with the helium reliquefier installed.
Quantum detection of single photon achieves its highest sensitivity for temperatures below 2 K. The cooling requirements for such applications are very low, a few milliwatts for current harness heat intercept and radiation shielding. For that purpose, we are developing a compact cryocooler based on a 4He JT cooler. A Stirling-type pulse tube will provide the pre-cooling of two intermediate stages of the JT. The pulse tube is the key component for miniaturization and energy consumption. With low cooling power goals, a miniaturization work has been done on the pulse tube with the aim of reducing the size and power of compressor units.
The pulse tube configuration is using two units, connected together by a heat intercept providing pre-cooling for the lowest temperature stage. Cooling power at cold tip as well as intercept cooling power have been measured. Swept volume of the low temperature unit compressor and pressure waves at different spots are also measured. The simulation software Sage has been used in parallel to study the impact of the size of the pulsation tube on the pulse tube performances.
Three cold units pulse tubes have been tested in similar conditions. Net cooling power, power at the intercept and impact of the tube size on performances will be discussed.
CMB-S4 is a ground-based experiment that will use large-format bolometer arrays to map Cosmic Microwave Background (CMB) polarization with unprecedented sensitivity, including the search for a B-mode polarization pattern associated with cosmic inflation. The focal planes on which the superconducting detectors are mounted each weigh about 20 kg and must be cooled at 100 mK. To reach this temperature for a first receiver fielding prototype hardware, we have developed an Adiabatic Demagnetization Refrigerator (ADR) used in conjunction with an existing 4He/3He sorption refrigerator.
The ADR unit described here is based on a CPA pill (crystal alum, CrK(SO4)2 12 H2O). It is backed by a 3-stage (4He/3He/3He) sorption fridge, coupled through a 3He gas-gap heat switch. This heat switch is connected to a 3He stage of the sorption fridge to dissipate the heat generated by magnetization. The ADR is cycled with a 1.5 T magnetic field. The residual field at the location of the detectors is kept below 50 µT thanks to a ferromagnetic magnetic shield. The pill is supported by Kevlar lines, which are doubly intercepted by the 4He and 3He stages of the sorption fridge in order to reduce conductive heat losses. In these conditions, the ADR provides 2 µW of cooling power during 48 hours at 100 mK. This ADR has been designed by CEA/DSBT in France and is now implemented in a cryostat at Caltech.
ABSTRACT:Small-scale helium liquefiers with typical liquid-helium production of the order of tens of liters per day are required for cryogenic applications, such as cryogenic research experiments and operation of superconducting magnets in hospitals. These liquefiers are typically based on 4 K regenerative cryocoolers, including Gifford-McMahon (GM) or pulse-tube (PT) cryocooler. However, due to the heat exchange between the helium being liquefied and the outer wall surface of the cylinder, the precooling process is inefficient, leading to a superheat of helium at the cold head and a low liquefaction rate. To address this challenge, this study proposes a gas-coupled GM/Joule-Thomson (JT) hybrid helium liquefaction system. The system uses the internal helium of the GM cryocooler as the source for JT throttling and liquefaction, resulting in highly efficient precooling and liquefaction. There are different effects of direct current gas flow (DC flow) mass, temperature and pressure on the performance of GM cryocooler and JT stage of the system, which should be comprehensively considered. To determine the impact of interstage pressure, first and second stage precooling temperature, hot end DC flow ratio and recuperator effectiveness on the liquefaction rate, a Pressure-Enthalpy map analysis and thermodynamic calculations were performed. For a GM cryocooler with 1 W cooling capacity at 4.2 K, and a charge pressure of 1.6 MPa, and a secondary cold end temperature of 5 K, it was found that inducing a DC flow rate of only 50 mg/s at the cold end is sufficient to achieve the ideal helium liquefaction rate, corresponding to a sufficiently precooled helium gas, which is not achievable with conventional small-scale helium liquefiers. This DC flow is less than 1% of the actual flow amplitude of the cryocooler, and its effect on the performance of the cryocooler can be deemed negligible. The new helium liquefaction method proposed in this study has the potential to increase the liquefaction rate of existing small-scale helium liquefiers.
Adsorption refrigeration is a significant method for achieving temperatures below 1 K. The process involves pumping a helium tank to a high vacuum by adsorbents, resulting in the liquid helium reaching sub-Kelvin temperatures. The adsorbents are then heated to desorb 4He, which condenses in the region below the critical temperature, and the adsorption refrigeration cycle is repeated. This paper presents the design and experiments of a 4He sub-Kelvin adsorption cooler that can achieve an ultra-temperature of 773 mK, continuously refrigerate for 9.4 hours without any additional heat power, and has a cooling power of 100 μW at 803 mK.
A high power density induction electromotor operating in the temperature range of 113 K – 120 K and utilizing the cryo-cooling capacity of bio-LNG fuel for thermal management is under development. Incorporating high current density Al conductor operating up to 120 K reduces its electrical resistance to 1/3 of room temperature and thereby increasing the motor’s power density. In this paper we present FEM modeling of cooling effects of a turbulent 2-phase flowing liquid natural gas on the motor stators’ coils. We modelled effects of various flow rates per slot combined with various energy loss levels on maximum temperature of the stator coils and fluids. Effects of number of cooling channels per slot have also been modelled. Typically maximum temperatures in the coils were around 140 K.
Electrification has been proposed as a route to decarbonizing air travel. Conventional electric motors are too heavy to achieve the power densities required for aviation so superconducting motors for aircraft are being developed. Superconductors, however, work at cryogenic temperatures, which indispensably require a reliable and efficient cooling mechanism with a cryocooler. The successful application of superconducting technology critically relies on a proper cryogenic cooling system. The Robinson Research Institute is developing a 3 MW superconducting motor using an HTS HTS (High Temperature Superconductor) rotor operating at 50 K and MgB2 running at near 20 K for the stator. The motor is intended to run at a shaft speed of 4500-6000 rpm to directly drive a ducted fan. A key challenge is the removal of heat from a cryogenic spinning rotor to a stationary refrigerator so it can be rejected at ambient temperatures. Previous motors have utilized pumped or thermosyphoned cryogens. Transferring a cryogen to a spinning rotor requires rotary seals, usually ferro-fluidic seals. The aircraft application demands a compact and low weight solution. Moreover, ferrofluidic seals are not compact and generate significant amounts of heat at high shaft speeds, needing additional cooling and thermal isolation from the cryogenic environment. This paper presents the design, modelling and testing of a concept for coupling a stationary cryocooler to a superconducting rotor in an efficient manner without ferrofluidic seals to allow compact cooling with no cryogen transfer.
Storage of liquid hydrogen at low pressures and temperatures is advantageous in terms of overall system weight compared to high-pressure gas storage at room temperature. The weight penalty for insulation of cryogenic media is typically outperforming the combined weight and volume penalty of high-pressure storage. For aviation applications, where light-weight and compact design is key, it is, therefore, preferred to store the propellant as liquid. In the context of hydrogen, this implies storage of the liquid between 20K and 30K, depending on tank pressure. As the fuel cell, which converts chemical energy to electrical energy, requires the hydrogen to be provided at temperatures well above the freezing level of water, hydrogen extracted from the tank must to be thermally conditioned, to comply with applicable requirements.
In the presented work, a liquid hydrogen and fuel cell based electrical propulsion system for aircraft is developed, which incorporates several novel technologies and non-trivial operating conditions. One major focus is the utilization of additive manufacturing enabling advanced geometric designs to enhance performance and reduce weight. However, the influence of hydrogen and cryogenic operating conditions on thermal and mechanical properties of additively manufactured materials must be assessed and accounted for in the design process.
The underlying architecture of the investigated hydrogen-electric aircraft powertrain incorporates several heat exchangers with different purposes. One of the heat exchangers is tasked with transfer of heat from a liquid coolant cycle to the gaseous hydrogen in order to rise its temperature to the working level of the fuel cell (>300K). The design of the heat exchanger is based on empirical formulae for cylindrical tube bundles (pins), which enhance heat transfer on the gas side. Alternating flow planes of gaseous hydrogen and liquid coolant media are stacked to reach a number of units, which generate the desired heat transfer rates and keep the pressure loss due to friction below the defined limit. The particular arrangement of rows, columns, pin diameter or distances between individual pins is optimized to arrive at the minimum structural mass, while satisfying heat transfer and pressure drop requirements. Boundaries for this parameter optimization may originate from manufacturing limitations, like the minimum thickness of fine structures impacting the reliability of the manufacturing process. Therefore, accompanying manufacturing tests are required, to feed the optimizer with meaningful limits.
After the initial optimization, computational fluid dynamics (CFD) analysis confirms the performance of the entire heat exchanger, including the intake and outflow manifold. Lastly, the lower limits of wall thicknesses may be defined by either the manufacturability in the 3d-printer or the differential pressure across the wall causing material stress. Therefore, mechanical analysis is performed, to confirm that the manufacturing limit is the actual driving limit for the minimum wall thickness.
Comparison of results of the analytical method with CFD show very good agreement with deviations of average media temperature at the heat exchanger exit of less than 3% for relevant conditions. The pressure drop results deviate predictably in the order of 50%, which can be accounted for with a correction factor. CFD analysis of the entire heat exchanger shows good agreement of the flow properties in the heat exchanger core, but also demonstrate that the intake (from pipe flow into heat exchanger core) and outflow plena can contribute significantly to the overall pressure drop, depending on flow conditions and geometry.
This presentation summarizes the entire development process of a heat exchanger starting with the requirements derivation based on a system analysis, via the initial design optimization based on empirical coupled thermal and fluid mechanical formulae to CFD and mechanical strength analysis of the detailed design. Close attention is paid on the additional degrees of freedom and restrictions in design gained by additive manufacturing as well as the impact of the manufacturing method on material properties especially in the context of cryogenic hydrogen.
Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904B.
To enable the design of future in-space cryogenic propellant vehicles such as Lunar and Martian ascent and descent stages and the nuclear thermal propulsion system, high accuracy models of various phases of the propellant transfer process are required. This paper focuses on modeling of steady state flow through the transfer line that connects a propellant tank to an engine or customer receiver tank, which is required to set limits on the allowable heat flux into the line. Using the largest ever collection of available cryogenic heated tube data, universal cryogenic flow boiling correlations were recently developed for various regimes of the boiling curve. However, to model flow boiling in heated tubes, these individual correlations must be patched together to provide a continuous predictive curve of wall superheat as a function of preponderant parameters. This presentation provides an overview of the individual flow boiling correlations along with the logic and methodology for patching the correlations together to produce a single continuous boiling curve. Resulting flow boiling curves are presented for a variety of flow conditions for illustration.
In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems.
Author: Erin Tesny
Co-authors: Jason Hartwig, Vishwanath Ganesan, Issam Mudawar, Mariano Mercado
Understanding two-phase cryogenic propellant behavior is key to enabling technologies for future spaceflight missions to the Moon and Mars. Developing accurate models of two-phase flow phenomena, particularly flow boiling in the heating case is relevant to the propellant transfer process both in microgravity and on other planetary surfaces. Currently there are no model-verified universal correlations for the heat transfer coefficient across the boiling curve for cryogens. Previous work has focused on developing these universal correlations for cryogens in a heated tube for various regimes across the boiling curve. This work demonstrates how these correlations have been ported into Thermal Desktop. This Thermal Desktop model has then been used to model a historical dataset of flow boiling experiments in the heating configuration for Helium. The new correlations show an improvement over the original built-in flow boiling correlations in Thermal Desktop in predicting the experimental results when compared to the original dataset.
An instrument based on a modification to the 3-omega thermal conductivity technique that allows precise measurement of thermal properties in fluids is presented. Existing hot-wire techniques have difficulty measuring thermal conductivity because of the effects of natural convection. This device's geometry restricts fluid motion to enable a direct high-precision measurement of a fluid's thermal conductivity. In addition, this device can also measure the specific heat of the fluid. The device is described and initial measurements from low temperature to room temperature and a range of pressures for several fluids are discussed.
Available experimental data dealing with critical heat flux (CHF) of liquid hydrogen (LH2), liquid methane (LCH4), and liquid oxygen (LO2) in pool and flow boiling are compiled. The compiled data are compared with widely used correlations.
Experimental pool boiling CHF data for the aforementioned cryogens are scarce. Based on only 25 data points found in five independent sources, the correlation of Sun and Lienhard (1970) is recommended for predicting the pool CHF of LH2. Only two experiments with useful CHF data for the pool boiling of LCH4 could be found. Four different correlations including the correlation of Lurie and Noyes (1964) can predict the pool boiling CHF of LCH4 within a factor of two for more than 70% of the data. Furthermore, based on the 19 data points taken from only two available sources, the correlation of Sun and Lienhard (1970) is recommended for the prediction of pool CHF of LO2.
Flow boiling CHF data for LH2 could be found in seven experimental studies, five of them from the same source. Based on the 91 data points, it is suggested that the correlation of Katto and Ohno (1984) be used to predict the flow CHF of LH2. No useful data could be found for flow boiling CHF of LCH4 or LO2. The available databases for flow boiling of LCH4 and LO2 are generally deficient in all boiling regimes. This deficiency is particularly serious with respect to flow boiling.
The past 20 years have seen great advances of pulse tube coolers. Behind these are the deeper and clearer understanding of their working principles and more accurate simulation aided by more powerful computing capability. This paper mainly generalizes the author’s understandings of the system, especially from the aspects of thermodynamics, acoustics and fluid dynamics. Maybe the most intriguing part is thermodynamics. The essential difference with ordinary steady flow system is that there is no gas portion that goes through all the components in a pulse tube cooler and there is no single P-V or T-S diagram that can cover all the thermodynamic cycles inside the system. This feature actually brings fundamental changes in understanding how the system operate, which overturns previous classical understanding of the Stirling coolers. Meanwhile, the same oscillating nature of the flow inside the pulse tube cooler easily lends to the use of acoustic theory to interpret the dynamics inside the cooler and leads to a more efficient design methodology as well as more innovations. As the final part, our most recent work, which, a little bit ironically, shows that in the porous regenerator, one may not need to think about the change brought about due to this oscillating nature when considering the flow resistance coefficient.
Cryopreservation has emerged as a promising technology to provide the semipermanent storage of biomaterials widely used in assisted reproduction and cell therapy. A large portion of successful cryopreservation requires the combination of ultra-rapid cooling and appropriate low-toxicity cryoprotectant agents, which inhibits the formation of ice crystals that damages the cells lethally. Conventional approaches are not competent in realizing high enough cooling rate and large enough volume of the samples, and more importantly, not able to track the instant appearance of the sample at a microscale level during the momentary cooling process. A rapid freezing device for the droplet sample study purpose was designed and developed, which is capable of microscopic visualization of sample on a sapphire surface at a vitrification cooling rate up to 10^4 K/min. Cooling and freezing tests of several frequently used cryopreservation samples have been conducted on the device. The relationship between the crystallinity, the temperature uniformity and the cooling rate was interpreted, which provides new insights to a better understanding of the cryopreservation technology and guidance for new cryogenic bioinstrumentation development.
In this study, we present the understanding of magnetic stress in REBCO (Rare Earth Barium Copper Oxide) magnets, based on experimental results from a 26.4 T magnet [1] and a 45.5 T magnet [2]. Magnetic stress in a high-field magnet is a critical factor that can affect their overall performance and reliability. We address three approaches for developing an understanding of magnetic stress in high-field REBCO magnets. The first approach is based on the continuum mechanics, has been conventionally used for wet-wound magnets (e.g. epoxy impregnated magnet), mostly LTS(low temperature superconductor) magnets. The second approach is the contact mechanics, which was proposed to explain mechanical behavior of 26.4 T all REBCO no-insulation magnet. This approach enables considering both turn-to-turn separation and contact of dry wound magnets. Lastly, we are considering how to affect the screening current in REBCO magnet to the magnetic stress based on the results of the 45.5 T magnet, as known as screening current induced stress (SCS). Furthermore, we discuss the implications of our findings for the development of next-generation REBCO magnets for various high-field applications.
[1] Yoon, Sangwon, et al. "26 T 35 mm all-GdBa2Cu3O7–x multi-width no-insulation superconducting magnet." Superconductor Science and Technology, 29.4 (2016): 04LT04.
[2] Hahn, Seungyong, et al. "45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet." Nature, 570.7762 (2019): 496-499.
Since 2G HTS tapes have excellent features such as high in-field critical current (Ic) and tensile strength, they are suitable for various applications including high-field magnets. Fujikura Ltd. has developed high-performance 2G HTS tapes using IBAD and PLD techniques, and has supplied to many customers for years. In particular, the hot-wall PLD system that we have developed enables highly homogeneous Ic properties of the HTS tapes due to its very stable heating method. Also, we have succeeded in improving the in-field Ic by introducing artificial pinning centers to the superconducting layer.
In parallel with the development of the tapes, we have been evaluating various properties of the tapes and feeding them back into the manufacturing process. Especially, mechanical strength is an important factor, since it is often critical in high field magnet applications. Thus, we have focused on the evaluation of mechanical properties as well as (in-field) Ic evaluation. In magnet applications, the 2G HTS tapes are exposed to various electromagnetic and thermal stresses. Therefore, we have evaluated various strength parameters such as bending, compression, fatigue, and delamination, etc. in addition to tensile strength. Then we have worked to improve the strengths including introduction of a laser slitting technique.
In this presentation, the results of various characterizations we have performed are introduced.
Ultrahigh field high-temperature superconducting (HTS) magnets beyond 20 T have been developed worldwide. Rare-earth barium copper oxide (REBCO) coils are promising in terms of their high-field specifications as insert coils. However, mechanical damages of REBCO tapes are getting critical in spite of high stiffness of Hastelloy substrates. Plastic deformations have been frequently observed after ultrahigh field generation, nevertheless simulated stresses are lower than yield stresses of Hastelloy substrates.
It was pointed out that screening currents enhanced stresses of insert REBCO coils inside high fields generated by outsert coils. Some simulation results showed higher stresses than expected. In recent years, a REBCO tape rotation effect was proposed, and simulated screening current induced fields agreed with measurements. Hence, it was confirmed that the screening currents largely affected the coil deformations. In addition, it was reported that the coil deformations also affected the electromagnetic phenomenon due to the change of the self-/mutual inductances. The screening currents and the coil deformations influence each other, and excessive stresses due to screening currents damages insert REBCO coils.
In the presentation, we will show the screening current simulation results considering the REBCO tape rotation effect and the inductance change effect. We will also discuss the stress of REBCO coils. In addition, the azimuthal deformation of no-insulation (NI) REBCO tapes is simulated considering the individual turn movement. It reduces the hoop stress of NI REBCO coils.
Acknowledgement: This work was supported by the JSPS KAKENI under Grant 20H02125.
The heterogeneous nature of REBCO Coated Conductor (CC) properties poses significant challenges in the fabrication of high magnetic field devices. Our goal is to peer below the cartoon representations of CC so that, amongst other things, we might better understand whether a CC from one manufacturer is interchangeable with that from another. This involves knowledge of a broad range of electromagnetic, geometric, microstructural, and Jc(θ,B,T) properties, and their variations that collectively pose challenges for the fault tolerance of REBCO CC devices. Accordingly, comparative measurements of critical current, critical temperature, flux penetration, tape geometry, and extensive microscopy were performed on recently purchased samples from multiple manufacturers. Our analyses reveal many deviations or absences from manufacturers’ specifications, while a comparison of mechanically and laser slit tape shows a diverse array of slitting characteristics amongst the manufacturers and variation in properties along the length of a single tape and between those made to the same specification. Overall, the aim of this study is to flesh out appropriate ways to understand the real conductor below the manufacturers’ cartoons so as to avoid surprises in our REBCO CC coil development program.
Planar Josephson junction (JJs) provide an attractive platform to realize topological superconductivity and implement fault-tolerant quantum computing [1,2]. By embedding two gate-tunable Al/InAs JJs in a loop geometry, we measure a π jump in the junction phase with an increasing in-plane magnetic field [3]. This jump is accompanied by a minimum of the critical current, indicating a closing and reopening of the superconducting gap, strongly anisotropic with in-plane field [3]. Our theory confirms that these signatures of a topological transition are compatible with the emergence of Majorana bound states (MBS). While the key element for the fault-tolerant quantum computing is the non-Abelian statistics of MBS, its demonstration is conspicuously missing. By extending our work [3], we propose how to demonstrate the non-Abelian statistics through MBS fusion in mini-gate controlled JJs [1]. Surprisingly, we show that with a gate-tunable spin-orbit coupling (SOC), the same planar JJs, sought after for topological superconductivity, could also support a much broader range of applications. The time-dependent SOC offers unexplored mechanisms for switching JJs, accompanied by the 2π-phase jumps and the voltage pulses corresponding to the single-flux-quantum transitions, key to high-speed and low-power superconducting electronics. In a constant applied magnetic field, with SOC, anharmonic current-phase relations, calculated microscopically in these JJs, yield a nonreciprocal transport and superconducting diode effect [4-6]. Together with the time-dependent SOC, this allows us to identify a switching mechanism at no applied current bias and supporting fractional-flux-quantum superconducting circuits [6].
[1] T. Zhou, M. C. Dartiailh, K. Sardashti, J. E. Han, A. Matos-Abiague, J. Shabani, and I. Zutic, Nat. Commun. 13, 1738 (2022).
[2] T. Zhou, M. C. Dartiailh, W. Mayer, J. E. Han, A. Matos-Abiague, J. Shabani, and I. Zutic, Phys. Rev. Lett. 124, 137001 (2020)
[3] M. C. Dartiailh,W. Mayer, J. Yuan, K. S. Wickramasinghe, A. Matos-Abiague, I. Zutic, and J. Shabani, Phys. Rev. Lett. 126, 036802 (2021).
[4] M. Amundsen, J. Linder, J. W. A. Robinson, I. Zutic, and N. Banerjee, arXiv:2210.03549, under review in Rev. Mod. Phys.
[5] D. Monroe, M. Alidoust, and I. Zutic, Phys. Rev. Applied 18, L031001 (2022),
[6] D. Monroe, D. Tringali, M. Alidoust, and I. Zutic, preprint.
In general, the critical current (Ic) in a conventional Josephson junction (JJ) is independent of the current sweeping directions, when either time reversal symmetry (TRS) or inversion symmetry is presented. However, when both symmetries are broken, Ic can display different values, thus the Josephson diode effect (JDE), depending on the direction of current being swept. Like the diode effect in p-n junctions for microelectronics, JDE is expected to find important applications such as passive on-chip gyrators, radio-frequency circulators, etc.
Non-centrosymmetric superconducting systems are usually utilized to break inversion symmetry. TRS, however, is hard to break, and magnetic JJs or finite magnetic fields are generally needed. In this regard, it is surprising that in recent experiments magnetic-field free JDE was observed in non-magnetic materials, thus calling for more investigations. In this talk, I will present our recent progress in exploring magnetic-field free JDE in asymmetric superconducting quantum interference devices (SQUIDs) in Dirac semimetals. We will show that the coupling of the superconducting phases between the surface and bulk states in Dirac semimetal SQUIDs can lead to TRS broken and enable a zero-magnetic-field JDE.
The magnetic and dielectric/ferroelectric properties couple to each other in magnetolectric materials. The magnetic field can influence and manipulate the electric polarization and/or the electric field influences and manipulates the magnetization in a material. ME is attractive from an applications perspective in insulating materials because large power dissipation due to electric currents is eliminated. Other potential applications include magnetic sensors, data storage , electric control of magnetic qubits and more. Usually, ME coupling is studied in inorganic oxides where spin orientations form ordered patterns – (anti)ferromagnets. Here, our results demonstrate ME coupling in molecule-based complexes that demonstrate a bistable spin state resulting from a change in the d orbital occupancy. This phenomenon, Spin State Crossovers (SSCs), can produce substantial changes in the crystal structure, lattice parameters, dielectric, optical, and mechanical properties of the material and are often sharp and hysteretic. We demonstrate that in a Mn(III) based complex, an applied magnetic field induces a spin state switching accompanied by a change in electric polarization due to symmetry breaking phase transition. I will follow this with more examples of magnetoelectric coupling at lower fields.
Spin crossover complexes are a large class of materials where the magnetic-field-induced switching can modify the structure and here we show that this is a route to ME coupling. The interplay of spin, charge, and lattice needed to create such magnetoelectric coupling is an intriguing challenge and a source of new discoveries.
Cryogenics will play a critical role in achieving net-zero emissions targets. Cryogenics can contribute to reducing emissions through various technologies including the development of cryogenic energy storage systems using low-temperature liquids such as liquid nitrogen, to store excess renewable energy generated during times of low demand. The stored energy can be used during times of high demand, reducing the need for fossil fuel power generation, and increasing the use of renewable energy.
Cryogenic technologies can also be used in industrial processes to reduce emissions. For example, the use of cryogenic cooling during the manufacturing process can reduce the energy required to produce products and can reduce emissions from manufacturing processes.
Liquid hydrogen is emerging as a principal player in managing the reduction of carbon emissions from transport and electrification but also enabling superconducting applications operating at 20 kelvins for diverse applications.
Achieving net-zero emissions will require a combination of strategies, including renewable energy development, superconducting applications, energy efficiency improvements. There are many initiatives on the use of cryogenics for the cleaner economy. This presentation will provide an overview on the role of cryogenics in addressing net zero emission targets.
The Ministry of Business Innovation and Employment (the Ministry) is one of the largest government departments in New Zealand. It is the lead agency for the regulatory systems for Energy and Resource Markets which include the electricity system, gas system, fuel system and petroleum and minerals. It also has teams dedicated to innovation from both a policy and technology standpoint in its Science, Innovation and International branch.
In May 2022 the New Zealand Government launched its first Emissions Reduction Plan, which outlined a number of actions to progress the country towards a more resilient, low emissions economy. As part of this plan the government has committed to develop a hydrogen roadmap to set Government objectives for hydrogen, and its potential to reduce emissions and maximise economic benefits for New Zealand. New Zealand’s Climate Change Commission identified innovation and system transformation as one of three pillars for a comprehensive policy package to reduce New Zealand’s emissions.
Another action in the Emissions Reduction Plan is Sustainable Aviation Aotearoa (SAA), which was launched in November 2022 by the Ministry of Transport. SAA is a public- private leadership body to guide the decarbonisation of the aviation sector, including through operational efficiencies, infrastructure improvements, and frameworks to encourage research, development and innovation in sustainable aviation.
SAA has established three working groups to explore zero emissions aircraft, sustainable aviation fuel and strategic settings to enable these. At the same time Air New Zealand, New Zealand’s national airline carrier, announced its Mission Next Generation Aircraft accelerator programme. The programme has an ambitious goal for a commercial demonstrator zero emissions aircraft flight in 2026. Ultimately, they are preparing to replace their Q300 domestic fleet with aircraft likely to be powered by green hydrogen or battery hybrid systems from 2030.
The Ministry’s Innovative Partnerships team, alongside colleagues in the Energy Markets and Resources team will present on our Government’s initiatives in hydrogen, sustainable aviation fuels and advanced aviation in New Zealand. It is exciting to see an emerging eco-system to enable cutting edge technologies in cryogenics, hydrogen fuel cells and hybrid-electric aircraft to be trialed and tested in Aotearoa New Zealand.
In this presentation we point out where are the opportunities for cryofuels (LH2 and LNG) and impact on our superconducting industry applications, primarily wind turbine generators and electric aircraft. We will point out the opportunities for growing the hydrogen economy, reducing CO2 emissions and thus help to reduce global warming. Our discussion will focus on the potential of superconducting wind turbine generators to lower the LCOE (electricity) and the potential to help enable low-cost gaseous hydrogen, and liquid hydrogen. This same low-cost electricity from wind energy ( and other sources) is what can also enable the low-cost compression and liquification of hydrogen for transportation.
There is the potential use of cyrofuels (LH2 and LNG) for electric aircraft. Besides using the cryofuel to burn in turbines to reduce emissions, there is also the potential to use the cryofuels for thermal management within the aircraft. Using the cryofuels for thermal management can potentially enable the increase in power density for the drivetrain components such as generators, cables, and motors. We will discuss the potential of increased power density and efficiency by using the cryofuels for thermal management of hybrid electric aircraft.
For both wind turbine generators and rotating equipment for electric aircraft (motors and generators) the technical drive has been to use rare earth permanent magnets. The present prediction is for shortages and rising prices for rare earth permanent magnetic materials between now and 2035, if we are going to implement all the wind energy and E-transportation desired. The issue is can superconducting offer a better price/performance than using rare earth permanent magnets. We ask the question? Can superconductivity play a greater role to enable and reduce the cost of offshore wind energy, and enable better price/performance drive trains for electric aircraft.
One of the reasons gaseous fuels, methane, and hydrogen, are renewable, sustainable replacements for traditional liquid hydrocarbon-based transportation fuels is their small carbon footprint. Global awareness of the immediate need to address impacts of emissions from transportation energy use has emphasized urgency of changes from business as usual. However, the transition from existing fuels to new fuels is complex because their usage is huge, and so many variables influence the rate of adoption. One only need to read credible energy outlooks of major energy companies and international or national energy agencies along with studies of the water, energy, food nexus to appreciate these complexities. Marchetti’s insightful numerical modeling of the rate of transition among different energy sources over the past two centuries with credible recorded usage data shows the time scale for appreciable change is several decades. A further important observation of this work is that transitions among energy sources were and are driven by substitution of superior technology rather than by depletion of prevalent sources. These observations incentivize developments of multiple more efficient, less expensive, robust, scalable methods of production, liquefaction, storage, transport, delivery, and dispensing of hydrogen and natural gas are essential to accelerate adoption by transportation customers. This paper focuses on a few examples of how process intensification in advanced liquefiers for LNG and LH2 at the same location could reduce capital costs, energy costs, and foot prints of different sized liquefiers. These solutions help address gaps in existing technology for several essential needs such as refueling station or bunkering-sized liquefiers, boil-off management systems on several scales, or modular containerized, several tonne/day liquefiers that can be scaled by numbers to make distributed-sized industrial plants that match localized fuel demands from mobile users
The European X-Ray Free Electron laser (XFEL) has successfully been operated for more than 5 years. The superconducting cavities and magnets being key components of the cryomodules constituting the XFEL linac and injector are operated at 2 K in a liquid helium bath. A four stages cold compressor system is used to return the vapor to the XFEL helium refrigerator with the capability of pumping up to 110 g/s for compensating static and dynamic heat losses at 2 K.
In this paper technical challenges with regard to the cold compressor system as availability, 2K pressure stability and contamination of the 2K circuit are summarized. Influence of hydrostatic head on operation of all cooling circuits is analyzed. Issues related to the use of some kinds of instrumentation as pressure transmitters, flow meters and level sensors are discussed. The experiment regarding the future XFEL project as doubling of safety valves is described.
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) operates the Cryogenic Moderator System (CMS) which provides hydrogen cooling at 20K to three neutron moderators. Each hydrogen circuit is protected by multiple burst discs and reclosing relief valves. As a result of the Proton Power Upgrade (PPU) project, the CMS moderator circuits will hold more hydrogen and thus require piping modifications. The design of a new hydrogen relief system and compliance with the national electrical code (NEC) will be discussed. Operational experience has demonstrated that transient pressure increases in these hydrogen loops often result in rupture of the burst discs. The causes for pressure transients in the system that might lead to hydrogen venting are varied and complex, for example loss of vacuum or cooling. Dynamic simulation and analysis of the parameters considered as the worst-case relief venting scenario were performed and will be presented.
The Proton Improvement Plan-II (PIP-II) is a superconducting linear accelerator being built at Fermilab that will provide 800 MeV proton beam for neutrino production. The linac consists of a total of twenty three cryomodules of five different types. Cooling is required at 2 K, 5 K and 40 K. The Cryogenic Distribution System (CDS) consists of a Distribution Valve Box, ~285 m of cryogenic transfer line, modular Bayonet Cans to interface with cryomodules, and a Turnaround Can. The cryogenic system must provide protection from over-pressure by sizing pressure relief devices for all volumes and process line circuits. The cryomodule cavities have dual pressure ratings, 4.1 bara when cold and 2.05 bara when warm (T>80K) that impose unique challenges on the relief system. A relief system has been designed to meet these challenges in addition to satisfying functional requirements such as prohibition of venting relieved helium in the linac tunnel. This paper will provide a detailed description of the PIP-II CDS Pressure Safety system including the key relieving cases, methods for determining heat flux during a loss of vacuum, relief piping layout, and the selection of relief devices. Furthermore, vacuum vessel relief sizing to protect the CDS vacuum shells from over pressure during an internal line rupture will be presented.
This abstract has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Safe, compact, lightweight, economical and efficient hydrogen storage technology is the key to the comprehensive development of hydrogen economy. Compared with other hydrogen storage methods, cryo-compressed hydrogen storage has significant advantages in terms of mass hydrogen storage density, volume hydrogen storage density, hydrogen storage cost, safety and evaporation loss. The key component of cryo-compressed hydrogen storage is cryo-compressed hydrogen storage vessel. The current commercialized type III bottle is mainly designed for normal temperature and high pressure, while the key scientific issues of material and container performance under low temperature and high pressure conditions are not clear. It is of great significance to study the low temperature performance of materials and containers, and to explore alternative materials with low cost and excellent mechanical properties for achieving the goal of the United States Department of Energy's hydrogen storage cost and promoting the extensive commercial application of hydrogen fuel cell vehicles.
In order to reasonably design and optimize the performance of cryo-compressed hydrogen storage tank, the author uses carbon fiber and low temperature resin to prepare composite one-way plate from the material, and then makes the one-way plate into relevant splines for testing. The relevant parameters of the spline are tested in the liquid nitrogen temperature zone, such as elastic modulus, Poisson's ratio, thermal conductivity, etc. According to the design requirements of the tank, select the appropriate winding thickness to wind the cylinder. Substitute the relevant parameters into the numerical simulation software to carry out the numerical simulation of the cryo-compressed hydrogen storage tank. Through the performance test platform of cryo-compressed hydrogen storage tank, the relevant parameters of the storage tank under low temperature and high pressure environment are tested and compared with the numerical simulation results. After comparison, relevant parameters are modified and a reasonable numerical simulation correction model is proposed. It provides guidance for the design and use of cryo-compressed hydrogen storage tanks.
Under the general trend of energy reform and utilization of renewable energy, the key role of hydrogen energy has been becoming increasingly prominent. The IEA report highlights hydrogen as an integral part of net zero emissions, and many countries are developing strategies to incorporate hydrogen into the major energy plans. Hydrogen is an ideal efficient clean energy, which can be used in fuel cell vehicles and other new energy power. In addition, in the field of cryogenics and refrigeration, such as aerospace, superconductivity technology, high-energy physics and other big scientific devices, hydrogen is commonly used as a cryogenic working medium, but also as rocket propellant, and liquid phase can be used as coolant.
In the hydrogen energy industry chain of production-storage-transportation- utilization, compared with gas phase at high pressure, liquid hydrogen has advantages such as high density, low transportation cost, high purity of vaporization and short filling time, which make it more suitable for the large-scale development of hydrogen energy. Liquid hydrogen can also be used as an energy storage medium, providing cold energy and electricity to smooth out fluctuations in renewable energy generation and reduce abandonment of wind and light.
In this article, a model and analysis of energy storage process using liquid hydrogen was established, including purification and liquefaction, liquid hydrogen storage, pressurized vaporization, cold energy utilization, power generation output and other processes, selecting appropriate methods and equipment, systematically contacting all aspects of liquid hydrogen energy storage and application, evaluating its efficiency, economy, environmental protection and expansibility, and comparing it with other energy storage methods, such as thermal energy storage and electric energy storage. Their application scenarios and development prospects were analyzed, seeking solutions on how to rationally and efficiently utilize liquid hydrogen energy storage and reduce costs, so as to provide new ideas for the actual storage and application of hydrogen energy.
Determining ortho-parahydrogen compositions at cryogenic temperatures is an important quality control for liquid hydrogen custody exchange. High orthohydrogen compositions lead to an exothermic reaction resulting in increased boil-off and increased venting losses of liquid hydrogen product by either the supplier or consumer. Traditional methods for measuring ortho-parahydrogen compositions such as hot-wire anemometry, nuclear magnetic resonance, and infrared spectroscopy are typically inconvenient at best. As the number of cryogenic hydrogen systems continue to increase, there is an increased need for flexible, standardized techniques for post processing composition measurements. A Raman spectrometer implemented in the Cryo-Catalysis Hydrogen Experimental Facility (CHEF) has demonstrated incredible flexibility for composition measurements of cryogenic hydrogen flows through a wide range of temperatures and pressures. This article analyses the uncertainty of Raman spectroscopy data of cryogenic hydrogen equilibrated at temperatures in IONEX catalyst. Spectra from hydrogen catalyzed to the equilibrium ortho-parahydrogen composition are processed and compared to expected statistical distributions for method verification.
As a new economical, efficient and feasible high density hydrogen storage method, cryogenic compressed hydrogen has been widely concerned by scholars in recent years. Based on the existing hydrogenation stations at normal temperature and high pressure, this paper proposes a new cryogenic compressed hydrogen refueling process based on liquid nitrogen precooling, which can generate 80K and 35MPa hydrogen, and at the same time this can reduce the loss of hydrogen under the random initial state conditions of the cryogenic compressed hydrogen tank. The main operating modes of the system include compressor cycle, hydrogen cycle precooling, refueling and standby. In order to verify the feasibility of key equipment and the above process, helium gas is used as the working medium to build the above system process. The fabrication of the cold box, compressor and cryogenic tank have been completed. The commissioning of the system is foreseen in the near future.
Vapor cooled polymer composite tanks for liquid hydrogen are a new opportunity for light weight power-system integration into unmanned aerial vehicles. Vapor shielding has the ancillary benefit of pre-conditioning the hydrogen for use by a fuel cell. However, the mass flow rate required by a fuel cell should be matched by the natural boil-off rate of the tank. With limited ability to vary insulation thicknesses, the challenge becomes satisfying the fuel cell consumption in UAV at different mass flow rates when at varying stages of flight from take-off, cruising, and landing. This paper details how batch purging with helium or argon in the vapor cool shielded insulation layer can affect the mass flow rate of hydrogen, to aid in optimal fuel-cell feed rates. A 5-shell vapor cooled shielded tank is used with two layers of insulation including aerogel, and helium or argon, and two vapor channels. A more complete understanding of system-level thermal conductance is determined by measuring mass flow of hydrogen leaving the tank during hypothetical flight missions.
This study is based on a self-developed test device that achieves catalytic performance testing of Ortho-Para hydrogen catalysts in the liquid nitrogen temperature region. The hydrogen samples are pre-cooled to liquid nitrogen temperature and then flow through a packed bed converter filled with Ortho-Para hydrogen catalyst for isothermal conversion at liquid nitrogen temperature. The converted hydrogen samples were finally measured for parahydrogen concentration by a gas chromatograph equipped with a thermal conductivity detector. First, the compressed high-purity hydrogen and the hydrogen produced by electrolysis of water in a hydrogen generator were respectively used as carrier gases for the analysis of the same catalyst to compare the effects of the two types of hydrogen on the results of gas chromatography. Then, the catalysts were filled into the packed bed converters with the same inner volume, and the same reactivation method was used for the converters filled with catalyst samples of different particle sizes, and finally, the effect of particle size on the catalytic performance of Ortho-Para hydrogen catalysts was investigated experimentally. Furthermore, an experimental study on the effect of filling method on the catalytic performance of packed bed for Ortho-Para hydrogen conversion was conducted to compare the effect of loosely filled and tightly filled catalyst samples of the same volume on the catalytic performance. This study can provide relevant experimental data for the design of Ortho-Para hydrogen converters in actual hydrogen liquefaction systems and optimize the design and fabrication of Ortho-Para hydrogen converters.
Achieving the targets set out in the 2015 Paris Agreement requires expanding the usage of renewable power generation globally. The cost of renewable energy is highly dependent on location and countries such as Japan are unlikely to have sufficient renewable power capacity to meet their energy demands. Exporting renewable energy in the form of liquid hydrogen is one means to achieve this.
Without active refrigeration, heat leakage into the tank cannot be avoided. Export-scale tanks (40,000 cbm) typically cannot operate significantly above atmospheric pressure (<0.5 bar), requiring venting of vapour. This venting may not coincide with onboard hydrogen consumption for propulsion, leading to a loss of product. The rate of self-pressurisation is highly dependent on convective boundary layer flows within the liquid which forms a thermally stratified layer close to the surface, enhancing evaporation. The development of thermal stratification remains poorly understood at high Rayleigh numbers and non-uniform, non-steady state heat transfer.
The goal of this project is to investigate the development of thermal stratification and pressurisation in export-scale liquid hydrogen storage tanks, with the aim of informing tank design and shipping operations. Using analytical and numerical methods, this study investigates the effect of heat transfer and vapour removal on thermal stratification in the liquid and vapour phases, and the role of sloshing and jet-mixing in inducing condensation.
Some applications in liquid hydrogen (LH2) research require the availability of hydrogen with a freely adjustable ortho-para ratio. Examples of this are the calibration and qualification of ortho-parahydrogen measurement systems, the establishment of defined arbitrary inlet compositions for sample reactors investigating the performance of ortho-para catalysts, and investigation on the neutron scattering cross section in LH2-based cryogenic neutron moderators.
In this work, a cryostat for the production of stable, arbitrarily adjustable ortho-parahydrogen mixtures is presented. It is part of a new facility at TU Dresden focused on the comprehensive investigation of catalytic ortho-parahydrogen conversion established within the government-funded project HyCat. The system uses a strongly oversized isothermal catalyst bed to ensure full conversion of a continuous hydrogen flow to the equilibrium condition for temperatures between 18 and 100 K and pressures between about 2 bar(a) and 100 bar(a). First experiences with the use of the cryostat were made and operational limits have been demonstrated.
A 1,300 liter-capacity liquid hydrogen (LH2) storage tank has been designed and constructed. The thermal insulation system of the LH2 storage tank is designed to have a boil-off rate (BOR) of 1.5 vol.%/day and a refrigeration system is introduced to achieve zero-boil off (ZBO) of LH2. A multi-stage GM-type pulse tube refrigerator (PT815, Cryomech) is utilized for the refrigeration system. The LH2 storage tank is mainly composed of a radiation shield and an internal reservoir. The aluminum shield is conductively cooled by the first stage of the pulse tube cryocooler and it also equips a vapor-cooled loop for rapid initial cooling. The stainless-steel reservoir has a fin-array to suppress pressure elevation due to the vaporized hydrogen at its top side. The fin-array is cooled by the second stage of the pulse-tube cryocooler and it is made of oxygen-free high conductivity (OFHC) cooper. The fin-array is brazed with the reservoir body and it is designed to have a proper thermal resistance between them. The annular space between the outer shell and the internal reservoir is evacuated down to 10-5 mbar.
Liquid Hydrogen (LH2) infrastructure systems are widely installed in industry where more than 200 systems convert the low pressure LH2 to high pressure gaseous hydrogen (GH2) which is stored in pressure vessels (ground storage tanks) and distributed via a high-pressure manifold as needed, to multiple fueling stations which refuel the onboard H2 tanks of the H2 vehicles (cars, buses, trucks) or hydrogen power industrial trucks (HPITs). The LH2 infrastructure consists of various subsystems with different design and operating pressure and temperature ranges. It is critical to implement test methods which will test each subsystem/component under its worst case scenario. For instance, the worst-case scenario for the ground storage tank, is the maximum operating temperature/pressure case for strength consideration. The worst-case scenario for the tank valve, is the maximum operating pressure and minimum operating temperature for seal material embrittlement consideration. Several examples are presented where the worst-case scenarios are different, for the various components of the subsystem. It is also critical to develop intelligent systems which can utilize the output signal of the various sensors to determine subsystem malfunctioning, and take action that will result in safer and more efficient operation. Several examples are presented, where intelligent controls predict subsystem failure and take immediate action to avoid a dangerous condition.
The Center for Axion and Precision Physics Research is studying the search for dark matter using 12 tesla superconducting magnets. A dilution refrigerator is being used for search experiments, and superconducting magnets, superconducting cavities. The dilution refrigerator requires a stable cryogenic environment using liquid helium. Accordingly, a cryogenic system for a stable supply of liquid helium is to be established. This cryogenic system includes the liquefying, supply, storage, and purification of liquid helium. This article presents the basic design, construction, and operation plans for building cryogenic systems.
The combination of J-T heat exchanger and flow resistance replaces the function of 1 K-pot, which makes dry dilution refrigerator one of the research hotspots. This paper briefly introduces the cooperative working process of J-T heat exchanger and flow resistance, puts forward the principle and method of flow resistance design of dry dilution refrigerator, and studies the effect of different flow resistance on the refrigerator. impact. The results show that the outlet temperature of the J-T heat exchanger must be lower than 3.32 K, and the flow resistance must make the front-end pressure higher than the saturated vapor pressure corresponding to the front-end temperature, usually greater than 1.1 bar. If the flow resistance is too small, the 3He gas will not be able to condense effectively, which will seriously deteriorate the performance of the evaporator and the mixing chamber.
Two Cryogenic Permanent-Magnet Undulators (CPMU) had been developed at the National Synchrotron Radiation Research Center (NSRRC) by using different magnet materials and cooling methods. The PrFe-Bbased CPMU (CU15) was installed in 2019 was cooled by cryocooler, and the NdFeB-based CPMU (CUT18) was installed in 2021 was cooled by liquid nitrogen (LN2) tank. Several benefits were considered in the LN2 tank cooling design of CUT18. The annual operational costs (including maintenance costs) are lower. The mechanical vibration during operation is lower. The PLC-based control units located at non-radiation area that means most inspection could be done during normal operation of accelerator. As the required temperature of magnet is 100 K higher at CUT18 than that of CU15. A large margin of the temperature control on magnets is an advantage for CUT18. The design, manufacture and control of LN2 tank cooling system were performed by NSRRC, which also brings the shortened troubleshooting time. In this paper, we presented the design, control and operation of the LN2 cooling system for CPMU.
The Gamma-Ray Energy Tracking Array (GRETA) is a full 4π gamma-ray tracking detector capable of reconstructing the energy and three-dimensional position of gamma-ray interactions within a compact sphere of high-purity germanium crystals. GRETA will be key instrument for the Facility for Rare Isotope Beams (FRIB) with its unprecedented combination of full solid-angle coverage and high efficiency, good background rejection, and excellent energy and position resolution, and will advance the rare-isotope science at the FRIB. The GRETA Detector Array Sphere will have the capacity to accormodate a total of 30 Germanium Quad Detector Modules (QDM). The 30 QDMs are to be cooled and maintained below 100 K using liquid nitrogen (LN) at all times while the array is in normal operation, and will require regular filling of a LN Dewar on each module.The LN dewar is connected to a common cooling plate to which the detectors are attached. The Dewar is designed to allow the Quad Module to be operated in any orientation with a LN holding time of no less than 12 hours when the detector module is fully powered. An automated LN cooling and refilling system is required to supply LN to the 30 Quad Modules and ensure them maintained below 100 K. Each of the GRETA Quad Modules houses a total of 148 pre-amplifier units within the module, and with the high power consumption of each pre-amplifier, active cooling of the pre-amplifier compartment is required. In addition to the pre-amplifiers, each Quad Module will have 4 digitizer modules attached to it, which generate heat and require cooling as well. The cooling system for GRETA electronics not only removes excess heat, but also provides the required gain stabilization of the electronics systems. A closed-loop liquid cooling system will provide the required temperature stability and dissipate power generated heat. This paper presents design of the LN cooling system for GRETA QDMs and the closed-loop liquid cooling system for GRETA electronics including techincal requirments, design schemes, analyses of heat loads and process parameters, operation modes and so on.
A dynamic simulation model of Central Helium Liquefier (CHL) has been developed by the process simulation software; EcosimPro®. CHL consists of 4 K and 2 K cold boxes to sustain the operation of LINear ACcelerator (LINAC) which is composed of Superconducting Radio Frequency (SRF) cavities installed in the Cryomodules. 4 K cold box is a modified Claude cycle refrigerator, having LN2 precooler with two Brayton Cycle turbines, followed by the series connected Turbines (Tu3 and Tu4), and a Supercritical Helium (SHe) turbine (Tu5) for high thermodynamic efficiency. The product of 125 g/s of SHe is subcooled at the LHe immersed Heat eXchanger (HX) before supplying to Cryomodules, which has its own precooled HX for He II vapor vs. SHe, to have high liquid yield for He II at 2.1 K. Four series connected Cold Compressors (CCs) keep the LINAC pressure at 0.04 bar for the proton beam acceleration. The paper discusses the modeling of CHL, including four CCs. The benchmark of the model against a design specification of CHL and the validation of CC model is also described in detail.
Dynamic simulation of Tokamak superconducting magnet system has been conducted to investigate the cool-down process from 300 to 80 K. The simulation focuses on the cool-down speed variations with respect to the global temperature gradients in the different coil systems; Toroidal Field (TF) coil, TF STructure (TF-ST), Central Solenoid (CS) and Poloidal Field (PF)/Correction Coil (CC) systems. As imposing the maximum temperature gradients dT_max<50 K, the speed should be adjusted, ensuring the limited mechanical stresses due to thermal contractions. So far, the process simulation of Tokamak cryogenic system has been concentrated on the DT operation phase; therefore, it is necessary to revise the model to extend its capability for the cool-down; for example, the thermo-hydraulic properties of Cable-in-Conduit Conductor (CICC) for each coil, mechanical properties of materials for the coil system. The cooldown process is implemented at the helium refrigerator by utilizing LN2 heat exchanger up to 80 K. Its speed is set at -0.8 K/hr as a baseline, which can be controlled by the global temperature gradients in the magnet system. The process will be on hold as dTmax > 50 K and resumed once dTmax < 50 K. At this point, the refrigerator keeps the constant supply temperature of GHe to the magnet. In principle, the speed depends on the TF_ST, which has a massive cold mass within the system. The paper discusses the cool-down processes of the Tokamak and identifies the impact on the speed, dT/dt of each component.
Boil-off gas (BOG) in cryogenic vessels must be vented to keep the pressure below the limit and preserve the safety of the tank. Since liquefaction consumes a lot of energy and BOG in the tank only loses latent heat, it is not economical to vent it directly. Undoubtedly, providing refrigeration power to reliquefy the evaporated gas or subcool the cryogenic fluid is a superior scheme. Therefore, an efficient cryogenic refrigerator is essential to provide sufficient refrigeration power, and the performance of the refrigeration system is determined by the composition of the refrigerant, the design of the refrigeration cycle, and the operating parameters. In this paper, we optimized the working fluid composition and process parameters of the turbine-Brayton cycle in the temperature range of LNG, liquid nitrogen, and liquid hydrogen. Moreover, we proposed and optimized two new processes for the same temperature ranges. The refrigeration cycles are established in Aspen HYSYS, and the optimization is performed in MATLAB using the genetic algorithm. Reasonable constraint parameters and variables are given for the optimizations. The optimal composition of the working fluid and process parameters were obtained by 9 independent optimizations. The performance of the three cycles in different temperature ranges was compared in detail. The results show that the new process has significant advantages over the turbine-Brayton cycle. The refrigeration system can be easily scaled and combined so that it can be arranged in scenarios with different refrigeration requirements. This paper will provide an important reference for zero-boil-off storage of large cryogenic tanks.
We have previously found experimental evidence of several quantum phenomena in oxygen-ion implanted or hydrogenated graphite: ferromagnetism, antiferromagnetism, paramagentism, triplet superconductivity, Andreev states, Little-Parks oscillations, colossal magnetoresistance, and topologically-protected flat-energy bands. In particular, triplet superconductivity results in the formation of Josephson junctions, thus with potential to being used for spintronics applications, in particular in the critical area of quantum computing. Another outstanding feature that we have observed from the temperature-dependent remnant magnetization Mrem(T) measurements is the formation of spin waves.
In this work we are presenting more evidence for the formation of two-dimensional (2D) spin waves in oxygen-ion implanted and in hydrogenated highly oriented pyrolytic graphite. Magnetization measurements were carried out for the temperature range from 1.9 K to 300 K using the Quantum Design Physical Properties Measurement System. Mrem(T) data confirms the formation of spin waves that follow the 2D Heisenberg model with a weak uniaxial anisotropy. In addition, we found that beyond the region showing the 2D spin waves, Mrem(T) goes through a first-order magneto-structural transition from the antiferromagnetic to the ferromagnetic order. This could be the result of reorientation of surface spins around the dislocations and/or domain pinning. We also note that the observed step-like feature of the transition might be due to the coupling between the superconducting the ferromagnetic domains.
The aerospace industry is the last major transportation industry working to implement hybrid-electric technology for propulsion. Nearly exponential growth is occurring recently for electric aircraft, with reportedly with more than 600 vehicles being developed as of 2022. As of Jan 2023, pre-orders for electric aircraft exceeded 8,900 aircraft and $52B sales, even though only a handful of electric aircraft have been certified for flight so far.
The electric-wire-interconnection-system (EWIS) of an electric drivetrain is known to have by-far the largest mass fraction of an electric system, and can be 2-3% by weight of entire aircraft. This paper studies the EWIS of a 40-MW-class electric drivetrain, and compares different wire technologies including cryogenic metals, superconductors, and ‘conventional’ metals at ambient temperatures. The mass and heat loss scaling laws of the components of the electric drivetrain are presented for varying power/voltage/ampacity levels (0-20 kA) and power-wire distribution architectures. Electric power system components studied thus far include metal conductors (Cu-clad-Al (CCA), Al 99.999% ‘hyperconductor’), busbars, current leads, superconducting wires of various materials including (Y,RE)-Ba-Cu-O, tee-junctions, circuit breakers, fault-current-limiters, low/high voltage insulation, and cryoflex tubing. A weight and efficiency analysis of a 40 MW EWIS system will be provided, and material options for will be compared. Some of the complexities of cooling the EWIS system using cryo-liquids or cryo-gases, will be described.
Acknowledgments. This research was funded by the NASA University Leadership Initiative (ULI) #80NSSC19M0125, AFOSR LRIR #18RQCOR100, and the Air Force Research Laboratory/Aerospace Systems Directorate.
Power electronics for electric aircraft applications are necessary components in controlling stator windings independently at high power. The added benefits of using liquid fuel to cool conductors to utilize their high current density has driven power electronics to be cooled by proxy. While small scale semiconductors were negatively impacted by cryogenic operating temperatures, experiencing freeze-out, systems rated for high power applications have not been discussed. In this work we test the performance of IGBT power electronics in temperatures ranges from room temperature to cryogenic temperatures down to 77 K in liquid nitrogen (LN2) with a focus in temperatures estimated for electric aircraft motors using liquid natural gas (LNG) as the cooling medium around 120 K. The performance measures will be determined by its basic ability to turn on and off based on the input signal provided by a function generator. Along with its fundamental testing criteria, we test the quality of the output signal by measuring rise time, fall time, and the quality of the output over the temperature range all within the operating frequency range of 15-20kHz. The experimental data is then collected over a range of operational frequency possible for the given motor design, and we also consider various power output matching a single stator contribution in a full motor design. To date, the electronics have maintained its ability to switch on and off in low power approach down to 120K.
The mechanical stress in the superconducting magnets due to clamping forces and Lorentz forces have been investigated by many researchers. The main issue is a critical current and quench induced by a magnetic field and mechanical strains in the busbars. Unfortunately, much less attention was paid to the mechanical stress and stability of the busbars that power the magnets. The self-induced magnetic field in the powerline busbars is much weaker than in the magnets, so the critical current is higher and not problematic. However, the Lorentz forces are still significant if the busbars are routed close to each other. If the magnet is powered by an AC current, pulsation of the Lorentz forces can be a cause of fatigue damage of the busbars.
In the paper, the powerline busbars of the SIS100 synchrotron magnets are analyzed. The SIS100 synchrotron is part of the FAIR project, realized in Darmstadt, Germany. The fast ramping magnets used in SIS100, are based on NbTi Nuclotron-type superconducting busbars. Four pairs of powerline busbars are routed in the common vacuum envelope with the process pipes providing cooling to the magnets. Due to high demand for magnet control quality, the electromagnetic cross-talk between busbar pairs must be minimized. For this reason, the busbars in each pair are clamped close to each other, while the distance between pairs is equal to 200 mm. The clamping of the busbars in a single pair effectively cancels an external electromagnetic field, minimizing the crosstalk between the busbar pairs.
The special G10 busbar clamps are spaced along the busbar pair at a distance of 45 mm. This design was tested and is used in around 2000 m of the powerline busbars of the SIS100 synchrotron. However, the problem was revealed in the interconnection areas:
Due to the design of the busbar interconnection (soldering), the distances between busbars in the single pairs are different from the standard busbar section (distance of 9 mm) and equal to 25 mm or 50 mm. In the interconnection areas during pulsed powering tests, a significant movement of the busbar was observed, which can cause mechanical fatigue damage to the busbar and powerline failure. The question was: How should the busbars in the various interconnection areas be clamped to achieve fatigue life similar to or longer than the standard powerline section clamped with a spacing of 45 mm?
The numerical study was carried out to optimize the minimum clamp spacing in the interconnection areas. A detailed Nuclotron cable was prepared that contained 23 NbTi superconducting wires around a central cooling pipe made of CuNi. All contacts between wires, between wires and cooling pipe, and between busbars and clamps are included in the model. Three busbar clamp designs were tested:
- with standard with 9 mm distance between busbars, used in powerline section
- with 25 mm distance used near the soldering area
- with a distance of 50 mm used in the soldering area
Each design was tested in a representative section of the clamped busbar pair, with four subsequent clamps included to minimize the influence of the boundary conditions.
After the initial clamping force, the dynamic simulation of the busbars loaded by a few cycles of Lorentz forces was carried out, up to stabilization of the busbar pulsating stresses. Simulations were repeated for various spacings between clamps along busbars in order to find the spacing at which the mechanical stress amplitudes in interconnection areas are equal to stress amplitudes in the standard powerline section.
The areas of the busbars were identified, allowing for an improved clamp design. The maximum stress on the busbar was detected not in the clamp, but in the area next to the clamp.
As a result of all numerical simulations, the dependencies between busbar distance in pair, clamp spacing, and mechanical stress amplitudes were presented and discussed.
Bi-2212 Rutherford cables are under consideration for construction of the next generation of high-field magnets for particle accelerators. The critical current has been increased to a level sufficient for these magnets, but field errors due to magnetization and flux creep is still a concern, especially since these can be higher for HTS materials than Nb-Ti or Nb3Sn. The magnetization and decay of magnetization due to flux creep in a Rutherford cable segment were measured previously. A series of magnetic field sweeps was applied of the form 0 T, 2.5 T, x, 1 T, followed by an 1800 s dwell at 1 T, where x is several values ranging from -1 to 1 T. By doing so, the relaxation of various internal flux penetration profiles is probed, and the implications for the time-dependent magnetization response of an accelerator magnet are examined. In the previous analysis, relaxation rates were found which were lower than in previous measurements of Bi-2212 strands. Here, the analysis of the cable is extended to the wire from which that cable was made. The effects of sample length, microstructure, strand geometry, and cabling on the magnetization and its temporal decay are evaluated.
The CORC® superconducting cables composed of YBCO coated conductors are of great interest for power transmission applications due to many advantages such as high power density, lightweight and low loss. The flowing cold Helium gas can be used to cool HTS cables down to 50 K to significantly improve their current carrying capacity. Coupled electromagnetic-thermal finite element (FE) simulations implemented in COMSOL Multiphysics package were developed to predict the fault current limiting performance and the cooling after the fault of a YBCO cable cooled in flowing He gas. In the simulations, temperature dependence of electrical and thermal properties of all component materials are considered for better accuracy. In order to overcome computational challenges caused by the considerable difference in geometric scale (a few µm for the HTS tape thickness and 10 m for the length of the cable), the model is divided into two separate simulations. The first simulation is performed on the cross-section of the cable to calculate the electric field, power heating and temperature rise in every component of a CORC® cable when a pulse of current higher than cable critical current is applied for about 30 ms, which would be long enough for electrical breaker to shut off the fault. The heating power calculated in the first simulation will be transferred to the second model to simulate the cooling of a 10 m long cable after the fault. Effect of the flow rate of coolants and the thickness of dielectric insulation layers will also be investigated to suggest strategic approaches for optimizing the design of the cable and cooling system for fault current limiting performance.
In this work, we performed studies of quench protection relevant to MgB2 based 3T conduction cooled magnetic resonance imaging (MRI) machine. We modelled a conduction cooled MgB2 whole body, segmented coil MRI design. The overall design had 3T in the bore, with 10 ppm homogeneity in a 49 cm DSV, total magnet length = 1.37m, total conductor length = 121km, operating current Iop = 287 A, critical current Ic = 383 A, and I/Ic = 0.75. We first applied the CLIQ scheme to one coil, with OD 901 mm and winding pack 44 mm thick×50.6 mm high, conduction-cooled, react-and-wind, with 1.7 km of MgB2 strand. The results of coil temperature and current are presented for various protection conditions. These results are compared to those using a quench heater approach (with external dump resistor). A scheme for scaling this approach up to protect the full magnet is then described, and the simulation results presented. An oscillating 100A and 75Hz exciting current generated by a charged 40mF, 0.2µF and 500V capacitor in CLIQ units induces a transition to the normal state of the entire coil winding pack within 7 seconds.
As typical REBCO conductors contain laminated high-aspect-ratio (HAR) thin films, such as the silver, REBCO, and buffer layers, effective modeling is a significant challenge. In this study, the three-dimensional/two-dimensional (3D/2D) mixed-dimensional modeling method is adopted to build a novel elastic-plastic structural mechanics model, which realizes the entire simulation of fabrication and cooling processes and subsequently under tensile loading with multi-step modeling. Based on the cohesive zone model (CZM) and 3D/2D mixed-dimensional modeling methodology, the delamination model is further generated. The models include all the major constituent layers of a typical REBCO conductor. Furthermore, a phenomenological model of the internal strain in the REBCO films dependence of critical current (Ic) was developed based on Ekin power-law formula and Weibull distribution function for analyzing the electromechanical properties of REBCO CC tapes under different deformation modes. Simulation results show that the 3D/2D mixed-dimensional model performs simulations with much higher computational efficiency than the full-3D counterpart while maintaining sufficient accuracy. Multi-step modeling is an effective method for elastic-plastic stress and strain analyses of REBCO conductors during the fabrication and cooling processes and under tensile loads. The 3D/2D mixed-dimensional elastic-plastic delamination FE model based on CZM can be used to study the delamination behaviors in REBCO conductors. The phenomenological model was experimentally verified to be effective in Ic degradation behavior prediction under different deformation modes. The 3D/2D mixed-dimensional method models any number of laminated HAR thin layers in a composite as stacked 2D surfaces, thus, resolving the thickness-dependent meshing and computational problems in modeling such composites with full 3D FE approaches. With a set of appropriate model parameters determined by experimental data for Ic under uniaxial tensile deformation, the proposed model can effectively predict Ic degradation behavior including reversible and irreversible processes in different deformation modes.
Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes are promising for high-energy and high-field applications. In epoxy-impregnated REBCO superconducting windings, due to the weak c-axial strength of REBCO CC tapes, delamination induced by thermal mismatch stress and Lorentz force significantly threatens stable operation. As the epoxy-impregnated REBCO superconducting magnets are composed of multi-layer components with different material properties, however, the stress state of each constituent material is quite different during extremely low temperature and strong electromagnetic field condition. At present, the commonly used numerical modeling methods mainly include the homogeneous orthotropic model and the real fine model. The former can realize the efficient calculation of the overall physical field but lose the local details including interfacial delamination bebavior, while the latter can realize the fine calculation of all the physical fields in the whole domain but cost massive calculation. In this study, delamination behaviour of an epoxy‐impregnated REBCO pancake winding under cryogenics and high magnetic field was investigated through a hierarchical axisymmetric finite element model with main layers of the coated conductor and insulation materials. Firstly, the homogenized superconducting magnets was constructed to estimate the electromagnetic-thermal-mechanical properties at macro scale, and the ‘dangerous regions’ in the macro scale was recognized; secondly, the mechanical response including interfacial delamination described by the cohesive zone model of each turn coil was reconstructed in the micro scale in the ‘dangerous regions’, and homogenized properties was still adopted in the other regions. The accuracy and efficiency of the hierarchical delamination mothed were validated by the refined numerical model. The discussions indicated that the potential risk for delamination failure during cooling increased with the decrease of temperature. If delamination did not appear after cooling, the winding will not be damaged owing to interfacial debonding under self-field. However, the risk of delamination failure increased upon increasing the transport current under a strong background field. The presented hierarchical numerical modeling method is promising for evaluating the risk of failure in large scale HTS magnets.
With the increasing demand of accelerators for high-energy particles, it is necessary to develop ECRIS (electron cyclotron resonance ion source) with compact structure, small volume, and high energy. ECRIS, which generates highly charged particles, is an essential component of heavy ion accelerators and heavy ion therapy equipment. A new S-shaped hexapole structure was proposed in 2016, which can greatly reduce the size of ECRIS magnet [1-2]. The S-shaped hexapole can simplify the distribution of interacting Lorentz forces in ECRIS superconducting magnet and help to increase the required axial field in ECRIS. However, the manufacture of S-shaped coils is very difficult, and it is also difficult to apply pre-tightening force at the end of the S-shaped coil. There is no reference on the manufacture of the new type superconducting hexapole. Two designs of the S-shaped coil and their special skeleton will be presented in this study. Based on the two designs, two coils using NbTi wire were developed in this study, including a test coil and an S-shaped hexapole prototype for 14.5 GHz ECRIS. The test coil is designed with a skeleton with slots at both ends to realize the winding of the S-shaped coil. The S-type hexapole test coil is wound with only one cable, realizing continuous and uninterrupted winding from inside to outside and from outside to inside. The prototype coil uses the skeleton slotted at one end to further reduce the size of the S-shaped hexapole. Both the fabrication processes and the cold test results will be presented in this study.
MgB2 based superconducting planar undulators are of interest for future electron storage rings for synchrotron radiation by virtue of their higher temperature operation margin with higher stability. In this work, an undulator winding consisting of twelve small pancake coils wound with multifilamentary MgB2 strands was fabricated and tested in liquid and gaseous He, from 4.2 K – 20 K. The coil had a period of 14.4 mm, and it was 5 mm wide and 4.8 mm thick. A critical current (Ic) of 325.7 A was achieved at 4.2 K, and a maximum field of 1.16 T was measured at 314.2 A (extrapolating to 1.19 T at Ic). Finite element modeling (FEM) was performed and validated by the experimental results. Subsequently, modeling has been extended to a 1-meter-long undulator. The magnetic field was measured as the hall probe was translated along the beam axis with an applied current of 14.8 A. The spatially alternating field was asymmetric, with 0.116 T measured in the positive domain and 0.056 T in the negative domain. The maximum field was larger in the positive direction than the negative; the difference is due to the broken symmetry, i.e., the end effect. Coil measurements at the different temperatures gave an almost flat I-V curve following an inductive voltage offset in the beginning. FEM results for the 1-meter undulator indicated that the field of 1 T can be achieved at 10-15 K operation with some modest further development. Operation in this temperature range allows a larger thermal margin and conduction-cooled operation.
The U.S. Air Force has wide ranging needs for electrical energy storage systems. Superconducting magnetic energy storage (SMES) devices offer attractive and unique features including no theoretical limit to specific power, high cycling efficiencies and charge/discharge rates, and virtually no degradation with cycling. The mass specific energy density (MSED) of SMES systems however falls short of many needs. In this study we examine the electromagnetic upper limit on SMES energy densities achievable using present day technology and future technology advancements; especially application of RE-Ba-Cu-O tapes. We limit our investigation to the constraint that the current density puts on the solenoid as a function of magnetic field. We find two geometries that possess particularly high MSED: the pancake solenoid and a single wall hoop solenoid. We demonstrate that MSED for both geometries follow a power law with respect to energy where $ε∝E^{1/3}$. These solenoid geometries set the upper possible limit as to what can be achieved in terms of MSED and should inform future design and application goals for aerospace applications.
A superconducting multi-coil magnet system has been designed, analyzed and optimized, serving as demonstrator for a high filed Magnetic Resonance Imaging (MRI). This work focuses on the design and optimization of superconducting magnet, cryogenic cooling and cryostat systems, as well as key components manufacture and verification.
The NbTi magnet system with multi-coils design has been optimized by balancing magnet performance, stability and offered field quality, against material- and cooling cost. The zero boil-off liquid He-cooled and conduction cooling system operated at 4.2 K, are both designed, analyzed and compared. For the cryostat, the space from inner surface of magnet to the room temperature bore should be kept narrow to maintain optimal field amplitude and homogeneity. This leads to the challenge of reconciling the mechanical constraints imposed by the coil geometry with the thermal insulation requirements. A straightforward structural elements is designed but with a high heat in-leak, while a local reinforced structure is also proposed and analyzed to achieve same space with less heat leak but with some manufacture difficulties. Here, the optimized design of the magnet system and its analysis (e.g. magnetic field, mechanical stress, thermal budget, etc.) are presented.
In the practical application of high temperature (HTS) REBCO coated conductor (CC) tapes, such as epoxy-impregnated or no-insulation (NI) coils, they can experience radial and transversely applied stress due to the large Lorentz force, thermal stress induced by the difference in coefficient of thermal expansion (CTE) among constituent layers which can result in delamination damage and negatively affect its performance during operation. To overcome this challenge, the delamination strength of CC tapes should be characterized mechanically and electromechanically, as delamination mechanisms often cause abrupt and irreversible degradation of the critical current (Ic). This study focuses on analyzing REBCO CC tapes subjected to transverse tensile/compressive stress at 77 K and self-field to understand the mechanisms behind delamination failure and identify the electromechanically weak points in the multilayered architecture of the practical REBCO tapes. The electromechanical delamination strength of two REBCO CC tape samples was determined using a wide Cu anvil and a continuous Ic measurement system, which precisely observes the Ic degradation behavior of the CC tape. The system allows continuous transverse loading to be applied to the sample while the current flow is simultaneously measured. This setup is crucial in preventing catastrophic failures, as even a slight change or damage in the CC tape can trigger a failure in its application. Statistical analysis was used to distinguish the intrinsic strength of the CC tapes from external factors. Delamination schematics were also generated based on the morphology of the delaminated sample, which further explains the rapid drop in Ic of each coil. It is crucial to prioritize the prevention of delamination in HTS REBCO CC tapes as it negatively impacts their performance during operation.
Acknowledgments: This work was supported by KEIT grant funded by the Korean government (MOTIE) (Grant No. 20020421). It was partially supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2022M3I9A1076881).
Modern and versatile, magnetic laminates have found a multitude of industrial applications. This work explores the structure and properties of these materials, exploring their utilization in transformers, electric motors, and protection systems. A laminate was constructed of “E” type glass fiber with a magnetite-filled epoxy matrix. The objective was to develop a soft ferromagnetic laminate composite with improved mechanical properties, especially fracture strength, and toughness. We made composites with varying levels of magnetic particle fill fractions and then measured the mangetic saturation and permeability as a function of temperature. We also measured the core losses and eddy current losses at 77 K at frequencies from 45 Hz to 200 Hz. We measured the mechanical properties at 77 K and compared the results at various fill levels to those of a control composite made with Fe as the magnetic phase. The results of these studies will pave the way for optimizing and modifying its magnetic properties. This research lays the foundation for the development of cutting-edge laminates that can perform even in cryogenic conditions.
It is well known that during the service life advanced polymer composites may be exposed not only to complex mechanical loading but also to harsh environmental conditions. In applications such as aeronautics, automotive, wind turbine blades, composites undergo frequent exposure to sub-zero and even cryogenic temperatures. This may lead to initiation of micro-damage in composites and premature failure of structures. To anticipate these events, one needs to understand the behavior of composites and be able to predict degradation of mechanical properties in sub-zero environment.
In the current work, the mechanical properties and damage initiation/accumulation in woven glass fiber-reinforced epoxy (GF/EP) composites were studied at room temperature as well at temperatures below zero. To evaluate influence of sub-zero environment on mechanical performance of GF/EP laminates two types of test campaigns were carried out: 1) long term exposure of material to liquid nitrogen environment followed by tensile tests at room temperature; 2) tensile tests in sub-zero environment of unconditioned specimens. The quasi-static tensile tests were performed to measure elastic modulus of the composites while loading-unloading experiments were performed to monitor initiation (and accumulation) of micro-damage and its influence on the stiffness of GF/EP laminates.
The results on cryogenic damage and fracture in the laminates are discussed with focus on degradation of properties of GF/EP composites crucial for their use in structural applications: strength, stiffness, damping. The evaluation of different epoxy system formulations with respect to the damage initiation and tolerance in low temperature conditions is carried out. To analyze and demonstrate damage tolerance of GF/EP subjected/tested at different environments, the predictions of stiffness degradation with respect to the induced damage is done by means of analytical modeling.
High entropy alloys （HEA）have high strength, toughness, hardness, and corrosion resistance, and are promising as engineering structural materials for low-temperature applications. In this work, high-entropy alloy CoFeCrNiAl0.05Ti0.05 ingots were prepared by vacuum melting, followed by cold rolling and heat treatment processes to produce samples, which were tested by an electronic universal testing machine at 77 K for their low-temperature mechanical properties. The tensile fracture morphology of CoFeCrNiAl0.05Ti0.05 was observed by the scanning electron microscope(SEM) and the microstructure was examined by X-ray diffractometer(XRD). The test results show that the annealing treatment resulted in a reduction in strength and an increase in plasticity of the high entropy alloy CoFeCrNiAl0.05Ti0.05. In the tensile test, the high entropy alloy at low temperature has higher strength and elongation than at room temperature. This shows that high entropy alloy CoFeCrNiAl0.05Ti0.05 have the potential to perform as it should at low temperatures.
In recent years, polymer/ceramic composites with high thermal conductivity have been widely used in microelectronic devices, superconducting magnets and aviation, and further improving their thermal conductivity is a great challenge. In this study, spherical alumina nanoparticles were modified with 3-aminopropyltriethoxy-silane (APTES) successfully. Furthermore, the modified alumian(M- Al2O3)/Epoxy and graphene/(M- Al2O3)/Epoxy composites were prepared and their properties were tested in the temperature range of 70 K-300 K. The results showed that the thermal conductivity of the composite with 1 wt% graphene and 60 wt% (M- Al2O3)/Epoxy is 13 times higher than that of pure epoxy at 70 K, which indicates its application prospect in thermal interface materials.
Keywords: thermal properties; polymer-matrix composites; low temperatures
The addition of different insulating, non-reactive nano-phases to YBa2Cu3O7-x (YBCO) superconductor thin films improves current density by combining different flux pinning mechanisms. Additions of BaZrO3, BaSnO3, and BaHfO3 nano-rods has been shown to have positive effects on flux pinning and the resulting current densities attained. In particular, BaHfO3 is an attractive addition since it has less lattice mismatch with YBCO when compared to the lattice mismatch of BZO and YBCO. This research explores the impact of calcium doped YBCO buffer layers (Ca0.3Y0.7Ba2Cu3O7-x) on the BaHfO3 doped YBCO film layers, for multilayer films that are produced by pulsed laser deposition. The combination of calcium doped YBCO buffer layers between BHO doped YBCO layers impacts film microstructure and performance of current density and flux pinning. Current density and pinning force over a wide landscape of 65 – 5 K with applied field of 0 -9 Tesla will be presented for these films.
Utilizing insulating nano-phase materials, such as BaZrO3 (BZO) in YBa2Cu3O7-δ films has been shown to increase flux pinning and current density. However, the defective BZO nanorod interface, resulting from its lattice mismatch with YBCO, prevents obtaining optimum pinning force. This research explores the effect of Ca doped YBCO space layers in the multilayer composite film, on the BZO nanorod / YBCO interface, on films produced by pulsed laser deposition. Magnetic current density and pinning force results at fields ranging from 0 – 9 Tesla, will be presented for both high temperature (greater than 65 K), mid temperature (less than 65 K down to 30 K) and low temperature (less than 30 K). These ranges are important for various applications, such as cables and fault current limiters at high temperature and low field, motors and generators at mid temperature and mid field, and NMR and fusion at low temperature and high field.
It is discovered heredity in physical properties in HTSC-thick films after processing HTSC-powders by method of the electromagnetic separation (EMS) . The method was developed for EMS HTSC-powdered superconductors suspended in liquid nitrogen in alternating magnetic field.[1] In the thick film deposition process HTSC is simply heated and "painted" on to the substrate and then fired in a furnace. The main reason for critical current degradation in bulk high-T samples is the grain boundaries, impurities, ballast-phases, and structural defects. Unfortunately, even the most advanced techniques commercially available are unable to produce homogeneous HTSC powders. The EMS-method allows statistical improvement in the uniformity of HTSC powders by decreasing the quantity of defective zones in the separated powders, the number of non-valid phases, admixtures and thus to increase the Tc, Icr (critical current).At the same time, ∆TC- (width of the SC-transition) is being decreased. After separation of the HTSC- powders the concentrate has been saturated with oxygen and is receiving superconductivity. This is in contrast to the tail fraction of the YBa2Cu3Ox powders, which exhibits the tetragonal structure (x < 6.5%) and shows an absence of a superconducting transition throughout the entire temperature interval. Three YBa2Cu3Ox -thick-films by the paint method on the MgO substrate from the source material, the separated high-quality concentrate, and the low-quality remnant (tail) had been produced. The films exhibit different structural and electrical properties, in particular: Icr, and ∆Tc. For example, in the films YBa2Cu3Ox, that was made from the high-quality concentrate ∆Tc- the width of the HTSC-transition, is decreased from 5-7 K to 1-2K.
Reference:
1. E.L. Broide, Method of Separating a Superconducting Fraction From a Mixture, US Patent 5,919,737, Ju1,6 ,1999
The terminating network of low-frequency pulse tube refrigerators consists of a reservoir and main orifice valve. Taken together, these components represent an acoustic impedance that determines how much acoustic power is delivered from the compressor to the refrigerator. The volume of the reservoir, flow resistance of the valve, and frequency of the acoustic oscillations are today chosen by manufacturers to maximize the cooling power available at the cold heat exchanger when it is at its base operating temperature, often near 4 K. At such low temperatures, conditions within the regenerator(s) of the refrigerator make the optimal impedance of the terminating network relatively high. However, during cooldown the optimal impedance of the terminating network is much lower, and a pulse tube refrigerator with static network impedance is unable to accept much of the power available from the compressor because the impedance matching between compressor and refrigerator is poor. By adjusting the network impedance of a two-stage commercial pulse tube refrigerator, we demonstrate that the cooling power available at temperatures higher than the base temperature can be substantially increased. For example, at 295 K we have increased the cooling power of the first and second stages from 197 W to 342 W and from 63 W to 116 W (respectively). Although the greatest increases to cooling power occur near ambient temperature, acoustic impedance matching still provides large relative increases to cooling power at temperatures just slightly above the base temperature. Cryostats may be rapidly cooled by dynamically adjusting the network impedance at all temperatures during cooldown. For 4 K cryostats, improvements to cooldown speed using acoustic impedance matching are further enhanced by thermally connecting the first and second-stage heat exchangers of the pulse tube refrigerator before the base temperature is reached.
Closed-cycle cryocoolers have become an important cooling tool for scientific research at low temperatures [1]. Among the family of regenerative cryocoolers, GM-type pulse tubes (PTC) in particular stand out because they have no moving mechanical parts at cryogenic temperatures. This characteristic makes them ideal candidates for cooling vibration-sensitive applications that also require extended service intervals. The working principle of PTCs relies on the cyclic pressure waves of Helium gas at relatively high pressure differences around 1 MPa. These pressure levels are commonly provided by dedicated Helium gas compressors, which represent the main unit of energy consumption in the cryo system with input powers ranging from 1 kW to above 10 kW.
Due to rapid developments in quantum technology there is a fast growing demand for low power, highly mobile and minimum maintenance cooling systems at 4 K for optical quantum components, e.g., single photon detectors, sensor arrays or single photon emitters and small superconductive electronic circuits. Here we present a combination of the smallest so far reported 4 K ‘PTC Susy’ [2] driven by an oil-free low power compressor technology ‘IGLU’ achieving cooling powers necessary for typical optical quantum components below 4.2 K. The IGLU compressor is based on a mechanism with hydraulically driven metal bellows, providing minimum maintenance and maximum mobility with a miniature footprint [3]. With an input power as low as 1 kW the compressor is air cooled and can be supplied by single phase power sockets. Here we report the performance of the SUSY PTC when operated with the IGLU compressor. This combination reaches the physical minimum temperature of 2.2 K at no load, and a cooling capacity of 240 mW at 4.2K, with the compressor operating at maximum speed at 1.3 kW input power. At 3 K the cooling capacity still reaches 80 mW, relevant in particular for cooling quantum optical components. The coefficient of performance reaches values of up to 185 mW/kW, which is among the highest currently reported values for small to medium power pulse tubes.
In summary, this closed-cycle cryocooler compressor combination provides a unique miniaturized, energy efficient and mobile cooling tool for applications at 4K and below.
[1] R. Güsten, et al., Nature 568 (2019) 357-359.
[2] B. Schmidt, M. Vorholzer, M. Dietrich, J. Falter, A. Schirmeisen, G. Thummes, "A small two-stage pulse tube cryocooler operating at liquid Helium temperatures with an input power of 1 kW", Cryogenics 88 (2017) 129
[3] J. Höhne, “High efficiency, low frequency linear compressor proposed for Gifford-McMahon and pulse tube cryocoolers“ AIP Conference Proceedings 1573, 1242 (2014)
Cryomech has been continuously improving the cooling capacities and energy efficiencies of its 4.2 K two-stage pulse tube cryocoolers. The 2.7 W at 4.2 K two-stage pulse tube cryocooler (Model PT425) was developed and introduced by Cryomech in 2021, which, at the time, was the largest, commercially available, 4 K pulse tube cryocooler. Our newest model, the PT450, has been successfully developed, providing a minimum of 5.0 W at 4.2 K on the 2nd stage with 65 W at 45 K on the 1st stage simultaneously, operating on either 60 or 50 Hz power. The PT450 answers the market’s need for the continuing development of large cryogen-free dilution refrigerators, superconducting magnets, helium liquefiers and other applications requiring large cooling capacities at 4 K.
In addition, a new helium compressor (Cryomech CP3000-Series) has also been developed to provide sufficient helium flow for the PT450 and other large cooling capacity cryocoolers. This new model also allows multiple cryocoolers to operate on one compressor. The CP3000-Series is the largest commercially available helium compressor for the Gifford-McMahon and pulse tube cryocooler market.
The development of the PT450 cryocooler, its cooling performance and experimental results will be presented in this paper.
Traditional Gifford-McMahon cryocoolers are operated with an integrated rotary valve which regulates the compressed Helium supply and return into the cold head. Theory predicts that 50% of the input energy is lost in this rotary valve. In this work we removed the rotary valve from a Sumitomo RDK-101G cold head and drove the Gifford-McMahon cryocooler in Stirling mode directly with a slow-moving metal bellows compressor at around 1.2Hz. We could demonstrate that the energy efficiency of the cryocooler system improves substantially. As a result, we were able to operate this cold head with 650W of total electrical input power with cooling powers of 140mW @ 4.2K on the second stage and no- load temperatures of below 40K on the first stage. The experimental set-up as well as further sources of inefficiencies are discussed.
In order to meet the requirements of weight, vibration, and size in the field of infrared imaging, Lihan Cryogenics has developed a lightweight and compact free-piston Stirling cooler, which weighs only 260g (with built-in electronic controller and active balancer). The cooler system consists of a gas-bearing moving magnet compressor and a low-temperature rod-less displacer. This is also designed to be integrated with industry-standard dewar. Furthermore, in order to reduce vibration, an active Vibration controller is developed, which uses an active motor on the same axis as the compressor piston to offset the vibration. The refrigeration performance under different heat dissipation and working temperatures is experimentally tested. The test results show that the cooler acquires 0.5W cooling capacity at 77K with 14W power consumption, and the power consumption of the active vibration controller is less than 1W.
The pulse tube cooler has the advantages of low vibration, high reliability, and no moving parts at the cold end. However, the poor phase modulation capability and acoustic power dissipation in the phase shifter limit the improvement of its efficiency. Lihan Cryogenics has reported the development of a Stirling pulse tube cooler using ambient displacers. The cooler consists of a moving magnet compressor with dual-opposed pistons and a co-axial cold finger. Ambient displacers are employed to recover the expansion work, increase cooling efficiency, and achieve a relative Carnot efficiency of 26%. This article presents recent advances in this type of cooler. To further reduce manufacturing difficulty, the displacers adopt rod structure, thus lessening the requirement of the supporting spring stiffness and achieving higher reliability. The room temperature displacers are of dual-opposed configuration, and their axis is crossed with the compressor piston axis, which leads to low vibration, less flow resistance, and reduces the difficulty of assembly and production. Typical experimental tests show that compared with the cooler using inertance tube phase modulation, the cooler's power consumption using the new ambient displacer structure is reduced by 24% when the cooling capacity is 60W at 77K.
GM cryocooler is characterized by high refrigeration efficiency and high reliability. Its mature manufacturing line makes it widely used in the temperature zone below liquid helium, such as MRI and cryopump. However, the cooling performance of the cryocooler will be weakened by the secondary flow and the natural convection when the cryocooler is installed horizontally. The influence of secondary flow and natural convection on the cryocooler will be strengthened as the dimensions of the cryocooler increases and the operation frequency decreases. Moreover, the performance of the GM cryocooler with large cooling capacity at the liquid helium temperature zone will be seriously degraded after the installation direction is converted from vertical to horizontal. The cooling capacity of KDE420 GM cryocooler produced by CSIC Pride Cryogenic Technology is decreased from 2.1W@4.2K to 1.6W@4.2K with 23.8% attenuation after its operation direction turns horizontal. Therefore, in the present study, we were committed to carrying out effective process to reduce the influence of operation direction and improve the cryocooler’s cooling performance. By adjusting the size and improving the manufacturing process, the cooling capacity of the KDE420 increases from 1.6W to 2.2W while its operation direction is horizontal. The performance of KDE420 was improved by 37.5% and showed no degradation after 320 hours of horizontal operation.
Liquid hydrogen (LH2) production has predominantly been performed in the past by large gas separation facilities primarily to take advantage of economies of scale and available utilities and commodities such as liquid nitrogen for pre-cooling. With the expanding hydrogen economy, the increased need for LH2 production and storage will drive industry toward smaller liquefaction plants where localized production, storage and use can be realized. A one tonne per day (1TPD) hydrogen liquefaction plant (HLP) has been designed to achieve localized, efficient LH2 production, on-demand, in remote locations or any location advantageous for use in transportation, where complicated logistics, with its associated costs and evaporative losses in transporting LH2 are eliminated or minimized. The chief advantages of the HLP are safety, reliability, modularity, low cost, lack of restrictions on site location, and ability to make practical use of renewable energy. At the heart of the 1 TPD HLP is the liquefier which utilizes a closed-loop helium brayton cycle where temperatures well below the H2 liquefaction temperature can be realized. LH2 is then stored and maintained at zero loss or densified with a helium side stream taken from the refrigeration cycle. The system utilizes helium at low pressure, making the HLP inherently safer than most other H2 liquefaction cycles currently in use. The liquefier is relatively small with few major components/equipment housed inside the vacuum vessel. Therefore, the simplicity of the system increases reliability, affords a high degree of automation, and facilitates ease of maintenance in order to reduce potential downtime. The HLP is also scalable to provide either higher or lower production capacities per unit or multiple units can be placed in parallel or used to cool mega-scale LH2 storage tanks. Without the LN2 pre-cooling, the HLP can be located in remote areas wherever there is available electricity or where local electricity production capacity exists, such as in natural gas fields. The LH2 produced by the HLP can be used across various markets, including car, truck, aircraft, and rail refueling as well as shipboard bunkering applications, many of which are best serviced by use of local LH2 production and storage. The HLP is designed for either liquid-to-gas applications, such as that used for many cars and trucks, or can be operated in liqud-to-liquid transfer as required for future vehicles using onboard LH2 tanks or to dispense to tanker trucks. Lastly, a significant advantage of small-scale LH2 production is due to the relatively low energy requirement and the economical use of renewable energy, feeding back electrical power to the grid during times of low hydrogen production.
With the energy transition ongoing, the demand for small quantities of liquid hydrogen available at any time for testing liquid hydrogen equipment and technologies is growing. Industrial liquefier technologies are focused on large quantities and downscaling is not efficient due to the turbines used which will decrease in performance when scaling down. Therefore, several initiatives have started to develop small-scale hydrogen liquefiers in which the liquefaction is achieved by using a two-stage cryocooler. The main drawback of this concept is the low overall efficiency and high costs of the liquefaction process due to the COP and costs of the two-stage cryocooler, respectively. Further, the liquefaction capacity is limited to about 1 - 2 kg/hr.
The EHLAS (Economic Hydrogen Liquefaction And Storage) project aims to develop an efficient and affordable lab-scale hydrogen liquefier. To obtain this, a liquefier concept is developed that is based on a single-stage cryocooler, Joule-Thomson expansion and a recirculation loop of hydrogen gas with heat exchanger and a compressor to improve the efficiency and reduce the costs of the liquefaction system. With the current design, a liquefaction capacity of 5 - 6 kg/day can be reached.
This paper summarizes the status of the EHLAS project. It discusses the hydrogen liquefier concept, the design of the main components - compressor, heat exchangers, Joule-Thomson valve and storage vessel and liquefier performance.
A mobile hydrogen liquefaction and storage unit has been developed to demonstrate the liquid hydrogen (LH2) value chain including hydrogen production, liquefaction, storage, transfer, and recovery. This unique LH2 technology demonstrator, or LS20 mobile system, is one of the primary systems for a multipurpose LH2 test platform that tests controlled storage and zero-loss transfer methodology. The LS20 system has been designed, fabricated, and tested at GenH2 Corp. The system consists of an electrolyzer, gas precooler, Ortho-Para hydrogen converter, cryocooler-based hydrogen liquefier, portable LH2 storage tank, ultralight LH2 fuel tank for aviation application, safety devices and sensors, automated venting system, and associated sensors, instrumentation, and control system. The LS20 system was successfully demonstrated by continuous hydrogen liquefaction according to the design specification with help of an automated control system and maintained LH2 at a desired level without boiloff loss. In addition to liquefaction and controlled storage of LH2, zero-loss LH2 transfer, boiloff gas recovery, and re-liquefaction were successfully demonstrated with the LS20 mobile system. The results provide proof-of-concept data for future LH2 infrastructure design as well as the critical LH2 refilling and servicing methodology for many hydrogen mobility applications. The system design, fabrication, operational methodology, and test performance results are discussed in this paper.
Currently, there is a great need for testing capabilities for material samples and components in LH2. This includes low temperature compatibility at 20 K, H2 compatibility and possible degradation or permeation effects. The test environment required for this is challenging and quite costly due to LH2 supply. Therefore, an alternative test concept was developed that works autonomously. The required amount of LH2 (typically 2 - 3 l) is generated directly on-site by simple condensation. This is achieved with a power-controlled cryocooler (115 W @ 80 K, 18 W @ 20 K). A cylindrical pressure vessel with an inner diameter of d = 108 mm and a length of approx. 500 mm designed for 0 to 20 barg is used to hold the LH2 bath and the samples. The cryocooler and the sample tube are installed in a common vacuum cryostat and are thermally coupled at the lower end. At the 20 K level, thermal coupling is achieved by a sophisticated thermo syphon arrangement. Hydrogen is taken from a pressure reservoir, pre-cooled at the cryocooler 80 K level, finally injected and liquefied within a couple of hours.
With the growing interest in hydrogen as one pillar of the future energy economy, the relevance of hydrogen liquefaction for storage and transportation is increasing rapidly. However, the liquefaction process still offers much potential for improvement in terms of cost and efficiency. One obstacle on the way to more cost- and energy-efficient liquefiers is the uncertainty associated with the dimensioning of the ortho-para converters. Literature data on the existing ortho-para catalysts stem mainly from the 1950s and 1960s and are partly inconsistent. Therefore, a new facility for the comprehensive investigation of catalytic ortho-parahydrogen conversion was set up at the TU Dresden as part of the government-funded HyCat project. It enables the testing of catalysts in the whole operational range of ortho-para converters in modern large-scale liquefaction plants by allowing the independent variation of temperature, pressure, flow rate, inlet ortho-para ratio, and sample reactor internal geometry. The setup has been tested and validated. It can now be used to produce new high-quality data sets on the performance of the commercial catalyst IONEX (hydrous ferric oxide), for the qualification of alternative catalysts, and for gaining a deeper understanding of the reaction kinetics involved.
Cryogenic boil off from liquid hydrogen can harness the endothermic para- to orthohydrogen quantum state conversion for refrigeration. Ferrimagnetic catalysts such as Fe2O3 are utilized to accelerate the rate of parahydrogen conversion to maximize the rate of cooling. However, the extent of conversion and amount of cooling deliverable is limited by the size of the catalytic converter in the cryogenic cold box. Externally applied magnetic fields can augment catalyst activity to deliver larger cooling loads with smaller parahydrogen catalytic converter sizes. The degree of magnetic enhancement is highly sensitive to the catalyst material, temperature and magnetic field strength and requires experimental measurement to refine the underlying mechanism. This study investigated the influence of an externally applied magnetic field on the conversion rate of para- to orthohydrogen at cryogenic temperatures. The rate of conversion was measured at magnetic fields of 0.25 T and 0.5 T and conducted over a Fe2O3 catalyst. Further experiments assessed the reversibility of the magneto-catalytic effect by measuring the impact of an applied magnetic field on the ortho- to parahydrogen conversion, which is encountered during hydrogen liquefaction. The results contribute to understanding the basic physics of ortho-parahydrogen conversion catalysts.
Cryostats for research and testing applications have been designed and implemented successfully for many years. The design features are selected to provide for the desired functionality with the most efficient operation, particularly with regard to refrigeration requirements. In this paper we introduce engineering figures, calculated table-plots and representative equations for the design, configuration, and thermal optimization of advanced cryostats for different typical cold masses in current and future applications. For example, the cold mass contained and thermally isolated in the cryostat could be a quantum apparatus, test specimen for property characterization at low temperatures, in-space simulation for instruments, thermo-fluidic research, or a superconducting device, to mention a few. All these must operate at cryogenic temperatures while providing all functional interfaces for power and instrumentation to obtain the required data. Also included are in-depth discussion of the design methodologies for crucial cryostat components including: 1) the light-weight structure of cold mass supports and allocation of thermal anchors to the best temperature spots, 2) designs of MLI systems and associated cost-efficient minimization of radiation heat via intermediate shields, 3) the sophisticated structures required to house heavy current leads or RF couplers while also preventing heat flows from reaching the cold mass in cryostats with active cold masses such as SC magnets or SRF cavities.
To demonstrate the integration of these technologies into cryostat design, we also present several cryostat configurations suitable for various cooling methods including cryogen baths, cryogen-free cryocoolers, continuous cryogen flow, and below 1-K with dilution-demagnetization. Lastly, we describe a few special cryostat designs that are suitable for unique testing requirements such as laser windows and horizontal loading.
Molecular hydrogen occurs in two forms, the so-called ortho-hydrogen (parallel alignment of the nuclear spins) and para-hydrogen (antiparallel alignment of the nuclear spins). At a temperature of 293 K and above, hydrogen has 75% of ortho- and 25% para-content. The content of para-hydrogen increases with falling temperature. At a temperature of 20 K almost 100% para hydrogen is present. While hydrogen is cooled down and liquefied the exothermic natural conversion starts, but much slower than the liquefaction itself. However, the conversion can be accelerated by using a catalyst.
To avoid an unintentionally evaporation due to the exothermic ortho to para conversion it is important to verify that the conversion is completed before the liquid hydrogen is stored, transported or used. It is state of the art to accelerate and to ensure a complete conversion by using an oversized ortho/para catalyst. However, the activity of the catalyst decreases over time. Therefore, a continuous in-situ measurement of the ortho/para ratio can contribute to effective use of the catalyst. Furthermore, the amount of catalyst can be reduced and hydrogen losses due to the unintentional evaporation can be prevented by verifying and adjusting the ratio.
The measurement systems which are commercially available do not allow an in-situ measurement of the ortho/para ratio of liquid hydrogen. Therefore, a measurement system based on Raman spectroscopy is currently being developed at the ZEA-1. First tests with the measuring system show promising results for normal hydrogen and 100% para-hydrogen on a laboratory scale.
In a next step, the laboratory set up will be redesigned in a way that a selective mixing of converted and normal hydrogen allows the measurement at any concentration in real time. This enables to optimize the measuring system and, among other things, to characterize catalysts.
The aim of these investigations is to develop a compact measuring system that can be used in research and industrial applications and reliably measures the ortho/para concentration of liquid hydrogen in-situ.
The Einstein Telescope (ET), as the planned third-generation, underground gravitational-wave observatory for Europe, will increase the sensitivity compared to the current advanced detectors (Virgo, LIGO, KAGRA) and expand the frequency band to lower frequencies. Proposed as an equilateral triangle with 10 km long vacuum pipe arms, the Einstein Telescope will consist of three laser interferometers for high (HF) and low frequencies (LF) each.
The main optics of ET-LF will be cooled to cryogenic temperatures below 20 K and the whole system, consisting of the beam pipes, the suspension towers and the cryostat containing the mirror, requires high to ultra-high vacuum conditions. Residual gas has to be reduced as much as possible to avoid e.g. thermal or optical noise and due to the fact that gases like water will be adsorbed as frost on the cryogenic mirror surface and thus degrade its optical performance.
In order to fulfill the vacuum related requirements and to consider thermal radiation aspects from the warm interferometer to the cryogenic mirror, the use of tailor-made in-situ cryopumps is envisaged. Simulations at KIT, performed with the in-house Test Particle Monte Carlo code ProVac3D and a simplified model of the system, considered the main gas sources from the neighbouring systems (coming from the outgassing steel surface along the entire beam pipe, the warm tower with the mirror marionette, and the adjacent tower) and the sinks by pumping stations distributed along the pipe arms, the cryogenic pump section close to the mirror and the cryogenic mirror environment. These simulations showed different needs for the pumping of hydrogen (to lower the residual pressures) or heavier species like water (to lower the frost formation on the cryogenic mirror surface) – depending on the position in the interferometer related to the mirror. With these findings, the development of a pumping concept was worked out.
In parallel, the outgassing rates of the inner walls of the beam pipe tubes, influencing strongly the vacuum pumping demands, have been investigated experimentally with a dedicated outgassing facility at KIT in order to support the decision process for different material options.
This paper describes the developed pumping concepts, utilizing cryogenic pumps integrated into the beam pipe tubes of 1 m diameter, with their individual objectives regarding pumped species and needed temperatures. Also the open decision between cryocondensation at 3.7 K or physisorption on a sorbent at higher temperatures like 10 K for hydrogen pumping is discussed.
Besides the assessment of resulting thermal radiation on the mirror, the expected heat loads on the cryopumps, to be managed by the cryoplant of ET, are assessed.
Finally, the key parameter of frost formation on the cryogenic mirror, important for long operational phases without pause and maintenance, is derived from the predicted residual pressure of sticky gases like water.
This study presents a quantum dot (QD) fluorescence spectroscopy platform for full-temperature-range testing, based on a micro-machined Joule-Thomson (JT) cooler. Full-temperature-range testing is essential for evaluating QD fluorescence materials in different temperature applications, as temperature can affect their luminescence efficiency and spectrum. The study focuses on graphene QDs (initially attempted with pure anisole) and combines a Raman spectrometer with a low-temperature optical testing platform. The testing platform includes a small vacuum chamber with a JT cooling chip, whose evaporator section connects to a 1 cm² silicon wafer as a cold stage for optical testing. During the test, the sample's fluorescence intensity and spectrum are measured in the temperature range of 77K-473K. The paper details the design and construction of the system and verifies its testing performance for QD fluorescence spectra at different temperatures through experiments. The results show that the platform has excellent performance and reliability and can be widely applied in the research and application of QD fluorescence materials.
Since 2018, NASA and the National Institute for Occupational Safety and Health (NIOSH) have been developing a liquid oxygen storage module (LOXSM) based upon the NASA patent-pending cryogenic flux capacitor (CFC) technology. The LOXSM is aimed at potentially replacing the gaseous or chemical-based oxygen supply used in current closed-circuit escape respirators (CCERs)—devices that must be carried on the person, ready to be quickly deployed and used for escape in an emergency, particularly in underground mining applications—with the primary goal being to reduce the size of a CCER device compared to current devices. By virtue of the core CFC functionality, cryogenic oxygen stored within the LOXSM will be released in response to a heat input ideally from the breathing loop of the CCER. Prior efforts focused on the oxygen storage potential of silica aerogel materials that the CFC utilizes and have been previously reported. Work then continued to explore the LOXSM’s potential to retain the CO2 in the breathing air stream produced by the user when using the CCER. The work presented here describes the extensive test program for determining the CO2 retention potential of a LOXSM for use in a CCER, as well as the design evolution of LOXSM prototypes in response to the testing. The removal of CO2 from the breathing air stream by a gas to liquid phase change creates a synergy that may be exploited to reduce or eliminate the required chemical CO2 absorber material used in current CCERs. Testing has shown that it is indeed possible to completely remove CO2 out of an effluent stream at the flowrate required for the capacity of the CCER for an appreciable time, and that the LOXSM prototype design progression had a positive effect on that time.
Taconis oscillations represent spontaneous, usually unwanted excitation of acoustic modes in narrow tubes going from warm ambient environment into cold cryogenic space. These oscillations can drastically magnify heat leak and create vibrations undesirable for measurement instruments. In this study, modifications of classical constant-diameter tube are investigated. Specifically, variable-diameter tubes are found to have a profound effect on excitation, with wider tube segments in the warm environment strongly encouraging oscillations, while additions of properly chosen pipe network configurations can suppress the oscillations. The low-amplitude thermoacoustic theory, previously developed for thermoacoustic engines and refrigerators, is adapted for modelling Taconis phenomena, accounting for finite-length segments with temperature evolution where thermal-to-acoustic energy conversion takes place. Experiments are conducted with helium and hydrogen as working fluids to validate theoretical predictions. With the rapid development of liquid hydrogen storage and transfer systems, it is expected that Taconis oscillations may become an issue, and this study provides an initial modelling framework to assess this phenomenon in hydrogen systems.
The SPARC project at Commonwealth Fusion Systems (CFS) is a tokamak system designed to demonstrate commercially relevant fusion energy and achieve net fusion power output during the first operating campaign, with eventual pulse energies exceeding 1 GJ. The SPARC tokamak includes eight magnet systems, three of which utilize high temperature superconducting (HTS) tapes, cooled by the SPARC cryogenic system (CRYO) via three supercritical cryogenic loops at temperatures: {8 K, 15 K, 80 K}. CRYO 8 K and 15 K loops cool the HTS magnets to maintain thermal stability and prevent quench, while magnets cooled to 80 K are normally conductive. CRYO provides helium refrigeration from a hybrid cryogenic system including a steady-state cryoplant supporting all CRYO temperature loops, and a fixed volume 8 K blowdown system to remove heat and maintain temperature stability from the toroidal field (TF) magnets during and after fusion pulses. CRYO 4.5 K equivalent peak cooling power is 17 kW for the cryoplant and 2.9 MW for the blowdown system during a 10 second fusion pulse. Primary cryoplant mechanical equipment includes screw compressors, turboexpanders, heat exchangers, and circulation pumps while the blowdown system consists of a series of helium storage tanks operating at independent temperatures and pressures, with make up compressors to reset the blowdown system between pulses. CRYO also includes a distribution valve box and multiple vacuum jacketed process lines ranging in nominal diameter from 20 - 600 mm. This paper investigates the various sub-elements which in combination represent SPARC CRYO and attempts to address some of the technical challenges identified by the team.
Acknowledgement
Work supported by Commonwealth Fusion Systems.
The Proton Improvement Plan-II (PIP-II) is a major upgrade to the Fermilab accelerator complex, featuring a new 800-MeV Superconducting Radio-Frequency (SRF) linear accelerator (LINAC) powering the accelerator complex to provide the world’s most intense high-energy neutrino beam. The PIP-II Linac consists of 23 SRF cryomodules operating at 2K, 5K, and 40K temperature levels supplied by a single helium cryoplant providing 2.5 kW of cooling capacity at 2.0 K. The PIP-II cryogenic system consists of two major systems: a helium cryogenic plant and cryogenic distribution system. The cryogenic plant includes a refrigerator cold box, a warm compressor system, and helium storage, recovery, and purification systems. The cryogenic distribution system includes a distribution box, intermediate transfer line, and a tunnel transfer line consisting of modular bayonet cans which feed the cryomodules. A turnaround can is located at the end of the Linac to turnaround cryogenic flows. This paper describes the layout, design, and current status of the PIP-II cryogenic system.
MYRRHA at SCK CEN in Mol/Belgium will be the world’s first large-scale Accelerator Driven System (ADS) at power levels scalable to industrial systems for unparalleled research opportunities in spent nuclear fuel, nuclear medicine, and fundamental and applied physics. MYRRHA was approved by the Belgian government in 2018, releasing the funding for a first phase of staged implementation and operation. MINERVA, the implementation of phase 1 of MYRRHA, covers the design, construction and commissioning of the first Linac section up to 100 MeV, a Proton Target Facility (PTF) and a Full Power Facility (FPF). It is scheduled to start beam operation in 2027. Phase 1 also comprises R&D and pre-licensing towards the MYRRHA sub critical reactor driven by a 600 MeV proton beam.
The MINERVA proton linac will accommodate 30 identical cryomodules to boost the beam energy delivered by the normal-conducting frontend from 16.6 MeV to 100 MeV. Each cryomodule will contain two superconducing RF single-spoke cavities immersed in a superfluid Helium bath at 2 K. The design and architecture of the overall cryogenic system is derived from the stringent reliability requirements imposed by the future reactor.
We present the design, architecture, and development status of the MINERVA cryomodules and associated cryogenic system towards the implementation phase of the project, as currently defined in collaboration with the collaboration partners at IJClab, ACS, and CEA/DSBT. Additionally, we summarize the preliminary results of cryogenic and RF tests for the prototype MINERVA cryomodule, while these activities are ongoing at the site of SCK CEN’s collaboration partner IJClab.
Funding source: This work is supported by the MYRRHA programme at SCK CEN (Belgium).
The cryogenic plant operating 10+ years at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory (BNL) and supplying the liquid Helium for three superconducting Radio Frequency cavities. The objective is the continuous Helium supply without interrupting operation. This paper outlines our experience in troubleshooting of various failures of the cryogenic plant and main considerations regarding the selection of the equipment and components.
Air Liquide Advanced Technologies is pleased to share the results and lessons learnt through the start-up of SLAC 2K cryogenic module. 2K temperature is reached by pumping down the accelerator cavities filled with liquid helium to subatmospheric pressure. In order to pump the cavities down to 30 mbara, a train of 5 high speed cold compressors on magnetic bearings is used. Magnetic bearings allow for resilient operation of the cold compressors with changing operating conditions in terms of pressure, temperature and rotating speed.
The tuning of the cold compressor speeds throughout the pump-down is key to reach stable operation at 2K, so as to maintain all 5 compressors within their nominal operating range. In particular, stabilizing the pressure at the end of the pump-down, while liquid helium in the cavities enters superfluid state and gaseous density becomes very low, can prove challenging. Air Liquide Advanced Technologies will present the final “pump-down path” established for SLAC, and how the tuning was performed, allowing for a reproducible, reliable and fast pump-down on SLAC cryogenic installation. Test results showing the assessment of the minimum and maximum operating flow at 2K will also be presented.
Helium cryogenic systems operating below the normal boiling point (of 4.22 K) are required for many modern high-energy particle accelerators to achieve the necessary performance criteria. Temperatures below the normal boiling point are established by lowering saturation pressure below atmospheric conditions using vacuum equipment. FRIB operates a multi-stage string of cryogenic compressors (or “cold-compressors”) to achieve the sub-atmospheric pressures required for the accelerator operating conditions of approximately 2 K (30 mbar). Housed within a vacuum insulated vessel (i.e., the sub-atmospheric cold box), the cold-compressor system re-pressurizes the helium from approximately 30 mbar to above atmospheric conditions before injecting the flow back into the helium refrigerator. Despite the implementation of cold-compressors in several existing large-scale cryogenic systems, openly available research literature is insufficient to provide the information necessary for a general characterization of the performance and stability for these cold compressors. To address this deficiency, this present study provides such a characterization through a modification of a centrifugal compressor performance prediction code previously developed by the authors. This code enables performance prediction by using optimally selected enthalpy loss correlations and basic impeller and diffuser geometrical data. Using this code and extensive test data previously collected for the FRIB cold compressors, the performance of these compressors is characterized, permitting a reliable performance prediction. This is anticipated to allow assessment and prediction of optimal operational envelops that ensure stable and efficient operation.
Quantitative bending strain property of critical current is inevitable for designing spiral and pancake coils in practical magnets and other SC applications. The present study is to establish a quantitative measuring method on the bending strain dependence of Ic for REBCO tapes. Practical tapes have two types of twinned structure. They are characterized as having <100> and <110> orientations along the tape axis. These composite tapes consist of brittle oxide and several metallic components which give asymmetrical piling structure. So the bending strain behaviors are characterized in several aspects of structure and applied bending direction. When bending the tapes towards edgewise direction, the bending strain distributes within almost whole cross-section from the maximum tensile strain to compressive one through the neutral strain axis. Decreasing bending diameter, the tape fractures at a critical bending strain. In the case of flatwise bending, there are two kinds of bending manner for a very thin SC layer. In order to measure a compressive bending strain, the tape is bent inwards the neutral axis. For realizing the tensile bending state, the tape is bent outwards the neutral axis. The degradation bending diameter limit (D95) at which the critical current begins to degrade was ~ 7 mm by both compressive and tensile flatwise bending and ~400 mm by edgewise one for REBCO tapes examined here. The degradation (fracture) behavior is different for either case of compressive and tensile bending mode. The tensile bending fracture initiates at a interface of SC layer, while the compressive bending fracture happens by buckling or 45o shearing.
So far, the round-robin-test has been proposed and successfully performed to establish the standard of the test method for measuring the mechanical properties and the critical current of superconducting properties of various composite superconducting wires, and has contributed significantly to the establishment of international standards (IS). With the development of high-performance HTS wires and their applications to coils/magnets, establishing standard methods for evaluating their electromechanical properties (EMPs) at cryogenic temperatures has become important. This time, an international round-robin test was promoted to establish a test method for the electromechanical properties of HTS composite wires at liquid nitrogen temperature. Tensile tests were performed to measure the critical current based on the stress intervals at cryogenic temperatures for three REBCO tapes and one kind of BSCCO tape. Samples were distributed to 6 participating laboratories in 5 countries for testing according to specified guidelines. Test results delivered from all participants were evaluated using statistical tools to investigate the main causes of scattering in the test results and their magnitude. The EMPs assessed were critical current (Ic), reversible stress limit (Rrev), and retention stress limit (Rret), which were determined through a stress-based test method. The Ic measurements were conducted using broad and narrow stress intervals, and reversible and retention stress limits were defined based on specific 99% Ic0 recovery and 95% Ic0 retention criteria. The objectives of RRT are to establish an IEC standard for a testing method of the electro-mechanical properties of HTS wires, including REBCO, under uniaxial tension. The RRT results for the electro-mechanical property test of HTS wires under tension at liquid nitrogen temperature are presented and discussed.
Acknowledgments: This work was supported by KEIT grant funded by the Korean government (MOTIE) (Grant No. 20020421). It was partially supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2022M3I9A1076881).
Bi-2212, a promising cuprate High Temperature Superconductor (HTS), is the only one capable of being formed into round wires. It has a high upper critical magnetic field and critical current density, making it an ideal choice for use in the Cable-In-Conduit Conductors (CICC) of the China Fusion Engineering Test Reactor (CFETR)'s Central Solenoid coils. The Over-Pressure (OP) heat-treatment can dramatically improve the multifilamentary Bi-2212/Ag wires critical current density, however, this also leads to a decrease in diameter and an increase in void fraction in the CICC cables, which can jeopardize magnet stability. To remedy this, a pre-Over Pressure (pre-OP) heat-treatment procedure has been implemented to reduce wire diameter before cabling. By analyzing the wire's critical current performance under axial stress, inter-wire contact force, and bending stress through various tests and simulations, the axial strain and cross angle effects on the pre-OP reacted Bi-2212/Ag wires' critical current degradation have been studied, thus providing guidelines for manufacturing optimal Bi-2212/Ag CICCs.
BSCCO and REBCO tapes have a rectangular cross section, making them suitable for coil applications and power transmission cables. In short, the advantage is that it is easy to bend, but strain due to bending is inevitable. and in BSCCO there is a difference in strength between the two. Compression test results with a bending jig showed that it was more susceptible to compressive strain than tensile strain.
To understand these behaviors, compressive strain tests and bending tests were conducted. Specifically, critical current measurements were made while performing compression tests using a curved beam called a Spring Board and bending tests using cylinders with multiple diameters. In BSCCO tapes, where the filament geometry is complex, it is difficult to visualize the compression fracture. Therefore, we also performed diffraction experiments using synchrotron radiation with high-brilliance X-rays, which can evaluate internal bending strain nondestructively.
We want to show that by understanding the strength on the compression side, we can relate the degradation due to compressive strain from bending.
Nb$_3$Sn magnet conductors will continue to be the workhorse material for accelerator magnets over the coming decade because they can deliver significantly higher magnetic fields than Nb-Ti at significantly lower cost than higher performance HTS conductors. While R&D enhancements for advanced Nb$_3$Sn could improve performance by 30% or more in the 15-16 T field range envisioned for future dipoles, pushing the limits of the present restacked rod process (RRP®) conductors provides a competitive baseline to emulate. Developments in cabled REBCO tape HTS conductors and Bi-2212 round-wire strand are creating opportunities for hybrid Nb$_3$Sn-HTS dipole magnets approaching 20 T and solenoid magnets pushing toward 50 T. Bi-2212 conductors must confront a still nascent supply chain with small production batches and high cost due to factors not related to materials or production, where help will come from efforts to commercialize new ultra-high field laboratory magnets. REBCO cables are under study from multiple agendas, but testing activities at NHMFL and elsewhere reveal that run-to-run and along-run property variations are still rather wide. Conductors are not yet interchangeable across manufacturers for cables in the accelerator sector and for winding solenoids. The present billion-dollar investment in REBCO-based fusion could spur a new era of helium-free magnet development, creating potential challenges for the accelerator sector to find synergy between helium and helium-free technology development ecosystems. Actions are proposed to extend the benefits of private investments to the accelerator sector.
The record Jc of commercial Nb3Sn conductors has been at a plateau since the early 2000s; however, much higher Jc than the state of the art is required for building the high-field accelerator magnets in future energy-frontier circular colliders. In the past few years a new type of Nb3Sn conductor with artificial pinning centers (APC) based on the internal oxidation method has demonstrated significantly superior performance relative to the state of the art. In 2019 the APC conductors we developed first reached the non-Cu Jc specification required by the 16 T dipole magnets for the proposed Future Circular Collider (FCC)-hh. Since then our efforts have been mainly focused on pushing the APC strands toward readiness for practical applications, and great progress has been made. It was also found that this method not only significantly improves non-Cu Jc at high fields (e.g., above 10 T), but also dramatically reduces persistent-current magnetization at low fields (e.g., below 3 T) relative to the restacked-rod-process (RRP®) conductors due to the point pinning behavior. In this talk the opportunities, challenges, current status and future plans for the APC Nb3Sn conductors will be discussed.
Recent years have seen significant development of superconducting Bi-2212 wires and magnets in the US with record critical current density, record wire lengths and record performance model magnets. For accelerator magnets, Rutherford cables have been used to construct racetrack coils, common coil dipole, and a canted cosine theta dipole magnet with structural management ability and good field quality. In this talk, we discuss design, fabrication and performance of Bi-2212 wires, their heat treatments, and performance in solenoids. We also discuss fabrication and characteristics of Bi-2212 Rutherford cable, its readiness for accelerator magnet development, the prototyping efforts of building high-performance canted-cosine-theta Bi-2212 magnets, technology gaps (wires, cables, and magnets) that stand in the way of a fully competitive Bi-2212 magnet technology, and ongoing work that address these gaps.
This work is supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under the framework of the U.S. Magnet Development Program. NHMFL is also supported by the National Science Foundation and the state of Florida. Bruker OST and Engi-mat LLC are supported by the US DOE, OHEP with SBIR awards.
Cryo-Electric planes are being envisaged for the 2030’s. A key technological hurdle for realizing this is the availability of flight-weight motors, generators, and power distribution systems. Historically superconducting industrial and marine machines have been demonstrated – but not at the required flight power and volume densities. Developments for compact lightweight highly efficient rotating machines for aircraft applications are now being conducted worldwide using both government and private resources. NASA has identified the need for motors rated 3 MW @4500 rpm and generators 22 MW @6500 rpm [1]. Both conventional and superconducting options are under consideration. NASA and ARPA-E are funding several programs in the USA. Likewise, Europe, New Zealand, Japan, Korea, and other countries are funding similar programs.
This talk provides an overview of the key historic cryogenic machine demonstrations and show the missing performance space to meet aerospace application. A motor rated 3 MW, 4500 RPM is used here for reviewing various technologies. Both conventional coils cooled to cryogenic temperature and superconducting coils are included in the review. The status of some of the programs is presented. To achieve machines with > TRL-6 in the next 5-6 years will require concentrated focus in areas such as AC loss estimates for superconductor and high- conductivity aluminum windings, on-shaft high-speed coolers for cooling the rotating mass, power sources for energizing coils on rotor wirelessly, compact lightweight refrigerators, and high voltage (~1000 V) electric drives. Irrespective of selected thermal sinks, it would be essential to employ a link gas (such as GHe) for cooling the coils, and any discussion of the efficiency per say becomes irrelevant. Also, cooling with GHe has limitations imposed by its working temperature, pressure, mass flow, etc. The size of the coils will, therefore, be determined by these limitations. For example, if LH2 is used as a thermal sink, it would be necessary to condition the GHe to temperatures suitable for coils. Likewise, if LNG is assumed as the thermal sink, it would be necessary to employ refrigerators for lowering temperature of the link GHe to suit the superconducting coils.
To achieve the goal of TRL-6 or higher for motors and generators soon, government support commitments are necessary, like those of Air New Zealand’s Mission Next Gen Aircraft -2030.
Electrified aircraft are being developed to address climate change by reducing the fuel burn and emissions of aircraft. The large majority of aviation’s impact on the environment is caused by large transport aircraft, or those that can carry about 150+ passengers. At this scale, MW-class electrified propulsion systems are required. To achieve a net fuel burn and/or emissions benefit after adding the mass of this extra system to the aircraft, the performance of the electrified propulsion components must exceed the state of the art. Not only must the specific power of electric machines improve to limit the mass of the system, but their efficiency must also improve to limit waste heat (which necessitates added mass for a thermal management system) and limit oversizing other electrified propulsion components (which must overcome the machines’ inefficiency). In numerous cases, the efficiency of electric machines has a stronger influence on the aircraft than their specific power. Superconducting and cryogenic machines typically can achieve higher efficiency than their counterparts that operate above ambient temperature. The paper will describe the motivation for superconducting and cryogenic electric machines (as opposed to machines operating above ambient temperature), including references to system-level aircraft studies, studies comparing superconducting/cryogenic machines to conventional ones, and state-of-the-art electric machines for aeronautics applications.
NASA’s high efficiency megawatt motor (HEMM) is a partially superconducting, 1.4 MW electric machine designed for electrified aircraft propulsion. HEMM’s high performance is enabled by a superconducting rotor composed of 2nd generation high temperature superconducting (HTS) coils that are designed to operate at temperatures below 62 K. The superconducting rotor is conductively cooled to cryogenic temperatures using a rotating cryocooler embedded inside the machine’s shaft. The development of HEMM’s electromagnetic design has been supported by testing of sub-scale and full-scale superconducting coils in liquid nitrogen (LN2). This experimental work has been previously published by the authors. Although these LN2 tests have reduced multiple risks in HEMM’s design, the HTS coils were not operated at their designed thermo-electro-magnetic operating condition. This paper presents the first test of HEMM where the HTS coils were conductively cooled to their rated operating temperature and then excited at their rated operating current and magnetic field.
The experimental setup consisted of HEMM’s full-scale superconducting rotor in a cryogenic vacuum chamber. The temperature of both the thermal interface to HEMM’s cryocooler and the structural interface to HEMM’s shaft (and cryocooler housing) were accurately controlled. To limit the complexity and cost of the test, only three of the rotor’s twelve HTS coils were included. These three coils were installed on adjacent rotor teeth to ensure the magnetic field excitation on the central coil was representative of HEMM; this claim will be supported in the paper by reporting thermal and electromagnetic 3D finite element analyses (FEA) of HEMM and the experiment.
The paper will present measurements of the rotor’s temperature distribution during the cool down from room temperature along with a comparison to 3D FEA of HEMM. This discussion will emphasize the duration of the cool down as well as the temperature gradient across bolted interfaces and other mechanical contacts. Thermal and electrical measurements will be presented for operation at different direct current excitations up to the rated current of the rotor. The paper will include a discussion of the ability of HEMM’s design to sufficiently cool the rotor and stably operate the superconducting coils at their rated direct current under conductive cooling with a cryocooler.
By: Olivia BRUJ1, Milan MAJOROS2, Michael SUMPTION3 and C.G. CANTEMIR4
Affiliation:
1) National Institute for Research and Development of Isotopic and Molecular Technologies of Romania, email: olivia.bruj@itim-cj.ro
2) Ohio State University, email: milan.majoros.2@gmail.com
3) Ohio State University, email: Sumption.3@osu.edu
4) CGC Ultramarin Ltd, email: CGC.ultramarin@gmail.com
Abstract
This paper presents some aspects of the implementation of superconducting coils in megawatt size electric machines designed to maximize the power density as a main optimization criterion. Such electric machines will be suitable for electric flight and alike and / or hybridization of big jet engines, albeit the technology may be applied to almost any other category of electric machines due a very cost effective fabrication technology mated with a minimal usage of materials.
Generally speaking, increasing the supply frequency of an electric machine is very helpful to decrease its weight and size, however increasing the frequency produces two parasitic effects known as the “Skin Effect” and the “Proximity Effect”. The combined effect of such losses is an important fraction of the total AC losses, around 80-90% of the practical implementations considered herein. For a given magnet wire (current carrier) the intensity of these two effects is proportional to the frequency, however these effects are also dependent to the general size, the specific geometry of the current carrier and the resistivity of the material (among other specific implementation aspects). As a general rule, large conductor sizes are highly affected (negatively) by these two effects. This is the main reason why high frequency currents are used mainly for small size electric machines, while large size electric machines cannot take full advantage of a high frequency supply source. Particularly, superconductivity is highly benefic for decreasing DC losses, however the AC losses will worsen.
The present work presents a specific geometry of the superconductor current carriers, herein named Tuned Winding. This geometry is able to highly decrease the skin and the proximity effects while taking full advantage of the highly increase electric conductivity. A simple computation algorithm (also presented) enables the determination of an optimum geometry for each particular application, including full practicability for Megawatt class electric machines. Basically the expression of the AC resistance is non-linear and therefore the computations are based on the Nonlinear Conjugate Gradient (NCG) method which proved to be highly adequate. The NCG method is a prominent algorithm for the numerical optimization of nonlinear problems with low memory requirements. Furthermore, certain technologic implementations for Megawatt class electric machines are also presented including the simulation of their thermal behavior operating with cryogenic coolants.
Abstract - The increasing demand for high-power density electric motors in transportation industries opens a new research opportunity to develop motor topologies with less weight and higher efficiency. In particular, electric aircraft applications require very high power density motors. And increases of efficiency are desired for transportation, to reduce system impacts of high heat loads and reduce fuel costs; e.g. yearly savings of $4B for aviation fuel worldwide could be realized, for a 1% increase of drivetrain efficiency. Flux-switching machines are used by a large percentage of the automotive industry, since they have reasonable power and efficiency for a wide range of motor speeds from low to high. And axial flux machines are commercially available for the electric aircraft industry, e.g. by MagniX for Eviation aircraft.
This paper provides the design of a new 1 MW 20-pole/15-slot radial flux switching machine with double rotors, and using high-temperature superconductor tapes for the field coils and a cryofuel thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is chosen for the armature conductors operating at 25-50 K, and Y-Ba-Cu-O high-temperature superconducting tapes are used for the field coils operating at 20-25 K. Flux switching motors provide an interesting opportunity to incorporate superconducting tapes for the DC field coils, since the field coils are stationary which are relatively straightforward to cool. However there is some risk for the field coils, since AC and harmonic B-fields will penetrate into the field coils to some degree. However solutions to address the problems of AC penetration were discovered and will be presented.
The active part power density including rotors, armature windings and field coils obtained with the proposed design is > 100 kW/kg. The efficiency can be higher than 99% which is a significant increase from 94-96% of motors operating at ambient temperatures, to greatly reduce heat loads and reduce fuel and operating costs.
Acknowledgements. ARPA-E Contract # DE-AR0001355 and Subaward # 89703021SAR00022, AFOSR LRIR #18RQCOR100, and the AFRL/RQ Aerospace Systems Directorate
There is growing interest to use superconductors for actuator applications. High-field superconducting electromagnets enable a much higher performance. DC-excited stator coils in such systems are subjected to time-varying magnetic fields of up to several hundred mT, leading to significant AC loss. Inherently stable no-insulation coils make motion systems more reliable, but come at the cost of even higher AC loss. Here we focuss on the AV loss in such NI ReBCO coils, determining them both numerically and experimentally.
We developed a specific test arrangement and measured the AC loss in 200 mm long and 20 mm wide NI ReBCO racetrack coils made of single 4 mm wide tape conductor at 4.2 and 77 K. The combined effect of a parallel AC magnetic field with an amplitude of up to 100 mT and a DC transport current up to 600 A was investigated. The loss was measured simultaneously with magnetic, electric and calorimetric methods. The results largely confirm the numerical model predictions, which were obtained a-priori from only the coil dimensions, its critical current and the effective time constant τ associated with radial current redistribution. For this research, the coils were solder-impregnated resulting in a relatively low turn-to-turn surface resistance of 1 μΩ∙cm^2 and a τ-value of approximately 65 s, corresponding to a characteristic frequency f_c of 2.4 mHz.
The AC loss of the coils is determined in the frequency range of 0.5 mHz to 1.25 Hz. For f<f_c, coupling currents dissipate homogeneously throughout the winding pack. Whereas for f>f_c, the effect of current concentration due to the skin-effect (P_ac∝√f) that is predicted by the model is also clearly visible in the data. A DC transport current in the coils further increases the AC loss as the induced currents cause a displacement of the transport current in the superconductor. Experiments at 4.2 K and at 77 K confirmed that the dominant loss contribution being the coupling loss can be readily predicted from the value of the time constant τ, which can be straightforwardly measured with a fast current discharge test.
Despite the inherent thermal stability of NI ReBCO coils, the significantly higher AC loss compared to insulated coils makes this technology a less viable option for high-dynamic applications such as the magnetic field coils in a linear motor system. However, an application-specific optimization of the turn-to-turn resistance, seeking a smart compromise between coil operational robustness and acceptable thermal budget, can make such coils a feasible option for high-dynamic motion systems.
In the pantheon of topological materials, Weyl semimetals have been a persistent focus due to the predictions of interesting anomalous effects such as the chiral anomaly, the Nieh-Yan anomaly, and axion electrodynamics, that are normally expected to be found in the realm of high-energy physics rather than condensed matter physics. Nonetheless, while theoretically feasible, the observation of these effects in Weyl semimetals often is quite difficult due to the presence of many trivial band excitations at the same energy as the topological excitations. Recent work has shown that the topological aspects of Weyl semimetals may be distilled from the overall excitations of the system via the realization that the relevant Weyl physics has another high-energy parallel to systems connected to a distorted spacetime metric referred to as pseudogravity. In this talk, I will discuss how pseudogravity naturally emerges in Weyl semimetals and address some of the open problems associated with the pseudogravitational interpretation of Weyl semimetals with a focus on understanding recent experimental results.
We propose Berry phase enforced spinor superconducting orders arising from pairing topological Fermi surfaces with their Chern numbers differing by an odd integer. This exotic pairing structure can exhibit a single pairing gap node on a Fermi surface and is described by monopole harmonics with half-integer charge and fractionalized half-integer partial-wave symmetry. We investigate topologically protected surface states in the simplest example of spinor pairing with pair monopole charge -1/2 when spineless fermions in a topological trivial Fermi surface pair with spin-1/2 electrons in a helical Fermi surface with Chern number -1 under hard-core interaction between them. We find exotic surface states protected by the topological spinor superconducting order.
This talk will survey recent theoretical and experimental works on intrinsic nonreciprocity of quantum materials, as manifested by direction-dependent electrical resistivity. I will highlight two types of colossal nonreciprocal transport phenomena: (1). nonlinear Hall effect leading to divergent nonreciprocity in transverse resistance; (2) superconducting diode effect leading to 100% nonreciprocity in longitudinal resistance. Applications of nonreciprocal quantum materials in terahertz electronics, energy harvesting and cryogenic computing will be discussed.
The National Ignition Facility (NIF) houses the world’s most energetic laser which can deliver over 2MJ of energy at the 500TW level of power of 351nm UV light. This immense optical energy is focused on a small ‘target’ that can create such high energy densities that the unique physics underlying this extreme regime can be explored. One of the primary goals of the NIF has been to explore controlled nuclear fusion where the energy from the laser is used to compress hydrogen (specifically, its isotopes deuterium and tritium or DT) to about 100 billion atmospheres at which point temperatures reach about 100 million Kelvin, conditions where the atoms can overcome Coulombic repulsion and fuse. This grand challenge of ignition where the nuclear fusion energy out was greater than the optical energy in was successfully achieved on December 5, 2022 in a landmark experiment. This is expected to usher in a new age of nuclear fusion research with diverse and far-reaching goals.
Of the many, one of the challenges of this experiment is the formation of a hollow spherical ice layer off the DT fuel at ~19K with extremely high dimensional precision. In this presentation, we will start with a brief overview of the key aspects of the complex and multifaceted system needed to carry out these experiments. We will then focus on the design and engineering done to fabricate targets which can reproducibly meet these stringent sub-milli Kelvin thermal control requirements. We will also discuss the technique used to make and characterize the exquisite smooth and uniform hydrogen ice crystal formed by transporting the fuel using a fill-tube with an inner diameter of 1μm.
NIF and Photon Science (llnl.gov)
https://www.cec-icmc.org/2023/awards/
There are two 450W and one 890W helium cryogenic systems, which were installed at Taiwan light source (TLS) and Taiwan photon source (TPS), respectively. The TLS helium cryogenic system were used for one SRF cavity and five superconducting magnets. The TPS helium cryogenic system was used for two SRF cavities at the present stage. These three helium cryogenic system experienced the pressure degradation, which reduced the performance and increased liquid nitrogen consumption for the precooling over the past few years. We had try to set up the cryogenic adsorber to capture the impurities, but, making no difference for the pressure degradation to the system. The impurities comprised of not only gas but also moisture. It was found that the cryogenic adsorber was not efficiently for the moisture. This paper was aimed to study the phenomena of pressure degradation. The moisture removal system was also presented and discussed.
As hydrogen continues to gain momentum as a clean fuel and energy carrier in industrial sectors, hydrogen liquefaction has emerged as an essential part of the supply chain to reduce transportation and storage costs. Hydrogen has historically been produced from electrolysis and steam-methane-reforming, but as the market continues to grow, biproduct hydrogen from chemical processing and biomass reforming has become more prevalent. These processes result in the production of hydrogen feed gas with a broad range of impurities. Additionally, the development of novel liquefaction cycles which optimize performance and efficiency operate under different process conditions than traditional liquefiers. These factors have created a need for additional experimental data on molecular sieve materials. These materials are crucial for the cryogenic purification portion of a hydrogen liquefier to prevent impurities from freezing out during liquefaction, creating blockages which disrupt operations. This work presents a new experimental system that has been developed to study cryogenic purification materials over a broad range of cryogenic temperatures and impurity levels. Results of common molecular sieve materials are presented.
In this paper, reliability analysis of a large-scale helium cryogenic refrigeration system with cooling capacity of 2500W@4.5K/500W@2K is studied. Reliability model and failure rate of the refrigeration system based on fault tree is developed. It consists of liquid helium and superfluid helium subsystems. The key components include two helium screw compressors, six gas bearing expansion turbines, eight cryogenic heat exchangers, three cold compressors, six room temperature dry vacuum pumps, three subcooling helium heat exchangers and cryogenic adjusting valves, etc. Combine with the failure rate of similar equipment in our laboratory, and the public database, fault tree of insufficient cooling capacity as top event of liquid helium and superfluid helium subsystems is analyzed in details. By improving the reliability of helium screw compressors and expansion turbines, Mean Time to Failure (MTTF) is optimized to 9360 h, larger than our design target 8000h. In our experiments, it operates more than 2000 hours and hundreds of start-stop sequences, which verifies our theoretical failure data of such key components. Through this work, the failure rate database of this large-scale helium cryogenic refrigeration system is established, which will support the design and development of similar machines in the near future.
At the European Spallation source (ESS), 2 GeV proton beams with a power of 5 MW are injected on a rotating tungsten target wheel with a repetition of 14 Hz and a pulse length of 2.86 ms to produce high energy spallation neutrons. The high-energy neutrons are slowed down to cold and thermal energies by the moderators, which consists of a thermal water pre-moderator and two liquid hydrogen cold moderators, all optimized to achieve a high cold neutron brightness. The two hydrogen moderators are located above the target wheel and the nuclear heating is estimated to be 6.7 kW for the 5-MW proton beam power. The current plan is to replace them with four (two above and two below the target wheel, respectively) in the future. The nuclear heating for the four moderators is calculated to be 17.2 kW. A large-scale 20 K helium refrigeration system, which is called Target Moderator CryoPlant (TMCP), has a cooling capacity of 30.2 kW at 15 K. A 385 m-long cryogenic transfer line (CTL) and a valve box have been installed in summer 2022, because all the ESS helium cryoplants are co-located in order to facilitate maintenance and consolidate utilities. The purpose of it is to cool the cryogenic moderator system (CMS) that provides subcooled liquid hydrogen with a temperature of 17.5 K to the hydrogen moderators and remove the nuclear heating generated at the moderators. When the proton beams are injected or tripped, the enormous heat load is suddenly changed. The available cooling capacity has to be changed by adjusting the feed helium flow rate in order to maintain the hydrogen temperature to the moderator at 17.5 K within temperature fluctuation of ≤0.1 K. The valve box has functions to adjust the feed flow rate, the supply temperature to the CMS and the return temperature to the TMCP cold box without changing the cooling capacity of the TMCP cold box. In this study, we investigated the stability of the TMCP operation when the heat loads of 5.92 kW and 17.5 kW for the two- and four-moderator arrangements were rapidly applied and how to mitigate the propagation of the temperature fluctuation in order not to affect the CMS supply temperature. For the transient heat load of 5.92 kW, the fluctuation of the CMS supply tempeature was able to be mitigated by only a PID control of the return temperature within the allowable one of 0.4 K. The result indicates that for 17.5 kW, the combination of the PID and the feedforward control is essential to mitigate not only the CMS supply temperature within 0.1 K but also the pressure fluctuation.
Cryogenic compressed hydrogen is one of the most possible hydrogen storage methods to achieve a high storage density, which can meet the long-distance driving demand of hydrogen fuel cell vehicles. In the process of transportation, the precooling process of cryogenic compressed hydrogen is very important. This precooling process requires a continuous refrigeration power from ambient temperature down to a low temperature in the range 30–100 K. It is usually cooled with a single-stage refrigerator, especially when the temperature is above about 50 K. There is a significant loss during the precooling, because the sensible heat of H2 is distributed all around the temperature range and refrigeration is fixed at the cold-end temperature. In this case, the efficiency is relatively low. In this paper, we will show a method of applying the temperature-distributed refrigeration power on the regenerative refrigeration. Such a temperature-distributed refrigeration relies on real gas effects of the working fluid. The pure N2 with an average pressure of larger than 4 (reduced pressure) generates the temperature-distributed refrigeration power between about 75 K and above 200 K, which decreases the heat loss of precooling significantly. The precooling efficiency of the cryogenic compressed hydrogen is able to achieve more than two times larger than that cooling with only the fixed cold-end temperature in some specific range.
This paper describes the development of 2 kW class reverse-Brayton refrigeration system. The refrigeration cycle is designed to have cooling capacity of 2 kW at 77 K, with operating pressure of 0.5 and 1.0 MPa at low and high pressure side. Neon gas is adopted as a working fluid. The system is consist of scroll compressor package, plate heat exchangers and turbo expander. Especially, several helium scroll compressors, which are originally used for driving GM cryocooler, are packaged to produce the system pressure and flow rate. Three segments of plate heat exchanger are adopted cover wide temperature range and the refrigeration power is produced by turbo expander. The developed refrigeration system is successfully operated at wide temperature range including its target temperature. In experiments, all parameters such as pressure, temperature, mass flow rate and valve opening are measured during cool-down process and steady state. Cooling capacity is measured with heat load by electric heater. The developed refrigeration system shows cooling capacity of 1.83 ~ 2.78 kW at 68 ~ 102 K of cold-end temperature range.
ABSTRACT: An 18 kW@4.5 K & 4 kW@2 K helium refrigerator is being developed in China by the Technical Institute of Physics and Chemistry, CAS. This large-scale helium refrigerator provides different cooling capacity at the 50-75 K, 4.5-75 K and 2 K levels. This helium refrigerator works based on Claude cycle refrigeration process, which uses 5 sets of turbines (10 turbines totally) to bring the temperature down to 4.5 K. Four cold compressors are arranged in series to pump gaseous helium from atmospheric pressure to 0.03 bar in order to decrease the temperature of 2 K helium bath from 4.5 K down to 2 K. A set of subatmospheric pressure compressors is used to compress subatmospheric helium gas downstream from cold compressors to medium pressure 4.05 bar and is connected directly to high pressure compressors. This paper provides an overview on the process design, system design and preliminary component design results in the development of this 18 kW@4.5 K & 4 kW@2 K helium refrigerator.
KEYWORDS: Large-scale helium refrigerator, Superfluid helium refrigerator, Process flow diagram, Cold box
At the ESS target, high energy spallation neutrons are produced by impinging 5 MW proton beam on the high-Z material, tungsten. The proton beam is pulsed with a repetition of 14 Hz and a pulse length of 2.86 ms. The spallation neutrons are moderated to cold and thermal energies by the moderators. The moderator system consists of a thermal water pre-moderator and two liquid hydrogen cold moderators, all optimized to achieve a high cold neutron brightness. The nuclear heating is estimated to be 6.7 kW for the 5-MW proton beam power. A cryogenic moderator system (CMS) has been designed to continuously supply subcooled liquid hydrogen with a temperature of 17 K and a parahydrogen fraction of more than 99.5% to the two moderators. The heat load will be removed via a heat exchanger in the CMS cold box by a large-scale 20 K helium refrigeration system called the Target Moderator Cryoplant (TMCP) with a cooling capacity of 30.3 kW at 15 K. A temperature controller regulates the supply temperature of the TMCP cold box by acting two bypass valves for the two cold parallel turbines. The high-pressure helium stream with the temperature of 15 K is delivered to the CMS cold box through a 385-m long vacuum insulated cryogenic transfer line (CTL) and a valve box, which has functions to adjust the feed flow rate and the supply temperature to the CMS and the return temperature to the TMCP cold box. The first commissioning of the TMCP without the CTL and the valve box has been finished in 2019. The installation of the long CTLs and the valve box has been completed in summer 2022. Subsequently, the second commissioning of the overall TMCP has been performed without connecting to the CMS cold box until December 2022. The final installation of the connection between the valve box and the CMS cold box is planned for 2023. In this study, the TMCP cooldown and warm-up processes have been studied based on the simulation results for the CMS cooldown and warm-up operation conducted by the authors in advance. It turned out that the TMCP has to operate the two cold parallel turbines to achieve the required CMS cooldown operation because most of the cooling capacity was consumed to cool the long CTL. In the warm-up process, the supply temperature was successfully increased to 30 K at the desired warm-up speed, controlling the cooling capacity of the TMCP where one warm turbine and one cold one were operated. The TMCP operational procedures for the cooldown and warm-up have been established and its operational parameters have been optimized.
Development of a Portable Stand-Alone 20 K Brayton Cycle Helium Refrigeration System
W.F. Reaves1, A.M. Swanger2, R.A. Gordie3, J.D. Taylor1
1Bionetics LASSO, Kennedy Space Center, Cryogenics Test laboratory, KSC, FL 32899 USA
2NASA Kennedy Space Center, Cryogenics Test Laboratory, KSC, FL 32899 USA
3Jacobs TOSC, Kennedy Space Center, Cryogenics Test laboratory, KSC, FL 32899 USA
From 2012 to 2015, NASA funded development of the Ground Operations Demonstration Unit for Liquid Hydrogen (GODU-LH2) at Kennedy Space Center that scaled up and matured Integrated Refrigeration and Storage (IRAS) technology. IRAS involves the integration of an external helium refrigeration system with a cryogenic storage tank via an internal heat exchanger, and allows advanced operations such as zero boiloff and densification of the liquid. The refrigeration system employed for GODU-LH2 was a Linde LR1620 piston-Brayton cycle machine with an RSX helium compressor. Rated capacities for the LR1620/RSX are 390 W at 20 K without liquid nitrogen (LN2) precooling, and 880 W with precooling; actual performance of the GODU-LH2 unit was 883 W and 466 W with and without precooling respectively. The GODU-LH2 system was broken up into two separate shipping containers—one housing the cold-box, compressor, and gas management hardware, and the other the water chiller unit—with 480 VAC and 120 VAC electrical power fed from external hardware at the test site, and data capture and controls achieved using four different, independent software packages. From 2017 to 2019, in support of a densified hydrogen loading test program, the entire system was repackaged in to a single, 40’ (12 m) shipping container, including the refrigeration system, water chiller, and electrical power distribution hardware, and controls were consolidated into a single Allen Bradley PanelView. This new system constitutes an easily portable, stand-alone, 20 K Brayton cycle helium refrigeration system, with the only external interfaces being vacuum jacketed helium lines to/from the cold-box, 480 VAC electrical power, LN2 feed, and shop air or nitrogen pressure for valve actuation. Details regarding the design, build-out, and testing of the system will be presented and discussed.
The National Synchrotron Light Source-II is an electron storage ring with a circumference of 792 m located at Brookhaven National Laboratory (BNL) in Upton, N.Y. The fourth-generation light source with an electron beam of 3 GeV using current up to 500 mA will be able to produce high intensity X-ray radiation and high-intensity infrared, as well as visible and ultraviolet light. The storage ring contains two superconducting radio frequency sections that will boost electrons during their circulation. These two SC RF sections are cooled by liquid helium supplied from an independent cryogenic system.
The cryogenic system is a closed loop helium system that consists of compressors, liquefier/refrigerator (Cold Box), manifold box, and a valve box. The system liquifies gaseous helium to a temperature of 4 K and delivers to the SC RF cavities by means of vacuum jacketed transfer lines. Beginning in 2017, the cryogenic system has undergone a number of upgrades, including the addition of a second valve box, a fourth buffer tank, an inline helium purifier and a Bonitron capacitor backup for our compressors. In addition, the manufacturing of a second Cold Box and Dewar are underway and scheduled for a 2024 installation.
The Proton Improvement Plan-II (PIP-II) is a crucial upgrade to the Fermilab accelerator complex, featuring a new 800-MeV Superconducting Radio-Frequency (SRF) linear accelerator (LINAC) with 23 cryomodules operating at 2K. The LINAC thermohydraulic conditions are satisfied by the cryogenic subsystems: Cryogenic Distribution System (CDS), a helium refrigerator cold box (CB), a warm compression station (WCS) and a helium recovery system (RSYS). The accelerator has a strict requirement of non-thermal cycling of the LINAC cryomodules during planned and unplanned subsystem outages.
This paper presents an integrated operating modes analysis of the of the LINAC/CDS thermohydraulic loads satisfied by the CB/WCS cooling system supported by the RSYS inventory management system. The study is based on latest cryoplant and CDS engineering deliverables, as well as the recent performance data from single cryomodule qualification tests performed at the Fermilab PIPII IT test stand. The study evaluates both normal and abnormal operating modes, with a focus on identifying integrated scenarios that put subsystems components under stress.
The conclusions of this study will help build redundancy to reduce the risk of thermal cycles during planned and unplanned subsystem outages.
Superconducting magnetic separation is a new type of wastewater treatment technology, which is the product of the integration and innovation of multiple fields such as cryogenic technology, superconducting magnets, environmental protection technology, and integrated mechanical design. This new technology has demonstrated many advantages. And it play a role in promoting the use effect of existing technologies through the combination and application of this technology with other wastewater treatment technologies. Results have shown that compared with traditional flocculation sedimentation wastewater treatment technology, this technology can save 30-45% of flocculant dosage, which can reduce flocculant cost and sludge production, so it is of great significance in terms of economy and environmental protection.
Thermal stability is one of the important parameters for the conduction cooled superconducting coil. In the conduction cooled superconducting coil, the only cooling source for the coil is the cold head of the refrigerator, thus a good thermal contact between the coil and the cold head is required. In general, an impregnation is inserted between the wires in the coil. For example, epoxy and greases are used in the superconducting coil as the typical impregnations. However, voids are easily caused in the impregnation during the coil fabrication because these impregnations are high viscosity, and these voids can cause the performance degradation of the coil. In addition, these impregnations are difficult to remove after the coil fabrication, thus the superconducting wire cannot be recycled. In this study, we proposed a new method using ionic liquids as the impregnation. The ionic liquids have many unique properties. For example, the ionic liquids are low viscosity at the room temperature and the crystalline or glassy at lower temperature. Hence, by using ionic liquids, the fabrication of the coils without voids in the impregnation can be handle easier than by using epoxy. In addition, the vapor pressure of the ionic liquid is very low under the high vacuum. Furthermore, the superconducting wires can be recycled because the ionic liquids are low viscosity at room temperature. We prepared the epoxy and two types of ionic liquids as the impregnation. The thermal conductivities of the epoxy and two ionic liquids were measured by a steady-state heat flow method, when the temperature of the impregnation was varied from 40 to 90 K. As a result, the thermal conductivity of ionic liquid is higher than that of epoxy, which shows that ionic liquid may be applied as a heat drain material for a conduction cooled coil. The results provide fundamental data for improving the thermal stability of conduction cooled superconducting coils.
The development of cryogenic technology has greatly reduced the cost of large-diameter superconducting magnets and the difficulty of operation, making it possible for industrial fields. Our team has developed a large-diameter (room temperature aperture of more than 400 mm) superconducting magnet with direct-conduction cooling by a single GM refrigerator, which has improved the cooling efficiency, thermal stability and safety of the superconducting magnet, and it has been adapted in wastewater treatment. Based on the strong magnetic field generated by the superconducting magnet as well as carefully designed magnetic gradient, a series of devices have been developed and applied in several projects in China. In addition, an automated, continuous high-gradient magnetic separation system, as well as a cleaning system and a magnetic species recovery system have been developed to achieve efficient, continuous and stable operation of device. Furthermore, an integrated superconducting magnetic separation wastewater treatment device has been formed through integrated design, which has demonstrated significant performance on the treatment of chemical oxygen demand (COD), total phosphorus and suspended solids, et al.
Superconducting motors and generators are known to have advantages in lightening weight and improving efficiency compared to normal conducing machines, and researches on superconducting motors using liquid hydrogen also have recently been widely conducted. To cool the superconducting rotating machines, a cryogenic rotary coupling is required to supply and return the cryogenic fluid and the development of a sealing structure in the cryogenic rotary coupling is essential to minimize fluid leakage.
This study describes the design and performance evaluation of non-contact Labyrinth seals, not contact-type seal structures, in which power loss and thermal load due to friction occur. Inclined multiple flow paths are applied to further minimize leakage in the high-speed rotor due to the centrifugal force. Prior to fabrication, the leakage flow rates are simulated for the various shapes of the flow paths and the rotational speed using the Computational Fluid Dynamics (CFD) method. The performance of the seal designed using liquid nitrogen is evaluated by measuring the leakage flow rates at a given differential pressures using a performance evaluation apparatus. The results of the study will be used in the development of cryogenic rotary coupling with supply and return flow paths at cryogenic temperature.
It is critical to understand the thermal environment of superconducting electronics and supporting hardware for the circuitry to function as designed. We present a methodology to approximate thermal properties and capture the unique physics (i.e., acoustic and diffuse phonon transmission at boundaries and electron-phonon interactions) that occur in these systems. The methodology approximates thermal conductivity of materials using the Wiedemann Franz law, Debye theory of solids, and BCS theory. We utilize the outlined method to develop a fully 3D model in COMSOL Multiphysics and compare it to a simple 0D approximation, highlighting the value and accuracy of the simple model.
The heat transfer characteristics of regenerator in regenerative coolers such as pulse tube and Stirling coolers is important. Various methodologies of characterizing the Nusselt number between the regenerator matrix and working fluid have been established and applied. However, most of the existing formulas are based on the results of steady-state flow or low-frequency oscillating flow. In this paper, a tube model with finite wall thickness is built to investigate the Nusselt number in a regenerator under different flow conditions. The results indicate that within the Valensi number range typically used in coolers, the Nusselt number of oscillating and steady flow are numerically similar. But under extremely high Valensi numbers, significant differences are observed. This paper will generalize the variation features of the Nusselt number with the Valensi number in a simplified regenerator. Moreover, the applicability of the conventional theories under high Valensi numbers will be evaluated.
In a pulse tube refrigerator, the multi-bypass structure establishes a gas channel in the radial direction between the pulse tube and the regenerator. In the experiment, it was observed that the flow area of the gas channel had a significant impact on the performance of the pulse tube refrigerator and that there exists an optimal flow area that drives the cold head to reach the minimum temperature. The finite volume method was adopted to solve the flow field in the pulse tube refrigerator with a multi-bypass structure. Meanwhile, the thermodynamic states of several gas parcels were also tracked in the Lagrange view. It is demonstrated that when the multi-bypass structure has a suitable flow area, some vortex cores would be generated in the pulse tube. Furthermore, the influence of the multi-bypass structure is explained with the vortex viewpoint on the pulse tube refrigerator.
Design of two-stage Stirling cryocooler with a unique long second expansion space volume is proposed to effectively reduce the displacer length and mass. The thermodynamic performance of this cooler which is similar to a pulse tube cryocooler with the warm-end expander is investigated by the numerical analysis. The long expansion space at the second stage behaves as a pulse tube with a temperature gradient along the longitudinal direction. Similar to the conventional two-stage Stirling cooler, the displacer simultaneously recovers the expansion work at the first stage expansion space and the warm end of the second stage expansion space. Although the long expansion space is an additional compliance volume to the second stage, the stepped displacer can still produce sufficient phase shift for both regenerators at the first and the second stages. This configuration brings the advantage of recovering the expansion work and eliminating the moving part at the coldest region of the cooler. The designed two-stage Stirling cryocooler has a cooling power of 10 W at 50 K and 30 W at 100 K with the input PV power of 404 W. The detailed thermal analysis presents its characteristic with the comparison to a conventional two-stage Stirling cryocooler which has the same displacer diameters.
With the improvement of passive thermal insulation technology, the heat leakage of cryogenic storage tanks has been effectively reduced. However, with the growth of storage time, the accumulation of heat leakage inevitably makes the liquid in the tank continuously gasification, resulting in the quality loss of the liquid. Zero-boil-off storage systems, which generally use cryocoolers to re-condense the evaporated gas, can effectively solve the above issue. In this paper, a zero-boil-off storage system based on high-frequency pulse tube cryocooler cooling is studied numerically and experimentally. The storage characteristics of directly re-condensing evaporating gas and refrigerating the stored cryogenic liquid are compared. Numerical results of liquid hydrogen and liquid nitrogen, and experimental results based on liquid nitrogen will be presented.
Pulse tube cooler has the advantages of higher reliability and longer MTTF compared with Stirling cooler due to the elimination of moving components at the cold end. Pulse tube cooler working in the liquid hydrogen temperature region has already become a strong candidate in the fields of space science and high-temperature superconductivity. However, the current efficiency of the pulse tube cooler at liquid hydrogen temperatures is still low. In this paper, a two-stage thermally-coupled Stirling-type pulse tube cooler working in the liquid hydrogen temperature region is simulated. The first and second stages use independent ambient displacers as phase shifters. The middle of the second stage regenerator and pulse tube will be pre-cooled by consuming part of the cooling capacity of the first stage through the intermediate heat exchangers. The simulation results show that the pulse tube cooler can reach a higher relative Carnot efficiency due to the improvement of the phase distribution of the whole system by using ambient displacers. Meanwhile, the influence of factors such as charge pressure, frequency, pre-cooling position and pre-cooling temperature on the system performance will also be discussed.
A three-stage pulse tube cryocooler driven by 500W Stirling compressor is built and tested. To improve the phasing capability of the system, a double-inlet structure is introduced between the hot end heat exchanger and the pulse tube at all stages. In this paper, a simulation study and experimental verification of the reasonable opening of the double-inlet are carried out, and the reasons for the variation of the differences in the optimal values among them are analyzed. In addition, experimental analysis was conducted on the influence of operating pressure, operating frequency and filling pressure on the cryocooler, and the analysis showed that whether the refrigeration system is in the optimal phasing environment has the greatest influence on the experimental results.
Limited by real gas effects which stick out in the critical temperature range, it is a challenge for high-frequency pulse tube cryocoolers to obtain the liquid helium temperature or blow. The influence of real gas effects on the cold-end refrigeration performance of a low-temperature regenerator working in the liquid-hydrogen to liquid-helium temperature ranges was investigated primarily by theoretical analysis and simulation in this paper. Besides, the critical parameters hindering the achievement of liquid-helium temperature were given, and the design and optimization direction of the high-frequency regenerator working at 4 K was pointed out. A three-stage high-frequency pulse tube cryocooler was designed, built, and tested. The composite refrigeration process uses a single-stage 77 K cooler to pre-cool a two-stage gas-coupled high-frequency pulse tube cryocooler. The no-load temperature has been reduced to 2.4 K using 4He as the working gas, and a cooling power of 26 mW at 4.2 K was obtained.
A clear boiling delay was observed during imbibition of room temperature liquids into capillary channels, in which nucleate boiling is postponed to a temperature above the saturation temperature of the liquid. This boiling delay is also expected to influence the wicking behavior because similar effect are involved, for example the effect of surface tension, viscosity and evaporation. Wicking into microstructures of porous materials often happens at elevated wick temperatures, especially in cryogenic applications. The knowledge of boiling delay can be applied in for example cryogenic propellant management devices used in space applications or dry-shippers a container lined with porous material that absorbs liquid nitrogen.
Several imbibition regimes were observed depending on the channel temperature. Typically, the imbibition velocity increases with channel temperature due to the reduction of viscosity until the saturation temperature of the liquid is reached. Once the temperature exceeds the saturation temperature of the liquid, the evaporation rate at the surface of the meniscus accelerates rapidly, however nucleation inside the liquid phase does not occur initially. The effect of evaporation gives rise to a reducing imbibition velocity, which can be explained by two effects. The increase in momentum of the vapor during evaporation gives rise to a backpressure and the increased vapor velocity increases the viscous contribution of the vapor, which is often neglected in the low temperature regime. At higher elevated temperature the nucleation of vapor bubbles is no longer delayed and vapor is no longer only generated at the liquid front, which is followed by a regime where the liquid no longer enters the channel similar to the Leidenfrost effect. At cryogenic temperatures the specific heat capacity and latent heat of evaporation can be an order of magnitude lower than their room temperature counterparts, therefore a setup is designed to study the boiling delay at cryogenic temperatures.
The experimental setup must adhere to several requirements regarding temperature control, background gas control, and optical access. A method to reduce the temperature of the capillary channel to below the saturation temperature of liquid nitrogen is developed. At this temperature nitrogen and oxygen begin to condense on parts of the setup, therefore the background gas has to be controlled taking into account the evaporation of nitrogen from the channel. An optical setup is being implemented to have visual access to the test section without compromising the thermal insulation properties of the setup. The challenges for this experimental setup are discussed together with their solutions.
Spray cooling is the primary method for conducting chilldown and fill of cryogenic propellant tanks. In a typical spray injection process, a liquid sheet/jet that exits the spray nozzle undergoes primary breakup by the development of surface instabilities. Droplets and ligaments generated after the primary breakup undergo secondary breakup to create a dispersion of droplets, which extract heat on impact with the tank walls. In the existing literature, there is limited data on the primary breakup of cryogenic sprays and their detailed visualization. Moreover, an insight into the spray characteristics such as primary breakup length and cone angle is vital to the development of computational models. In this investigation, optical diagnostics of cryogenic spray breakup and measurement of spray characteristics have been conducted. Liquid nitrogen is the selected cryogen for the analysis. To capture the transient nature of spray breakup after the injection, a novel shadowgraph diagnostics technique is developed to photographically freeze the spray motion. Spray characteristics such as cone angle and primary break-up length are obtained from the shadowgraph. A brief discussion is presented on droplet velocity measurement using particle image velocimetry. The comprehensive experimental dataset obtained not only provides insights into the mechanism of spray formation for cryogenic fluids but also helps in designing of spray cooling system for tank chilldown.
To study the quenching characteristics of different materials in cryogenic liquid baths, transient temperature measurements of high accuracy are necessary. Thermocouple is an ideal tool for these applications because of their low self-heat capacity. However, they require calibration before usage. Typically multiple fixed point temperatures are used. The common fixed point temperatures are water-ice bath melting temperature, dry ice sublimation temperature, and boiling temperature of liquid nitrogen. It is important to note that there are uncertainties associated with dry ice and liquid nitrogen temperature inherent to the heat and mass transport phenomenon at their phase-changing interface or inside the bulk medium. The dry ice temperature is influenced by the mass transport phenomenon occurring at the interface between dry ice and the ambient surrounding it. In a typical lab environment, dry ice temperature is significantly lower than the commonly quoted sublimation temperature of -78.5 °C. In the case of liquid nitrogen stored in a cryostat, temperature gradients are present in the liquid bath. This paper describes a protocol for calibrating thermocouples by accurately defining and using fixed point temperatures of liquid nitrogen slush and dry ice in a saturated environment.
Hydrogen is seen as a key energy carrier for a future CO2-neutral society. The high energy density of liquid hydrogen (LH2) is advantageous for transport and for a number of applications, especially in the mobility sector. Within the framework of the national hydrogen lead projects of the BMBF [1], KIT [2] is working with project partners of the technology platform "TransHyDE" in the lead project "AppLHy!" on the transport and application of liquid hydrogen. Therefore, the characterization of materials under cryogenic and liquid hydrogen conditions is needed in terms of interaction and possible degradation. Within this contribution different material-testing devices will be presented, such as a pre-charging device, operating at various H2-pressures and different temperatures. An in-situ charging device as well as mechanical testing machines operating from room temperature to 20 K will be also presented [3]. Moreover, the contribution will also show the H amount measurements after charging at several conditions.
[1] https://www.wasserstoff-leitprojekte.de/
[2] https://www.kit.edu/kit/pi_2021_078_wasserstofftechnologien-kit-forscht-in-allen-drei-leitprojekten-des-bundes.php
[3] https://www.itep.kit.edu/148.php
In recent years, due to the emerging growth of industry sectors focused on achieving Net-Zero energy sources; the research, development, and application of fibre-reinforced polymer (FRP) composites in the cryogenic liquid storage and distribution fields has grown significantly. When exposed to extreme temperatures, FRP composites can exhibit significant changes in their properties, as reported in literature. The development of capabilities for mechanical testing of FRP composites under cryogenic conditions is of the utmost importance to determine material performance and provide assurance of material quality.
At present, there is a limited number of literature sources that provide consistent and reliable mechanical test results generated from cryogenically testing FRP composites. This is due to the lack of standards available to provide guidance on test methods, specimen dimensions, apparatus, and instrumentation for the successful characterization of mechanical properties of FRP composites under these extreme temperatures. This is considered a major barrier to the increased uptake of FRP composite materials and processes in liquid hydrogen (LH2) and liquified natural gas (LNG) distribution and storage applications, especially when compared to metals.
The aim of this study is to assess the applicability of existing tensile and compressive test standards, as well as investigate and validate the mechanical properties of FRP composites with different resins, fibres and layup compositions, when tested as low as -165 °C. The experimental findings have provided preliminary evidence of material-dependant behaviour in cryogenic temperatures, but mainly highlighted the room for improvement in terms of specimen and test preparation, equipment and practices, in order to be able to confidently characterise FRP composites under these conditions.
Cryogenic epoxies must have application-relevant electrical, thermal, and mechanical characteristics for safe operation for the life of the device. Appropriate testing techniques and protocols are necessary for epoxy material selection and qualification. Epoxies for cryogenic applications need to be tested at the cryogenic conditions of the device. We have developed a novel test protocol to evaluate samples' interfacial shear stress (IFSS) at room temperature that tracks load transfer and isolates the failure mode between materials. As part of our continued research, we are modifying the apparatus and technique to measure the IFSS of two cryogenic epoxy interfaces with other materials. The first interface is between the cryogenic epoxy and high-temperature superconducting (HTS) material to explore the epoxy as the electrical insulation for HTS power cables. Our research identified cryogenic epoxies with mechanical flexibility at room temperature and showed promise as electrical insulation. The stress/strain evolution of the interfacial bonding between the epoxy and HTS tapes to failure was measured to assess its ability to support the loading under cryogenic conditions. Measurements were performed in a bath of LN2 to evaluate the interfaces after multiple thermal cycles. The probability of delamination of the epoxy coating from the conductor was assessed. Delamination and void formation at the HTS tape/epoxy interface will cause partial discharge and the eventual failure of the electrical insulation systems of HTS cables.
The second aspect of the study investigated the mechanical interfaces of thermal insulation blanket mount retainers with cryogenic storage tanks. The adhesive properties of the cryogenic epoxies need to prevent delamination from the storage tank wall at cryogenic temperature. Test samples were characterized in a bath of LN2. Care was taken when performing the measurements to avoid excessive thermal shock. Microscopy was performed to assess the fracture modes for both the electrical insulation and thermal insulation blanket retainers. The viscoelastic performance of the cryogenic epoxies was tested using frequency sweeps at various temperatures. The models of thermomechanical fracture developed were validated to assess the digital twin accuracy. The model assumed viscoelastic conditions, and the time-temperature superposition (TTS) principle was employed to extend the simulation prediction to an extensive range of frequencies and temperatures. The results of the models and experiments were used in designing and evaluating material thermomechanical performance and bonding strength to understand interfaces at extreme conditions. Commentary will also be provided on potential modifications to the experimental setup to allow measurements at cryogenic temperatures, and the data will be discussed in the context of the applications.
Passive thermal control is vital in space, especially for extended missions involving cryogen storage needing protection from sunlight. Long-term cryogen storage in space can be possible when the exterior thermal coating can reflect most of the incident sunlight. Additionally, high emissivity in the longwave infrared wavelengths allows passive cooling by taking advantage of low-temperature conditions in deep space. Such desirable radiative properties minimize cryogen loss and could obviate the need for active cooling strategies to store cryogens. This study aims to develop a thermal coating with wavelength-selective characteristics using polymeric materials that scatter sunlight with minimal absorption, resulting in high solar reflectance. Furthermore, these coatings allow emission in infrared wavelengths, making them suitable for deep-space missions requiring extended storage. The study chose polymers and surface morphologies suitable as solar reflectors and are lightweight, compact, and easily manufacturable. This study focuses on multilayered nanofibers of polytetrafluoroethylene (PTFE), and polyethylene-oxide (PEO) made using the electrospinning technique. Since electrospinning offers control over fiber geometry, this study determines how fiber geometry affects solar reflectance and infrared emittance.
We analyze light propagation through several layers of electrospun nanofibers to determine the spectral reflectance, absorptance, and transmittance by solving the Maxwell equations. While focusing on the size effect, we consider two-dimensional (circular) features to resemble the randomly arranged cylindrical nanofibers achieved by electrospinning. The analysis involves solving Maxwell’s equations for a given fiber geometry and arrangement using the constituent material’s wavelength-dependent refractive index. As light propagates through the random structure, it is reflected, absorbed, or transmitted by interacting with the multiscale fibers. The amount of incident light transmission, reflection, and absorption are then obtained using the electromagnetic field distribution across the material. Consequently, this predictive model determines the fiber geometry most suitable for thermal coating for a chosen material and within fabrication constraints. The model is validated by measuring the spectral reflectance and transmittance of the electrospun nanofibers using spectrophotometers interfaced with integrating spheres.
Among all geometric parameters, the spectral hemispherical reflectance of PTFE films shows a strong dependence on thicknesses. The experiments and simulations indicate that the reflectance increases with increasing thickness. The transmittance, on the other hand, drops with increasing thickness, and the film becomes opaque. In addition to the thickness effect, the model also determines the effect of other geometric parameters, such as fiber diameter and spacing, indicating the scope for design optimization. Finally, both model and experiments indicate that an average solar reflectance of 0.988 can be achieved using electrospun PTFE:PEO (90:10) nanofibers of thickness 1 mm. On the other hand, spectral emittance at a wavelength of 8 μm was found to be 0.9. Based on these observations, we believe the PTFE/PEO films are promising thermal coatings for cryogen storage.
Acknowledgments:
The authors acknowledge the support of the National Aeronautics and Space Administration under Grant No. 80NSSC21K0072 issued through the Space Technology Research Grants.
The development of hydrogen-electric aircraft propulsion offers a perspective for emission-free aviation. Liquid hydrogen, which is stored in cryogenic tanks at 20-30 K, is used as energy source and to cool the electric engine. This increases power density and efficiency of the electric engine. In this application, the components are exposed to low temperatures and direct contact to hydrogen, which can highly affect the mechanical properties of the material.
In this work, various additive manufactured metallic alloys were investigated for the effect of hydrogen on mechanical properties in tensile and fatigue tests. Tests were conducted at room temperature and at 77 K in liquid nitrogen. To study the effect of hydrogen, the tubular specimen method was used, in which a deep hole is drilled through the longitudinal axis of the specimen and filled with hydrogen during testing. This allows to simultaneously expose the specimen to pressurized gaseous hydrogen from the inside and to cool it with liquid nitrogen from the outside during testing. By examining the fracture surfaces under a scanning electron microscope, a deeper insight into the damage behavior could be gained.
These investigations on additive manufactured materials show several effects on the mechanical properties caused by anisotropy due to build-up direction, low temperature and hydrogen.
Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904E.
Measurement of cryogenic propellant pressures (liquid oxygen and liquid hydrogen) of rockets is very critical for their successful launch. These pressure measurements are carried out using integral diaphragms pressure transducers. Material is machined out from both ends of the circular rod made of precipitation hardened martensite stainless steel (APX4), such that thin circular diaphragm is formed at the centre. One surface of the diaphragm senses the input propellant pressure and the other side senses the stress induced with the help of strain gauge bonded on the surface. The diaphragm senses input pressures and gets proportionally deflected at the centre (within the elastic limits) due to the stress induced. The deflection is transmitted to the strain gauges which in turn produces a measurable electric output through wheat stone bridge network. Output electrical signals are calibrated in units of pressures. These transducers are expected to exhibit dimensional for the reliable performance throughout their useful life. The precipitated hardened martensite stainless steel used for machining pressure transducer does not contain hundred percent martensite and possesses certain amount of austenite (around 3-4 %) known as retained austenite. Martensite has strong and hard microstructure as compared with austenite which is soft, tough and ductile. This unstable retained austenite slowly gets converted to freshly formed martensite with time which has different coefficient of volumetric expansion. Differential volumetric expansions within the metal cause dimensional changes and produce dimensional instability to causing zero shift and drift in output readings. The conversion from retained austenite to martensite is faster in the presence of high residual stress. Cryotreatment is a proven technology to reduce such residual stresses. Cryotreatment is a process where the material is gradually cooled down to cryogenic temperature and exposed to the cryogenic environment for prolonged time and slowly warmed up to room temperature.In the present experimental study, the machined diaphragms were cryotreated in a dedicated cryotreatment system using liquid nitrogen as the cooling medium. Diaphragms were cryotreated gradually cooled down to 98K, maintained at this temperature for 36 hours and gradually warmed upto room temperature. After cryotreatment, they were tempered at 673K for one hour in vacuum furnace. Dimensional stability analysis of both regular and cryotreated diaphragms were carried out using Thermo Mechanical Analyser (TMA). Results indicated significant enhancement of dimensional stability of diaphragms which were subjected to cryotreatment.
Keywords: Dimensional stability, Stress, Strain gauge, Austenite, Martensite, Cryotreatment
Introduction
Insulating materials used in superconducting magnets for fusion reactors are exposed to radiation at the cryogenic temperature of liquid helium temperature. ITER, an experimental nuclear fusion reactor, uses glass fiber reinforced plastic (GFRP), which is a 3:2 mixture of epoxy resin (EP) and cyanate ester (CE) (40 wt.% in CE content) with excellent radiation resistance, as an insulating material that can maintain mechanical strength and insulation performance under such an environment. However, this composition was determined through strength tests at room temperature and liquid nitrogen temperature. In this study, four types of insulating materials with different resin compositions were prepared, and the interlaminar shear strength (ILSS) was measured at room temperature, liquid nitrogen temperature, and liquid helium temperature before and after γ-ray irradiation to evaluate the effect of resin composition on the absorbed dose dependence and temperature dependence of ILSS, in order to determine the optimal resin composition in consideration of mechanical strength at liquid helium temperature.
Experimental methods
Four types of GFRP were prepared by vacuum-impregnating a mixture of EP and CE resins with CE content of 0, 20, 40, and 60 wt.%, and then heating and curing the laminated glass cloth. For resins with 0 wt.% CE, polyetheramine was used as the curing agent. These GFRPs were fabricated into the double-notched shapes, and then irradiated with 60Co γ-rays at room temperature and in the air atmosphere, and then subjected to ILSS test at room temperature, liquid nitrogen temperature, and liquid helium temperature.
Results and discussion
Regarding the absorbed dose dependence, the ILSS of GFRP with 0 wt% CE decreased by γ-ray irradiation, but the ILSS of GFRP with more than 20 wt% CE did not decrease after irradiation. This indicates that the addition of CE enhances radiation resistance. As for the temperature dependence, the ILSS of irradiated GFRP with 0 wt% CE increased with decreasing temperature, whereas the ILSS of GFRP with 20 wt% CE increased with decreasing temperature from room temperature to liquid nitrogen temperature, whereas decreased when cooled to liquid helium temperature. This is considered to be due to the formation of a rigid molecular structure in the resin by the addition of CE, which leads to embrittlement at cryogenic temperatures.
Conclusion
The temperature dependence of ILSS of specimens after room temperature irradiation was found to be different between EP without CE and those with CE. It was also found that the temperature dependence was changed with the CE content. In order to clarify the optimal composition for practical use, it is necessary to examine the effects of low-temperature irradiation and temperature history in the future.
Acknowledgments: This study was supported by QST Research Collaboration for Fusion DEMO, and the NIFS Collaboration Research Program (NIFS22KIEA006) of the National Institute for Fusion Science. Materials for testing were provided by Arisawa Manufacturing Co., Ltd, Shouritu Kogyo Co., Ltd., and Risho Kogyo Co., Ltd.
Keywords: insulating materials, γ-ray, glass fiber reinforced plastic (GFRP), interlaminar shear strength (ILSS), liquid helium temperature, cyanate ester, embrittlement
Due to the high current carrying performance under high field and low temperature (<20 K), REBCO tapes exhibit a strong potential of future fusion magnets application. The characteristics, such as anisotropic and multi-layered structure, the stress/strain sensitivity of critical current carrying performance, make them not easy for CICC development, which is very important to achieve practical application for fusion devices. In institute of Plasma Physics, Chinese Academy of Sciences, two kinds of CICC design concepts were proposed. The cable was twisted from sub-cable manufactured by winding the REBCO tapes around a stainless steel spiral tube. In addition, to increase the intensity of the cable, the sub-cable was assembled together with the Cu tube or Cu bar having machined slots outside. Research activities were carried out to find a solution for central solenoid (CS) coil for the next generation fusion device construction. Till now, processes including sub-cable winding, cable twisting, short length CICC assembly and compaction as well as joint termination soldering are being developed for design and performance qualification. CICC sections have been manufactured, totally 210 REBCO tapes were used for each kind of design. Tested critical currents of around 20 kA at 77 K, self-field indicate no obvious degradation happened during the CICC manufacturing processes. Two CICC sections with a length of around 2.7 m, one for each design concept, have been delivered to Sultan lab for performance qualification under a maximum background field of 10.8 T.
Advancements are required in superconducting magnets for safe, reliable, economic, and environmentally benign operation in high-energy radiation environments such as nuclear fusion devices. Degradation of electric insulation, when exposed to high levels of radiation or high temperature of fusion devices, must be minimal. Innosense LLC (ISL) in collaboration with Florida State University and the University of California Davis developed metal oxide nanoparticle incorporated organic polymer composites (MONAP) to be used as wrap-able, radiation-resistant electrical insulation. MONAP builds on ISL’s proprietary organic polyurethane (PU)-polyimide (PI) copolymer (PUPI), thermally and mechanically robust polyvinylidene fluoride (PVDF), and metal oxide (inorganic) nanoparticles (NPs) such as silica (SiO2), magnesium oxide (MgO) and zirconium oxide (ZrO2). The composite matrix is suitable for the desired temperature range of future fusion devices - cryogenic temperature to 100 oC and in the presence of ionizing nuclear radiation. This paper discusses MONAP and its characteristics of pot life, adhesion/bonding properties, flexibility, wrap-ability, thermos-mechanical stability, and dielectric strength before and after exposure to neutron radiation. Ongoing developments in optimizing MONAP formulation, scale-up methods, and commercialization potential are also discussed.
Current sharing is a critical self-protecting mechanism for non-insulating coils and multi-strand cables. Current sharing can be controlled by the contact surface resistance between superconductors. We have found that the contact resistance of REBCO coated conductor can be modified by applying press, sintering, and metal-plating. In our previous work, we conducted steady-state FEM analysis and demonstrated that current sharing in a multi-strand REBCO cable is determined by both inter-strand contact resistance (ICR) and inter-strand thermal resistance (ITR). In this work, we continued this study, but including the transient (time dependent aspects of current sharing small REBCO cables. We constructed a three-tape cable with a defect that could either be pre-existing or be initiated at a given time, located in the middle tape (at the strand center, but across the entire tape width). The defect length was 0.1 mm, and carried 10% Jc. The current was supplied through the cable, and we captured continuous animation of current sharing in the cable for 0.1 s. By using different values of inter-strand electrical contact efficiency, η (η=ICRcontact area), and corresponding inter-strand thermal insulance, ω (ω=ITRcontact area) as input parameters, the simulation results showed current distribution along the cable during the current transferring process.
Australia’s energy policy settings at Federal and State level offer opportunities for a power transformation unmatched in format and content since the impact of widespread electricity transmission more than 50 years ago. These settings are driven by regulation that links the energy sector network to low (or zero) emissions targets and by network decentralization that enables greater use of renewable energy sources. Projections for renewable energy generation in Australia by 2050–2060 suggest increases between 8- and 40-times existing network market capacity [1]. Uncertainty in this range of values depends on projected risk profiles and approaches taken to reduce Australia’s scope 3 emissions from energy exports currently dominated by coal and liquefied natural gas (LNG).
Renewable energy capacity in Australia is currently ~36% of total energy generation [2] with targets of ~80% in many jurisdictions by 2030-35. These target(s) presage ambition by policymakers in Australia to become a Hydrogen Superpower for the global clean energy industry and, by implication, a critical source of green hydrogen. Thus, production, storage, distribution and use of hydrogen will play a significant role in the energy transformation to 2050 and beyond. All jurisdictions in Australia have developed strategic plans for R&D, infrastructure build or rebuild, skills training, funding incentives and investment in a hydrogen facilitated energy transformation. Liquefaction is well established in Australia with 21 LNG trains operating along the western, northern and eastern coastlines. However, liquefaction of hydrogen, while nascent at industrial scale, has only recently been facilitated by inter-governmental and corporate engagement using existing resources.
For example, the Hydrogen Energy Supply Chain (HESC) concept promulgated by Japanese companies more than a decade ago [3], achieved a key demonstration step in early 2022. This step involved commissioning of a small-scale liquefaction plant (250kg H2/day) at Port Hastings to transfer LH2 for sea-borne shipment to Japan. Hydrogen was produced via gasification from brown coal in the Latrobe Valley. The liquefaction plant and port transfer facilities are the first such technologies installed in Australia. More than five other hydrogen liquefaction projects of commercial scale have been announced in Australia to date. These projects include use of renewable energy to produce hydrogen and a combination of gas and liquid storage capacity to address emerging export markets (e.g., LH2 or NH3).
Two web portals are useful resources for current compilations of hydrogen-focused initiatives driving the transformation of Australia’s energy industry: HyResource and HyResearch [4]. The former documents >110 active and 15 inactive industrial projects, while the latter lists over 280 hydrogen-related R&D projects currently active in Australia. R&D on liquefaction is focused on the ortho-para transition, distribution and/or modularity of storage options, value-chain modelling, materials for magneto-caloric refrigeration and energy storage systems integration. Examples of these R&D projects will be detailed in the context of a rapidly transforming policy, investment and operational environment.
[1] Net Zero Australia, Final Results Summary, April 19th, 2023; [2] Clean Energy Australia Report, Clean Energy Council, April 2023; [3] Yoshino et al., Energy Procedia 29, 701-709, 2012; [4] https://research.csiro.au/hyresource/about/ ; https://research.csiro.au/hyresearch/ .
As NASA considers future technologies for aircraft that push towards greater sustainability and a “net-zero” future air transportation system, it is also considering the possibilities of cryogenic alternative fuels. NASA has considered hydrogen as an aircraft fuel since at least 1945 including demonstrations as early as 1957. There have been multiple cycles of interest and development within the agency and while sustainability as a motivation is new, the challenges with implementation are not. While NASA does not currently have extensive investments in aircraft hydrogen technologies, it does have significant expertise with hydrogen for rocket and space applications.
Alternate families of propulsion fuels such as hydrogen, hydrocarbons (methane, ethane, propane, butane, etc..), alcohols of hydrocarbons (methanol, ethanol, propanol, other), natural gas, biofuels, and other, are increasingly being considered for transportation industries and applications, including aerospace and rocket propulsion. And the cryo-cooled versions of these fuels are also increasingly being studied for transportation, since their higher volume densities critically affect cost, viability and performance benefits. The use of liquified-natural-gas (LNG) or bio-LNG has strong benefits for transportation, including much higher energy-per-mass, lower average cost, very high domestic reserves, and broadly located production and distribution piping networks.
This talk will be present about general properties and benefits of families of cryofuels for logistics and thermal-management, focusing mostly on aerospace applications. Relatively unknown fuels and properties will be presented, such as liquid mixtures that have much lower liquid freezing points ~ 60K , that can enable significantly higher power density and more efficient cryogenic power electronics using ultra-pure metals and superconductors. Cryofuels also have important system benefits to provide much larger cooling capacities, which will be important to address the increasingly larger and low-temperature thermal loads resulting from increasing electrification of propulsion.
Acknowledgments. Support by the Air Force Office of Scientific Research (AFOSR) LRIR #18RQCOR100, LRIR #23RQCOR008, and the Aerospace Systems Directorate (AFRL/RQ).
Dual hydrogen-jet fuel aircraft have the potential to reduce greenhouse gas emissions and align with U.S. Aviation Climate Action Plan goals. However, the use of liquid hydrogen solely as fuel introduces significant challenges such as low energy per unit volume, cryogenic storage, and safety risks. Addressing these challenges will require significant investments in infrastructure and technology. The transition to a low carbon aviation sector to meet the stringent mass, volume, safety, and emission requirements economically will require a mix of sustainable aviation fuels including hydrogen, as well as an abundance of renewable energy. Dual hydrogen-jet fuel aircraft with only 14% green hydrogen by weight would require double the total fuel volume of a conventional aircraft, but it could reduce carbon emissions 30%. With less quantities of green hydrogen required, dual hydrogen-jet fuel aircraft will reduce renewable energy, hydrogen infrastructure, and technology demands. The presentation will include an overview of dual hydrogen-jet fuel concepts and describe key sustainable aviation fuel challenges including availability and costs.
As developments of local production of cryogenic fluids on the Lunar or Martian Surface progress, it is important to understand transient system responses to help with the balancing of process plant power and understanding system level operations. During the Cryogenic Fluid In-situ Liquefaction for Landers (CryoFILL) testing, a series of transient oxygen liquefaction tests were completed. These tests included varying liquefaction flow rate, environmental temperature, tank fill level, and effective cryocooler lift while allowing the tank pressure to respond to the input controls. An additional transient test was run at the 90% fill level to determine the impact of injecting the gaseous oxygen at the bottom of the tank, allowing the vapor to bubble up through the liquid. Tests were run in a cyclical nature varying one variable at a time. The control variable was set in a manner to increase tank pressure for a period of time and then subsequently changed in a manner to decrease the tank pressure back to its original value with multiple cycles run for all tests. Tank pressure and system temperature responses were tracked as a function of time with an emphasis on repeatability. Results indicate that of the four variables tested, the environmental temperature is the least important. As expected, the bubbling of the liquefaction gas significantly decreased the pressurization and depressurization rates in the tank at the 90% full level.
Proposed NASA missions to Moon and Mars involve producing cryogenic propellant in-situ to reduce launch mass and requirements. One technique for liquefaction of the gases produced through electrochemical processes is to circulate cold gaseous neon or helium through broad area cooling tubes attached to the outside of the propellant tanks. To determine the performance of this liquefaction process tests were conducted at NASA Glenn Research Center in a 2.1 cubic meter tank with a broad area cooling network (CryoFILL). A thermal/fluid model of the tank and its cooling loops is developed in Thermal Desktop to compare with the test results. Details of the model and the model predictions and comparison to the experimental data from the CryoFILL liquefaction tests are presented here.
Over the past decades NASA has been focusing to develop technology that would allow for production of cryogenic propellants on the surfaces of the Moon or Mars. The in-situ propellant production reduces the amount of propellants needed to be taken to Moon/Mars and ultimately reduces mission cost. Utilizing Lunar/Martian resources, the produced gases are liquefied and stored prior to use on the ascent vehicle. In this paper, a model for the liquefaction process of gaseous propellants in a cryogenically refrigerated tank is presented. The tank is considered to be cylindrical with elliptical top and bottom domes. A multi-node transient model is developed based on the mass and energy conservation principles and wall-gas and liquid-gas interfacial mass and heat transfer correlations. The model is incorporated into the Generalized Fluid System Simulation Program (GFSSP), an MSFC in-house general-purpose computer program for flow network analysis. Description of the model and comparison of predicted results with available test data will be presented and discussed.
The use of cryogenic propellants has and will continue to play an integral role in manned-space exploration due to the high specific impulses offered and its ubiquity in space through in-situ resource utilization. But guaranteeing vapor-free transfer of such low-surface tension liquids is difficult for traditional capillary-action propellant management devices (PMDs). Screen-channel liquid acquisition devices and compliant origami bladders are potential solutions, but to quantify the benefits these technologies offer, this study presents a cast study analyzing the performance metrics of an orthodox vane PMD as a benchmark for comparison. A 0.15 m3 liquid hydrogen tank at 20.3 K and 103 kPa was selected for study. Then assuming no body forces and no heat transfer (for simplicity), a steady-state 1-D differential equation was numerically solved in tandem with two possible wetted area configurations to yield an expulsion efficiency for a given inputted expulsion flow rate. Additional inputs, including vane height and vane number, were parametrically varied between 1 – 10 cm and 4 – 8 vanes, respectively. Future work will determine expulsion efficiencies achieved from maximum expulsion flow rates constrained by choked flow.
Subcooling of cryogenic propellant offers significant advantages for launch vehicles. By densifying the propellant, the propellant tank can be made compact. In addition, onboard subcooling of the cryogenic propellant in the tank efficiently achieves the required NPSH for the rocket turbopump. This means that the amount of venting gas from the tank to cool the propellant and the amount of tank pressurizing gas, such as helium, can be reduced. Therefore, the onboard subcooler is especially advantageous for upper stages. In this study, a cryogenic propellant subcooler consisting of a Joule-Thomson orifice and a heat exchanger was developed. A sub-scale test was conducted using liquid nitrogen as the working fluid, and subcooled liquid nitrogen was successfully obtained. By evaluating the thermal efficiency, the optimum diameter of the Joule-Thomson orifice was found. Considering a practical application of the subcooler for the upper stage propulsion system, the present method proved to have less weight penalty compared to the conventional vent/press operation.
Mechanically connected fluid joints are virtually unavoidable in complex cryogenic system designs. In the case of spacecraft where repair or replacement may be difficult, dangerous, or impossible, the performance of these mechanical joints is critical to mission success. This is especially true for long-duration exploration class space missions where even very low leak rates can eventually lead to significant propellant losses or failure of vital, active cryogenic cooling systems. To aid in future designs, NASA has recently undertaken an effort to quantify the leak rate of Vacuum Coupling Radiation (VCR) fittings from the Swagelok company over the temperature range from ambient to 20 K, both before and after exposure to a launch vibration profile. VCR fittings were chosen based on a survey of NASA cryogenic users that showed these fittings to be routinely used when performing cryogenic thermal vacuum work. A test apparatus employing a cryocooler and a calibrated helium mass spectrometer was developed and validated and used to obtain quantifiable leak rates at a fitting test pressure of 31 bar (450 psig). Three different fitting sizes were tested, 25.4 mm (1/4 inch), 12.7 mm (1/2 inch), and 6.35 mm (1 inch) and two gasket materials, stainless steel, and silver-plated nickel. Each fitting configuration (size/seal material) was subjected to two consecutive cryogenic thermal cycles and measurement tests, followed by a launch vibration test profile at ambient temperature, and then two additional cryogenic thermal cycles and measurement tests. The extensive test program showed exceptional performance for the VCR fittings, with a maximum leak rate on the order of 10-7 sccs across all configurations and test conditions. The design and development of the test apparatus, and test data are presented and discussed in detail.
The superconducting (SC) magnet subsystems for the Material Plasma Exposure eXperiment (MPEX) provide steady state axial fields between 0.05 T and 2.5 T in order to confine the plasma generation and enable the necessary radio freqency source and heating to achieve fusion prototypic environments at different material targets. To maximize the thermal stability of the superconducting magnets and reduce the technical risk given the relative size and number of the superconducting magnets, liquid helium recondensing refrigeration systems were selected at the beginning of the design process to provide the necessary cooling load. As the design has progressed, there has been a significant disruption in global helium supply chains due to pandemic and socio-economic conditions. These conditions warranted a more rigorous assessment of the specific helium usage during acceptance testing, installation, commissioning, and operation to determine best methods to offset the cost and schedule impact to the MPEX project. A comparison was carried out, with respect to the cost of a modest helium recovery system and the planned usage for the SC magnet subsystem, to determine the cost of helium per liter and cost of electricity, where conservation and recovery would be feasible.
This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan
Prior to the invention of the vacuum flask by James Dewar in 1895, cryogenic temperatures below 100 K could not be maintained for very long. The development of the modern cryostat was an extension of the basic Dewar vacuum flask. The design of the cryostat and its insulation system is a function of the cryostat's intended use. The type of refrigeration available also influenced the development of the cryostat and the insulation systems that were part of that cryostat. In recent years, the availability and the cost of helium has been a significant factor in cryostat design and the methods used to cool and cool-down cryostats. This paper will explore the historical development of today's cryostats and how they may be tied to the source of cryogenic cooling. This paper will focus on cryostats that are subject to the force of gravity or centrifugal forces.
GSI/FAIR is planning for a Helmholtz Linear Accelerator (HELIAC), a continuous-wave linear accelerator that will allow for new research opportunities with a continuous particle beam. The first cryogenic accelerator module of the HELIAC, the so-called advanced demonstrator, has been designed, manufactured and tested at 4 K. The cryostat of the advanced demonstrator has a length of about 5 m and a diameter of 1.7 m and will contain four superconducting accelerator RF cavities and two superconducting solenoids.
Cryoworld has designed and manufactured the cryostat in collaboration with GSI Darmstadt and Helmholtz Institute Mainz. The cryostat has unique features making it first of its kind. Four large doors in the vacuum jacket allow access to the internal components, and to assemble the RF-power couplers and the current leads. A dedicated suspension system of the cavities and solenoids is designed from scratch to align the components accurately and to ensure that the centre line stays within a cylinder of 0.2 mm during evacuation and cool down. Further, due to space restrictions, the cryogenic valves, safety relief devices and instrumentation required for process control are included in the cryostat.
The advanced demonstrator cryostat was cooled down to 4 K and tested with identical dummy cavities and with the original solenoids to demonstrate the mechanical behaviour under cryogenic conditions. By using special targets and a high-end optics camera, the actual displacement of the components during evacuation and cool down was observed. The solenoids have been successfully tested with a heavy ion beam. Further, instrumentation and heat loads were checked.
This contribution will present the design and manufacturing of the cryostat in detail. It will discuss the special design features, the suspension system, frame and FEM analysis and the first test results.
The Electron Ion Collider (EIC) Hadron Storage Ring (HSR) will reuse most of the existing superconducting magnets from the RHIC storage ring. However, for some sectors of the machine, a modification of the accelerators optics will be required. To do this, the existing RHIC magnet electrical circuits will have to be modified and some superconducting current leads will need to be used at higher current. A work was initiated to understand the current leads design parameters and their operational flexibility around these parameters, in particular for use at higher current.
This paper details the study of the existing RHIC current leads, their potential for use at higher current and where required the modifications to extend their operational range.
In this paper, the results of a nitrogen-based pulsating heat pipe (PHP) with the ability to change the number of turns are presented. The experiment assembly consists of two identical PHP subsections with their own fill lines. The condenser, the adiabatic section, and the evaporator section of each PHP are 90mm, 1000mm, and 60mm respectively. Because of the unique design of the condenser section of the PHP, it can change the configuration into 1-turn, 3-turn, 5-turn, and 7-turn PHP. The PHP was tested at the condenser temperatures 68.5 K, 77.3K, and 84.5K, which are below, at, and above the boiling point of the liquid nitrogen at ambient pressure. At each condenser temperature, the PHP was tested at three different initial fill ratios (38%, 50%, and 63%). The experimental results for the 1-turn and 3-turn setup of this nitrogen-based PHP assembly will be presented and analyzed in this paper.
Pulsating heat pipes (PHPs) are passive thermal management devices that, like traditional heat pipes, use thermally driven fluid flow and phase change to transfer heat efficiently. PHPs have been a subject of experimental research for a few decades due to their many potential applications, and improvements over the current state-of-the-art. However, many aspects of their operation are unknown, and their thermal performance is difficult to predict owing to stochastic fluid behavior and the numerous interdependent design and operating parameters. These issues are exacerbated for PHPs using cryogenic working fluids since PHP visualization experiments have yet to be realized at cryogenic temperatures, and due to the unique properties of cryogenic fluids, especially helium. Thus, PHPs using cryogenic working fluids such as nitrogen, neon, and helium have been prominent in recent experimental research. At the University of Wisconsin – Madison, an experimental test facility was constructed to accommodate long-distance helium pulsating heat pipe tests. As a result, 7-turn helium PHPs with adiabatic lengths of 1.25 m, 1.5 m, and 1.75 m have been tested, where their thermal performances have been analyzed as a function of adiabatic length, applied heat load, and fill ratio. Effective thermal conductivity values up to 350 kW/m-K have been achieved. Additionally, several adiabatic temperature and pressure measurements have shown fluid phase and flow behavior trends as functions of heat load and fill ratio. These experiments have shown that phase change in alternating adiabatic tubes can be linked to performance and flow regime changes.
Cryogenic pulsating heat pipes (PHP), also termed oscillating heat pipes, are passive thermal links that transfer heat by oscillatory motion of two-phase cryogen confined in serpentine-shaped capillary tubes. It is composed of three sections, namely, the condenser (cold sink), the evaporator (heat source) and the adiabatic part that can range from several centimetres to few metres. In spite of longer lengths, PHPs hold an advantage that their weight does not radically increase in comparison to counterparts like metallic thermal straps.
Comprehensive experimental investigation of cryogenic PHPs has been taken up at the Department of Accelerators, Cryogenics and Magnetism (DACM) within the Institute of Fundamental Research of the Universe (IRFU) at the French Alternative Energies and Atomic Energy Commission (CEA) Paris-Saclay centre. The aim is to present cryogenic PHPs as one of the potential thermal links aiding in distant cooling of superconducting devices from active cryocoolers. A 0.4 m long neon PHP with 1 mm capillary tube diameter has been recently developed characterized by one of the highest thermal conductance reported till date both in vertical and horizontal orientation.
An innovative modification in the construction of PHP evaporator is showcased in this article. This would considerably enhance the flexibility of PHPs in terms of their employment geometrically within the target application. Pilot experimental results for neon PHP coupled with the altered evaporator is presented for heat load up to 18 W. Additionally, its performance against that of a neon PHP with conventional evaporator is evaluated.
With the rapid progress of superconducting quantum computing, the cryogenic technology capable of providing appropriate cooling in the millikelvin temperature region is desirable. The cryogen-free dilution refrigerator featuring high reliability, long lifetime, and continuous cooling has become a promising cryocooler candidate.
As one of the key components of the dilution refrigerator, the orifice is used to control the flow and liquefy helium-3, which is crucial to achieving the millikelvin temperature. In order to analyze the dilution cycle and improve the refrigeration performance, a throttling model is established which focuses on the influence of complex physical properties of helium-3 and the dilution refrigeration cycle from supercritical pressure to saturation state. The effects of the diameters and thicknesses of the orifice on the flow rate are studied, and the influences of different inlet pressures and temperatures on the throttling process are discussed. The orifice throttling experiment is then conducted to verify the rationality of the model, and the results show that the simulation results agree with the experimental ones.
The theoretical analyses and experimental studies are described in detail, and the effects of the developed orifice on the performance of the dilution refrigerator will be presented and discussed. It is indicated that the throttling model can reasonably predict the flow rate under different structural, dimensional and operating conditions, and is helpful to the design and optimization of the cryogen-free dilution refrigerator.
Keywords: Dilution refrigerator; Helium-3; Throttling process; Liquefaction rate
The cryogen-free dilution refrigerator operating at around 10 mK or even below provides the indispensable cryogenic environment for the superconducting quantum computing, low-temperature transport property measurement and space exploration, etc. However, at extremely low temperatures, the Kapitza resistance often leads to a sharp deterioration of heat transfer in the heat exchanger and thus the sintered heat exchanger is necessary to optimize the interface heat transfer, which proves to be a crucial component of the cryogen-free dilution refrigerator. The design of the heat exchanger becomes particularly critical because its flow and heat transfer characteristics directly impact the cooling performance.
In this paper, a numerical model of the sintered heat exchanger is established to study the effects of particle size, porosity, and specific surface area of the powder on the heat transfer characteristics and the flow resistance under various working conditions as well. Based on the theoretical analysis, the structural and dimensional parameters of the sintered heat exchanger are optimized to meet the requirements of achieving cooling temperature below 10 mK for a He-3 flow rate of 100-300μmol/s. An improved sintered heat exchanger is then designed and integrated into the cryogen-free dilution refrigerator. The verification experiments are conducted and the results show a good agreement between simulations and experiments. The model can accurately predict the performance of the sintered heat exchanger and provide a helpful guidance for the optimization of the cryogen-free dilution refrigerator.
The theoretical analyses and experimental studies are described in detail, and the flow and heat transfer characteristics of the sintered heat exchanger are presented and discussed.
Keywords：Cryogen-free dilution refrigerator; Sintered heat exchanger; Heat transfer performance; Numerical analysis model; Experimental verification
The cryogen-free dilution refrigerator operating in the millikelvin temperature region has the advantages of no magnetic field interference, high reliability and long-term stability, which play an important role in providing the desirable cryogenic environment for the quantum computing. A cryogen-free dilution refrigerator generally operates over a broad range of temperatures, yet the large temperature difference between the precooling stage and the dilution unit may lead to serious heat leakage which would severely lower the cooling rate of cryogenic components. The gas-gap heat switches (GGHS) featuring high conductance and high switching ratio can control the thermal conductance between stages in the refrigerator and then accelerate the precooling. Furthermore, the GGHS can be designed without any moving part and thus significantly simplify the operation.
This paper presents the design of a passive GGHS which consists of multiple inter-leaved fins made of low-emissivity gold-plated coppers. The ON state is realized by introducing Helium into a gap between two conductors to provide the high thermal transfer, while the OFF state is achieved by removing the exchanging gas helium. An analysis model is established to optimize the switch geometry and discuss the effect of the cross section of fins. The switches with rectangular and triangular fins are modeled separately to value the thermal conductance, and the simulated results show that both switches can achieve the ratio of "on" to "off" conductance of greater than $10^4$.
The experiments are then conducted to verify the theoretical analyses. It is found that the cross section of fins slightly affects the witching ratio, while narrowing the gas gap or enlarging the surface areas can greatly improve the switch heat transfer. The important parameters such as switching times and thermalization of the sorption pump are also focused on. A good agreement between theoretical analyses and experimental results are observed.
Thermoacoustic machines depend on the complex relationship between thermodynamics and acoustics, and thus understanding it is vital in order to analyse the working principles and optimise parameters (i.e. geometrical or operational) to improve their performance. This paper investigates how numerical modelling can be used to explore this relationship and compares the accuracy of the performance predictions for different numerical simulation software. The software used included one designed for modelling Stirling machines called ‘Sage’ and one designed for modelling thermoacoustic machines called ‘DeltaEC’. To compare their results a model of both a thermoacoustic Stirling engine and refrigerator were developed from existing models in published papers, which contained experimental data to validate the numerical models. The results from the thermoacoustic Stirling engine model show that there is good agreement between the predictions from DeltaEC and the experimental data, as well as relatively good agreement between the Sage and DeltaEC predictions. However, due to Sage requiring a different approach to model the boundary conditions for the standing wave type machine (i.e. one end closed) the predictions varied slightly from those by DeltaEC. The results from the thermoacoustic Stirling refrigerator model, however, show improved agreement between the predictions from Sage and DeltaEC – potentially due to Sage and DeltaEC using a similar approach to model the boundary conditions for the travelling wave type (i.e. two open ends). Overall, it was found that although both can accurately model travelling wave thermoacoustic machines, the nature of Sage’s solving method makes it more complex to model the standing wave type compared to DeltaEC. A discussion on the use of numerical models as a tool for better understanding thermoacoustic machines, and the importance of the accuracy of the results to allow for optimisation and improvement in their design is presented.
Topics: Thermodynamic & Acoustic modelling
Keywords: Thermoacoustics, standing wave, travelling wave, modelling, Sage, DeltaEC, Stirling, stack, regenerator
The Cryogenic Flux Capacitor (CFC) is a cold, dense energy storage core that is being studied in the cryo-compressed, about 300 bar and 80K, region of gaseous hydrogen (GH2) storage and liquid hydrogen (LH2) region near the normal boiling point. The hydrogens storage is improved by physically bonding the molecules within the nanoscale pores of the aerogel composite blanket material. The process of bonding or debonding is governed by principles of physical adsorption (physisorption) and thermodynamics. The large surface area afforded by the nanoporous aerogel (~1,000 m2/g) allows its storage performance to easily exceed capacities of high-pressure GH2 storage for an equivalent volume. With the integrated aerogel, subscale tests have shown that storage is increased by about 49% over a simple tank filled with GH2 at the same operating temperature and pressure. For LH2 conditions, the CFC is shown to operate at equivalent densities.
For the techno-economic analysis (TEA), the source of hydrogen is compared between onsite steam methane reforming (SMR) and onsite solar photovoltaic (PV) panels providing power to electrolyzers to produce GH2. The TEA compares pure hydrogen burning in a combined cycle gas turbine (CCGT) to hydrogen fuel cells with an overall net power output of 650 MW. The SMR system uses natural gas as an input and includes a carbon capture and storage (CCS) system. The levelized cost of electricity is developed based on the capital cost and operating cost of the systems. Sensitivities are discussed around the cost of natural gas, ranging from 1.93 USD per MMBTU to 6.75 USD per MMBTU, and carbon dioxide disposal, ranging from 7 USD per tonne to 10 USD per tonne. For comparison to the conventional CCGT baseline, a baseload scenario is adopted with 85% capacity factor.
The results of the study show that onsite hydrogen generation from SMR is about 1 to 3 USD per kg over the life of the plant and the PV hydrogen production produces at 4 to 5 USD per kg. The cost of storage for CFC is compared to other systems, including high-pressure GH2 and atmospheric LH2. The system is shown to provide the lowest costs for all these options at the grid scale, due to its higher capacity than high-pressure GH2 and ability to operate at 80K, receiving refrigeration from liquid nitrogen systems reducing capital and operating costs when compared LH2 storage systems. SMR is competitive with CCGT at the gas prices, both of which have lower LCOE than the PV system. When accounting for variability in gas prices, the PV and electrolyzer system is less sensitive to these changes and provides the lowest LCOE across the whole range.
The abundance and diversity of end-use applications for hydrogen necessitates continued and accelerated research into advanced storage technologies. Traditionally, hydrogen has been stored in one of two ways: as a high-pressure, warm gas; or a low-pressure, cryogenic liquid. Methods such as cryo-supercritical (i.e. cryo-compressed) and cryo-adsorbed have also been explored, but are not yet mainstream. Cryo-adsorbed is attractive in that, depending on the adsorbent and storage conditions, higher storage densities at higher temperatures than liquid can be achieved. Recently NASA, in partnership with Eta Space, Southwest Research Institute, the University of Central Florida, and Air Liquide, have been exploring the use of inexpensive, commercially available silica aerogel blanket materials in cryo-adsorbed hydrogen storage applications. Unlike most adsorbents, aerogel blanket is not a powder, but a robust, composite material that can be formed into a variety of shapes to aid in more efficient storage system designs, and has already been proven to uptake large quantities of other fluids such as nitrogen and oxygen. Recent experimental efforts into the uptake of low-pressure hydrogen gas in aerogel blanket at 77 K, and liquid hydrogen at its normal boiling point will be discussed. Although preliminary in nature, the results of these tests are promising, showing up to a 49% increase in storage density at 77 K over the gas alone, and when brought to normal boiling point conditions, tests show a one-to-one volume equivalency with LH2.
Energy from hydrogen is an appropriate technological choice in the context of sustainable development and for a future CO2-neutral society. Within the framework of the national hydrogen lead projects, Karlsruhe Institute of Technology (KIT) is working with project partners of the technology platform "TransHyDE" in the lead project "AppLHy!" on the transport and application of liquid hydrogen (LH2). LH2 offers important advantages like its high purity, high energy density, storage at low pressure and the provision of a cryogenic temperature level that can be feasible for implementation in transportation applications.
Although austenitic steels have been implemented in LH2 direct contact for decades now, detailed microstructural and mechanical studies are still missing for 20 K/ that low temperature regime. With an austenitic LH2 vessel that has been in long-term condition with H2 exposure in the cryogenic regime as study model, a comprehensive study of the influence of gaseous H2 and LH2 on the micro and macro properties of the vessel were carried out. For a complete study and verification of the well-equipped H2 & LH2 facilities at KIT, a second short-term hydrogen exposure on the vessel has been carried out.
Within this contribution, the long-term results as well as the short-term exposure will be presented and discussed.
There is rapidly growing interest in the aviation sector for the use of liquid hydrogen (LH2) as a zero emissions fuel for commercial aircraft, with major OEMs committing to hydrogen aircraft by 2035. Currently metallic tanks are used to store the LH2, which are much heavier than those used for conventional fuels resulting in significantly reduced operational range and/or payloads. Hence, carbon fibre reinforced polymer (CFRP) composite tanks are being considered as an alternative to conventional metallic tanks due to predicted potential 40% weight savings. However, when CFRPs are cooled to cryogenic temperatures, internal stresses are developed as a result of the mismatch in coefficient of thermal expansion between the constituent materials. The internal stresses can lead to microcracking of the CFRP that reduce the mechanical performance of the tank and cause hydrogen permeation leading to tank failure.
Despite the importance of assessing the resistance of CFRPs to microcracking at cryogenic temperature, standardised tests procedures do not exist. The most common test involves thermally cycling CFRP coupons by repeated immersion in liquid nitrogen and inspection of the coupon edges using optical microscopy at ambient temperature between thermal cycles [1]. As the coupons are not subjected to mechanical loading, either during immersion or the inspection, the procedure is limited. Firstly, in-service the material will be subjected to additional loading, and more importantly when the inspection takes place at ambient temperature the microcracks can close and not be visible. A further challenge is that some highly toughened polymers do not crack until several hundred cycles or not crack at all without the introduction of additional load.
Microcrack Fracture Toughness (MFT) [2] provides an alternative to the repeated immersion procedure. The MFT test in [2] involved loading various cross-ply CFRP coupons in tension and observing the evolution of the microcracks in the 90o plies using optical microscopy. Images of the microcrack evolution were recorded alongside load and displacement from the test machine allowing a quantitative evaluation of microcrack density against applied load, from which the applied stress was calculated. In [2] an attempt was made to characterise the microcrack fracture toughness at cryogenic temperatures. During the tests the coupons were unloaded and imaged at ambient temperature, resulting in similar challenges to those associated with the closure of the microcracks as the immersion test procedure. Furthermore, the removal of the coupon from the test machine at predefined intervals and warming for inspection means the test is time consuming and costly.
In the present work, a novel in-situ microcrack measurement technique is developed to obtain the microcrack fracture toughness at cryogenic temperatures. In the new experimental set up, a bespoke cryostat is designed and manufactured using 3D printing. The cryostat enables observation of the transverse microcracking within the CFRP coupon during mechanical testing. A mixture of nitrogen gas and liquid is injected into the cryostat, facilitating local cooling of the coupon, which enables a more efficient and comprehensive testing campaign.
A range of CFRPs are evaluated for their microcracking resistance at both ambient and cryogenic temperature. This enables a comparison of the impact of temperature and thermal stress state on the materials microcracking behaviour. The same materials are also evaluated using the repeated immersion method. The results from MFT are then compared to the resistance to microcracking in the immersion tests.
Environmentally friendly aviation is one of the great challenges of this century. One promising approach is electric flight, in which an energy carrier (e.g. liquid Hydrogen LH2) and an electric powertrain work together. Within the scope of the joint project AdHyBau, the overarching goal is the development of new additive processes and fiber composite-metal hybrid designs for use in the cryogenic environment of such an electric propulsion system.
Additive manufacturing of complex components for use in the cryogenic temperature range down to 20K (LH2) is one essential component in the production. For the design and optimization of the different components it is necessary to know the thermo-physical behavior of such materials like high purity copper, Ti6Al4V alloy, Al-Mg-Sc alloy, and Inconell 718. The thermo-physical parameters investigated are thermal expansion, thermal & electrical conductivity and heat capacity. Further production-related influences coming from the method used (SLM, DED or coldspray) and orientational dependences are discussed.
Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904D.
The use of pure copper and Inconel 718 as cryogenic materials has been well known in the cryogenic materials space. Despite their potential, little is known about the use of these materials in cryogenic environments and their ability to withstand these conditions when manufactured using Additive Manufacturing (AM) methods. AM has emerged as a promising production method due to its ability to produce complex geometries and near net-shape parts. Copper being a highly conductive material for electrical applications and Inconel 718 as an engineering material both offer a widespread range of use cases in cryogenic applications.
In this paper, we demonstrate the Cold Gas Spraying (CGS) of copper and the Selective Laser Melting (SLM) of Inconel 718 as the AM processes of choice for each respective material. The main distinction between both processes is that CGS is useful for rapid deposition of material in the range of several kg/h whereas SLM is limited to a range of several hundred g/h. However, CGS can only yield bulk structures while SLM allows to produce intricate fine structures due to the nature of each processes’ approach.
The development of the CGS process has been a rapidly evolving field in recent years. The process involves the acceleration of metallic powders to high velocities, which are then deposited onto a substrate to create a dense, solid structure. Originally developed as a coating process, it has been used to fabricate a wide range of materials, including metals, ceramics, and intermetallics, and has proven to be a promising alternative to traditional manufacturing methods such as casting and welding.
One of the challenges in the field of cold spray has been the ability to produce bulk specimens of large height. This has limited the use of CGS to produce e.g. tensile specimens in build direction, which are critical for the characterization of material properties and for the validation of material models. In this work, we present the development of a CGS process that can produce bulk material of up to 160 mm height to obtain such specimens in build direction. The process was optimized through a series of experiments to achieve the desired material properties. The microstructure of the specimens was then characterized. The results showed that the CGS process was able to produce bulk specimens with a high degree of uniformity and with mechanical properties that are comparable to those of traditionally manufactured materials. We show how we overcame the boundaries of thin layer application to produce bulk material from many consecutive layers.
On the other hand, the SLM process involves the use of a laser beam to melt and solidify Inconel 718 powder layer-by-layer to create a solid part. In this process a powder bed is lowered after each consecutive layer and new powder applied on top of it. No process development was needed to be able to obtain specimens for material testing. However, an important aspect in question was the post SLM heat treatment for a material originally designed for operating in environments of elevated temperatures.
The results presented here give insight into how to tweak processes and/or post-processing to obtain materials from AM and make them usable in cryogenic environments.
Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904A.
The additive manufacturing (AM) of polymer matrix composites (PMCs) presents a unique option for reducing the mass of aerospace vehicles and thereby the cost required for launch. Also, there are many AM metal matrix composite (MMC) systems that can increase part efficiency and performance. These solutions have the potential to reduce the cost of terrestrial applications where cryogenic temperatures are present. Thus, this paper explores the mechanical characterization of these materials at 20K and the effect material deviations have on part mass and performance. To assert accurate data obtainment in all material characterization, the mechanical load frame utilized for mechanical data acquisition, the Cryogenic Accelerated Fatigue Tester (CRAFT), is first detailed herein. Next, a mechanical characterization of the additively manufactured AlSi10Mg alloy and an MMC alternative are obtained. Third, the mechanical performance of an additively manufactured PMC liquid hydrogen tank constituent is collected in addition to an analysis on the effect the processing parameters have on the mechanical behavior. These developments permitted the recommendation for alternative material and processing parameter selections that have the potential to reduce launch vehicle dry mass and improve application performance. Beyond the observed improvements detailed within this paper, the data acquired encourages further cryogenic design optimization through modifications made to material selection and development.
Titanium 6Al-4V is a highly desired material for use in space cryogenic applications; specifically structural applications where high strength-to-weight ratios are needed and thermal applications where thermal isolation is needed. Furthermore, components can be fabricated via 3D-printing using this material, which in addition to the cost and schedule savings is very beneficial in allowing parts to be made with geometries and features that are very difficult and sometimes impossible to fabricate via traditional machining methods. These newly possible geometries and features are used to increase the components’ structural integrity and thermal capabilities. Although the alloy is known to have good mechanical properties at room temperature, there is little known about this material’s mechanical properties at cryogenic temperature when 3D-printed. This testing investigates the mechanical properties of 3D-Printed Titanium 6Al-4V at cryogenic temperature through cryogenic mechanical tensile testing to failure and evaluation of the failed coupons. The elongation, yield strength, ultimate tensile strength, and break strength of the material is provided and analyzed here.
Many organizations are developing compact lightweight highly efficient rotating machines for airplane applications. These machines include permanent magnets for excitation and iron-core with and without superconducting windings. Air-core (no magnetic iron) machines have the potential to be most lightweight and efficient. Such machines can use superconductors for both DC excitation field coils and AC armature coils, which need conductors under development, like MgB2 and Bi2212. Since Liquid-hydrogen (LH2) available on a plane is being considered as a coolant, it becomes feasible to develop machines with AC armature coils made off conventional conductors like copper, aluminum, and high-conductivity aluminum.
This paper describes conceptual designs for a 3 MW, 4,500 RPM motor employing REBCO CORC conductor for the DC field coils and conventional conductor Litz cable for the AC armature coils cooled with available LH2 on the plane. Both rotor and stator coils are contained in separate cryostats. The DC excitation coils on the rotor are operated at 40 K to work successfully with brushless flux pump exciter. Likewise, stator AC coils are cooled with available LH2 for taking advantage of conventional conductors at cryogenic temperatures. Motor size, mass and losses are compared for stator windings employing copper, aluminum, and high-conductivity aluminum (Hyper-AL). Compared with copper and aluminum machines, the machine employing Hyper-AL has smaller size, mass and total losses.
Energy to Power Solutions (e2P) in collaboration with the Illinois Institute of Technology (IIT) is developing a new Superconducting Series-type Hybrid Circuit Breaker (SS-HCB) concept for dc fault protection. The Ss-HCB is fundamentally different from other prior-art hybrid circuit breakers (HCB) or solid-state circuit breakers (SSCB) in the literature. The SS-HCB conducts its primary load current through High Temperature Superconducting (HTS) wires instead of power semiconductor switches and curtails its fault current to near zero
throughout the entire opening process of a series mechanical switch.
It offers the low ON-resistance of the conventional mechanical contacts
for normal operation and μs-scale fault response, even faster
than the fast-acting SSCBs. A proof-of-concept SS-HCB prototype
experimentally demonstrates the interruption of a fault current of
30 A within 10 μs at a dc voltage of up 5000 V. The operating principle,
simulation, and experimental results are discussed in this paper.
Superconducting electrical machines have emerged as an enabling technology for electric propulsion applications, and there are several ongoing efforts to develop these machines. The NASA High-Efficiency Megawatt Motor (HEMM), Center for High-Efficiency Electrical Technologies for Aircraft (CHEETA), and Cryogen Free Ultra-High Field Superconducting Motor (CRUISE-motor) are at the forefront of superconducting electric propulsion motor development, and this paper provides an in-depth comparison of these machines.
The CHEETA motor is specifically designed for use in a hydrogen-powered electric aircraft. It is a fully superconducting electric machine with a power output of 2.5 MW and a specific power greater than 25 kW/kg, achieving an impressive efficiency of 99.9%. To take advantage of the available liquid hydrogen, the machine is designed to be cooled by the hydrogen flow to the fuel cells.
NASA's HEMM is a partially superconducting motor with an HTS field winding and copper armature winding. It is a 1.4 MW electric machine that aims to achieve a specific power of 16 kW/kg with 99% efficiency. To cool the field windings, a rotating cryocooler is integrated with the rotor, which eliminates the need for external cooling to the rotor.
Hinetics is developing a Cryogen Free Ultra-High Field Superconducting Motor (CRUISE-motor) for large-scale electric airplanes. The aim is to develop a 10-MW partially SC electric machine with a specific power of 40 kW/kg and 99.4% efficiency. The machine features an integrated cryocooler on the rotor that provides cooling to the field windings. It also has a novel spork-supported rotor architecture that eliminates the conduction heat from the torque tube, minimizing the cooling load on the cryocooler. The air-core stator with exceptional thermal performance results in a modest armature temperature. These features enable Hinetics to develop a practical partially SC machine for electric propulsion applications.
This paper presents a detailed comparison of the key performance metrics of these three machines and provides updates on their development and testing. In addition to this, the full paper includes EM optimization, EM analysis, mechanical design and analysis, thermal analysis, and updates on risk reduction experiments of the CHEETA and CRUISE motors.
Many Free Electron Lasers (FEL) are nowadays based on linear superconducting accelerators (linacs). The typical layout of such a linac consists of a number of cryomodules (CMs) arranged in strings. Each cryogenic circuit in a string is protected by safety valves (SVs) in case of failure of the system or a catastrophic event. A typical worst-case scenario considers the venting of the insulation vacuum, causing a fast and uncontrolled warm up of the cryogenic circuits. Such venting can for example take place across a pump port belonging to a string. The amount of heat deposited on each circuit is a very important parameter to correctly size the safety devices.
This paper describes the tests performed at DESY on an EuXFEL cryomodule to evaluate the heat input to the three cryogenic circuits of the CM while venting the insulation vacuum. Test results are given with a particular focus of their application to long strings.
Back in 2018, LHC completed its run 2 physics period. Consolidation, maintenance, and upgrade activities performed during the subsequent long shutdown 2 period (LS2), based on a data-driven approach, allowed for full potential availability of the LHC cryogenics infrastructure before tackling the 2021 magnet quench training campaign, preparing the whole machine for operation at the increased energy of 6.8 TeV.
This paper will first give a summary of the main upgrades, consolidations and maintenance performed during the LS2. Magnet training of the machine to the increased energy of 6.8 TeV will be addressed. Results of the first year (2022) of run 3 physics will be presented, achieving high cryogenic availability in a heavily sustained operational context of the accelerator (beams energy increase, induced heat load, peak & integrated luminosity). Helium inventory management aspects will be discussed, with a particular highlight on the necessary operational adjustments taken to cope with the present supply market evolution. Implementation of several operational modes for cryogenic plants will be presented, towards significant power savings while maintaining nominal physics production at the highest availability rate.
RAON, Rare isotope Accelerator complex for ON-line experiments, is the first superconducting linear accelerators in S. Korea. It will have three linear accelerators (LINAC), SCL1, SCL2, and SCL3. Now, construction of the SCL3, the third superconducting LINAC was finished in the middle of 2022 and the commissioning of its cryogenic system was done July, 2022. The first cooldown of the LINAC with the cryogenic system was started from September, 2022 and their temperature was reached at 2.05 K in January, 2023. The first cooldown was successfully completed and the static and dynamic heat loads of the LINAC were measured. This paper shows the results of the first cooldown and the heat load tests.
At the European Spallation Source (ESS), a 5 MW beam of 2.0 GeV proton with a nominal current of 62.5 mA driven by an accelerator will strike a tungsten wheel target at a repetition of 14 Hz and a pulse length of 2.86 ms. The fast neutrons produced via spallation process are reduced to cold and thermal neutrons of a lower energy level by passing through a thermal water pre-moderator, and up to four liquid hydrogen moderators. At the beginning, the ESS will install two hydrogen moderators above the target wheel and plans to replace them by four ones above and below the target in the future. The calculated nuclear heating is 6.7 kW for the proton beam power of 5 MW, while that for the four moderators is 17.2 kW. A cryogenic moderator system (CMS) has been designed to continuously supply subcooled liquid hydrogen with a temperature of 17 K and a parahydrogen fraction of more than 99.5% to each moderator placed in parallel at the flow rate of more than 240 g/s in order to maintain an average temperature rise at the moderator within 3 K. For the 5-MW proton beams, the total heat load is 21.9 kW, which includes a static load of 4.6 kW. The heat load is removed by a large-scale 20 K helium refrigeration plant, which is called the Target Moderator Cryoplant (TMCP), with a maximum cooling capacity of 30.3 kW at 15 K. Two compressors are operated at a discharge pressure of up to 2.2 MPa to deliver a high pressure helium stream to the CMS of up to 1125 g/s, operating all the three expansion turbines are operated. The TMCP cooling capacity will be controlled by the so-called floating pressure process. All the ESS helium cryoplants are co-located in order to facilitate maintenance and consolidate utilities like a helium recovery system and external purifier. Therefore, the HP helium stream is delivered from the TMCP cold box to a valve box close to the CMS cold box in the Target building through a 385 m-long vacuum insulated cryogenic helium transfer line (CTL). The valve box has functions to not only adjust the flow rate and the supply temperature to the CMS but also the return temperature to the TMCP cold box. The TMCP installation and commissioning plans are split into three phases. Phase 1 commissioning that comprised the compressor skids and the cold box alone has been finished in 2019. In the Phase 2, the 385 m-long CTL, the warm helium line and the valve box have been installed and integrated into the existing TMCP cold box in summer 2022. Subsequently, the TMCP commissioning has been conducted without connecting the CMS until December 2022. The performance evaluation tests such as the expansion turbines efficiency, the CTL pressure drop, the heat load and the cooling capacity have been conducted. We have studied how to operate in each operation mode such as a cooldown, warmup and beam injection modes in order to establish an automatic TMCP-CMS control system. Furthermore, safety functions as an instrument air failure have also been tested. The final phase of the installation, where the CMS cold box will be integrated, is planned in 2023. This paper will describe the performance test results and the safety function test conducted in the Phase 2 TMCP commissioning.
SLAC National Accelerator Laboratory has upgraded to LCLS-II, featuring a 4 GeV superconducting linear accelerator composed of 37 cryomodules and two large helium refrigeration systems with a cooling capacity of 4 kW at 2.0 K. The LCLS-II Helium Refrigeration System (HRS) consists of two compressor stations, each with a power of approximately 4.5 MW, two 4.5 K cold boxes, each with a power of 18 kW equivalent at 4.5 K, and two sets of cold compressors that can each produce a flow of 230 g/s at 31 mbar (2.0K). Performance tests of the HRS were meticulously planned and successfully carried out, with results demonstrating that it exceeded the process requirements for LCLS-II operations. This paper provides a detailed presentation of the LCLS-II HRS performance and the challenges encountered during the commissioning phase.
SLAC National Accelerator Laboratory has upgraded to LCLS-II, featuring a 4 GeV superconducting linear accelerator composed of 37 cryomodules and two large helium refrigeration systems with a cooling capacity of 4 kW at 2.0 K. LCLS-II linear accelerator was successfully cooled from ambient temperature to 4.5 K and then to its final operating temperature of 2.0 K (31 mbar). In this paper, we describe the cool-down strategy, provide details of the 2.0 K pump-down results, and discuss the challenges faced during commissioning.
GTL is currently developing and validating a series of ultra-lightweight composite dewar tanks for liquid hydrogen (LH2) powered aircraft. These all-composite, vacuum-jacketed, dewar-tanks can achieve hydrogen weight fractions in the 60% to 80% range including composite dewar shell, multilayer insulation, and inner tank, which allows them to carry 10 times the hydrogen as conventional hydrogen storage systems. This performance breakthrough offers the means to revolutionize the aviation industry with extended range, reduced operating cost, and elimination of carbon emissions.
GTL has fabricated two developmental prototype composite dewar-tanks and is testing them with liquid hydrogen. This paper will summarize the LH2 testing of these prototypes. The paper will also describe the development of GTL’s in-house LH2 test capability and related test systems.
It is important to understand the thermal hydraulic behavior of liquid hydrogen (LH2) inside the tank under static and dynamic conditions for developing an LH2 tank on a car and a boat. As fundamental studies on pressure accumulation inside an LH2 tank, the temperature, pressure, and level of LH2 has been measured under a static condition in terms of initial filling ratio dependence, using a 20 L tank. It is found that the pressure rising rate shows relatively high value just after beginning of pressure accumulation and the accumulation time indicates relatively short value in the case of high filling ratio. Experimental results of the time variation of pressure are compared with calculation results based on homogeneous self-pressurization condition.
The need to decrease the gross weight of cryogenic hydrogen fuel systems in future zero emission mobility leads to increasing activities in the field of cryogenic lightweight engineering. Fibre reinforced thermoplastic composite materials (FRT) are considered for cryogenic applications despite their bias towards permeation. However, permeation through plastic materials is of major concern in cryogenic applications. Even tiny fluxes can very much compromise the insulating power of high vacuum spaces required for insulation of cryogenic systems such as tank structures or transfer lines. Hence, it is essential to qualify those FRT in terms of their hydrogen permeability for future usage in mobile cryogenic applications. The conventional concepts for measuring permeability in plastic materials are not sufficient for cryogenic measurements of FRT as shown in a previous paper. Therefore, a novel laboratory test rig concept was proposed. In this paper, we validate this concept and show its eligibility for measuring permeation of hydrogen through plastic materials under cryogenic conditions. Furthermore, we show first results of (cryogenic) hydrogen and helium permeation through fluorocarbon polymers like PTFE.
Liquid hydrogen (LH2) aircraft developments are highly dependent on the hydrogen tankage as well as the insulation system requirements. Recently, Georgia Tech investigators, as part of a NASA preliminary evaluation activity, have been developing a single-aisle LH2 passenger jet to better understand the sensitivities that hydrogen puts onto the aircraft as a system. As a part of the activity, NASA and Georgia Tech developed the ability to integrate a tank set into the aircraft including insulation systems. Several key observations were made on the insulation system requirements that were driven by the observation of the system-level operations. Aircraft were evaluated with the assumption of constant tank pressure control. Assessments were made on several insulation system options to avoid venting of hydrogen during nominal and worst-case hot-day flights. Additional evaluations were performed based on ground profiles. The insulation solutions were then implemented in the Georgia Tech flight simulation software and simulations of the aircraft missions were performed verifying that minimal venting of the aircraft occurred pre-takeoff with no venting during flight.
Extracting liquid from hydrogen storage vessels require the maintenance of pressure in the ullage space to ensure uniform flow to a consumer. Due to the large change in volume during vaporization of liquid hydrogen, a percentage of flow is diverted from the consumer for pressure maintenance back into the tank. The return state of the hydrogen should be close to saturated vapor at comparable volumetric flow rates for liquid extraction and smooth operation. This paper details the theory, design, and experimental performance of a liquid hydrogen pressurization system. A cartridge heater, throttle, and manual valve are utilized to vaporize, reduce pressure and pressure oscillations, and control flow. Experimental measurements are compared with theoretical predictions for liquid nitrogen and liquid hydrogen flows. The end results demonstrate the performance of the heater and throttle for pressure maintenance of a liquid hydrogen tank.
In order to establish a “hydrogen-based society” for carbon-neutral, Japanese and Australian governments promoting the project of “International liquefied hydrogen supply chain”. In this project, huge amount of LH2 made from brown coal in Australia will be transported by marine ship. GH2 is liquified by renewable energy, and the LH2 is load on the cargo ship and transported to Japan.
As a pilot project, the world’s first LH2 tanker, “Suiso Frontier” was developed and successfully transported LH2 from Australia to Japan in 2022. The LH2 tank on the ship is a pressure accumulation type, having 1,250 m3 in volume. During the shipment of LH2 for 3 weeks, the pressure and Temperature inside the tank are gradually increased due to the accumulation of heat input. The LH2 is pressurized by GH2, that is, a gas-liquid two-phase system of single specie. Then, when the ship arrives at Japan, the pressure of LH2 must be decreased before the unloading from the ship, called the operation of “depressurization”.
In the depressurizing operation, the decreasing speed is quite important. Of course, the decreasing speed can be controlled by careful operation of valve opening. However, due to a wrong operation of valves, or in case of emergency release of pressure, there remains the possibility that the decreasing speed come to be too rapid, which should cause an explosive boiling or a geysering phenomenon in the tank. At the same time, the liquid surface should lifted up to the top wall of the tank.
Related to such a rapid depressurization, we had conducted experiments with small vessel containing LN2 or LH2. There are many experimental data and predictive methodology of CFD for a small vessel, however, we must predict what is happened, or what is NOT happened in a real scale tank having 1-million times larger in volume than the small vessel in laboratory scale.
To establish the predictive methodology, thermo-fluid characteristics in large scale tank are strongly desired. In this paper, by use of a LH2 tank of 30m2 as an infrastructure for rocket propulsion research, depressurization process was experimentally investigated. Owing to heat exchanger and valves connected to the LH2 tank, the initial distribution of temperature in vertical direction could be changed. When the liquid was occupied by sub-cooled LH2, the pressure would decrease adiabatically and rapidly w/o boiling. In the other case, when the liquid was occupied by saturated LH2, the pressure would decrease slowly with boiling. This was because the flow rate of exhaust gas and generating rate of boiling gas was almost balanced. In the cases with saturated LH2 with higher liquid level, it was observed that adiabatic depressurization followed by pressure recovering. The flow field inside the tank could not be visualized, however, explosive boiling in super-heated liquid was seemed to be induced.
The flow field was also investigated numerically by use of original CFD code developed in the University of Tokyo. The pressure recovery was well reproduced in CFD and the corresponding boiling was also calculated.
Different from experiments, we can impose a hazardous and dangerous conditions in numerical simulations. We will use the CFD as the strong tool of cryogenic fluid management, not only for the understanding real behavior, but also evaluating hazard analysis.
Safe and efficient liquefaction of cryogenic propellants is critical to future Moon and Mars missions for NASA. There is a need to liquefy, store, and transport cryogenic fluids at temperatures that minimize liquid boil-off. A low-cost, low-SWaP (size, weight, and power) instrumentation suite to measure thermal response is critical to validating models and maturing liquefaction technologies. This presentation will discuss the fabrication, deployment, and experimental results of an array of enhanced fiber sensors, based on optical frequency domain reflectometry (OFDR), installed alongside co-locating silicon diode rake from NASA CryoFILL (Cryogenic Fluid In-situ Liquefaction for Landers) testing during 2022. Measurement data and measurement accuracy with respect to co-locating silicon diodes will be discussed in detail, and future work will be presented.
SLAC National Accelerator Laboratory has upgraded to LCLS-II, featuring a 4 GeV superconducting linear accelerator composed of 37 cryomodules and two large helium refrigeration systems with a cooling capacity of 4 kW at 2.0 K. In this paper, we provide an overview of the instrumentation and controls for the Cryoplant, Cryodistribution, and Cryomodules, spanning from the instruments themselves, to the PLC I/O cards, and finally to the Human-Machine Interface (HMI). We also discuss the best practices and lessons learned during the commissioning process, which contributed to the successful implementation of the instrumentation and controls.
SLAC National Accelerator Laboratory has upgraded to LCLS-II, featuring a 4 GeV superconducting linear accelerator composed of 37 cryomodules and two large helium refrigeration systems with a cooling capacity of 4 kW at 2.0 K. This paper focuses on the Helium Refrigeration System (HRS) controls and automation. It presents the various automated functions, sequences, control logics and machine protections embedded in the system. It highlights how the automation simplifies and streamlines the operation of the LCLS-II HRS.
Cryogenic fluid flow is a critical measurement parameter but is difficult to properly measure due to the extreme environmental conditions and the frequent presence of multiphase flow during saturated liquid transfers. Multiphase flow proves challenging for most flow measurement methodologies; furthermore, additional measurements of volume fraction, quality, and slip velocity are often required. In-line capacitance based sensors have the potential to overcome these limitations. In this paper, a capacitance sensor in a multiphase cryogenic flow loop is evaluated for its ability to measure liquid volume fraction, gas phase velocity, and total mass flow rate for two-phase cryogenic nitrogen flow.
The Coriolis mass flowmeter (CMF) has the advantages of a simple structure and high measurement precision. Compared with liquid nitrogen (LN2) and water, the density of liquid hydrogen (LH2) is more than one order of magnitude smaller, which leads to significantly different flow-induced vibration (FIV) characteristics in the CMF. The fluid-structure interaction (FSI) theory model for the U tube CMF was established based on the Euler beam theory in this research, and the FSI numerical simulation was conducted to solve the effect of fluid flow. The difference in measurement characteristics of CMF for LN2 and LH2 was revealed and the optimized measuring tube structure was proposed. The theory and numerical model are first validated by comparing the experimental results from the published research. Then the results of structural frequency, phase difference, and time lag for LH2 are compared with those for LN2, and the effect of flow velocity, the position of sensors, and the geometry of the tube are studied. Results show that the time lag of LH2 is an order of magnitude smaller than that for LN2. Errors of -6.84% and 0.63% will be generated if the mass flow rate of LH2 is measured with CMF calibrated with water and LN2, respectively. The effect of the position of sensors on measured time lag cannot be ignored, which the time lag can be increased by 93% as the position of sensors variate. Time lag can be increased by 115% based on the optimization of the tube structure. The results reveal the FSI characteristics of the U-tube CMF with LH2.
The ETpathfinder (ETPF) is a reduced-scale prototype of the the Einstein Telescope Gravitational Wave observatory aimed at testing and advancing the required technologies. ETPF will have two Fabry-Perot Michelson Interferometer (FPMI) arms of which the mirrors are cryogenically cooled. Both are cooled by LN2 whereas one of the two has to be cooled further down to about 10 K by an additional cooling system. The high precision measurements of the third-generation laser-interferometry detectors in ETPF demand a cooling system with minimal vibrations during measurement phases. The University of Twente has proposed a modular cryochain design using a combination of sorption compressors and J-T cold stages. The design features a parallel cascade of 40 K neon, 15 K hydrogen, and 8 K helium stages, with cooling powers of 2.5 W, 0.5 W and 0.05 W, respectively. The compressor cells are cooled by a 70 K pumped liquid-nitrogen reservoir and the overall compressor input is 364 W. Because of the absence of mechanically moving parts, this cooler type has a minimum level of vibrations. The requirement in ETPF is that at the 8 K cold-tip the cooler vibration level should not exceed that of the seismic background at the ETPF site. In the most important bandwidth (2 - 20 Hz) the environmental vibration level is 30 nm pp (ASD = 4 nm/Hz). In parallel to the 10 K sorption-based cooler development, an ETPF Cryogenic Test Facility is currently realized at the University of Twente. Here, all cryogenic technologies and operating procedures for ETPF will be tested. The proposed sorption-based cryochain and the overall ETPF cooling system design will be presented, along with details on the upcoming testing and experiments.
The Einstein Telescope (ET) is a planned third-generation gravitational-wave detector that includes a low-frequency (LF) and a high-frequency (HF) laser interferometer. Cryogenic operation of ET-LF is imperative for exploiting the full scientific potential of ET, with mirrors operated at temperatures of 10 K to 20 K in order to reduce the thermal noise. Thermal shielding around the optics is essential to support the cool-down process and to decrease the heat load. Additionally in steady-state operation, mechanical vibrations must be kept to an absolute minimum in order to limit noise contributions from scattered light. We present a cooling concept for a thermal shield surrounding the cryogenic optics of ET-LF which considers rapid cool-down and low vibration in steady-state operation. During cool-down, cooling tubes enable the flow of supercritical helium, driving the shield temperature decrease by forced convection. For steady-state operation, the shield cooling mechanism is converted to static heat conduction in He-II within the same tubes. A first mechanical model is presented that fulfills the thermal and vibrational requirements. Thermal characteristics of the shield are demonstrated by means of analytical and numerical modeling results. Modal and dynamic analyses are performed to obtain natural frequencies and transfer functions.
The Einstein Telescope (ET) is a third generation gravitational wave detector,combining a low-frequency (LF) and a high-frequency (HF) laser interferometer. Cryogenic operation of ET-LF in the temperature range of 10 K to 20 K is essential to suppress the suspension thermal noise, which dominates the detection sensitivity at frequencies below 10 Hz. This requires suspension materials with high thermal conductivity and low mechanical dissipation at cryogenic temperatures. Two possible suspension concepts are currently considered, using either monocrystalline suspension fibers made of silicon or sapphire, or titanium suspension tubes filled with static He-II. The dissipative behavior of these suspensions is characterized by the mechanical Q-factor. It can be measured by the ring-down method, exciting the suspensions to resonance vibrations on the nanometer scale and analyzing the decay time. For this purpose, a new cryogenic test facility is being planned, allowing the investigation of cryogenic payload suspensions for third-generation gravitational wave detectors. The test cryostat is equipped with a cryocooler and enables real-size studies with various suspension materials and geometries. The future integration of He-II is foreseen to enable He-II filled suspension studies. We describe the scope of experiments and the conceptual design of the test cryostat.
The SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) is an all-sky spectral survey in a sun-synchronous low earth orbit. It measures spectrum in the near infrared band from 0.75um to 5um. To achieve this wavelength coverage, the instrument has two focal plane arrays, both passively cooled at <55K (mid-wave infrared) and <80K (short-wave infrared). Additionally, the instrument requires no moving parts for spectral resolution, relying instead on spacecraft-controlled pointing. A thermally isolating structure and a set of V-grooves reduce the heat flow conducted and radiated from the spacecraft bus. The thermal system also blocks the incident solar flux and earth radiation from reaching the sensitive cryogenic instrument while still allowing substantial pointing flexibility. The combination of passive cryogenic cooling and survey requirements in a sun exposed low earth orbit environment presents a challenge for the thermal design. This paper will discuss the SPHEREx payload overall thermal architecture, bounding thermal environments, the component thermal and thermo-optical properties, design trades and sensitivities, and analysis of on flight performance.
The Lunar Trailblazer (LTB) Mission consists of a spacecraft that hosts two science instruments, the High-resolution Volatiles and Minerals Moon Mapper (HVM3) and the Lunar Thermal Mapper. Flight system delivery is scheduled for the end of 2022. The purpose of the mission is to understand the form, abundance and distribution of water on the Moon as well as the lunar water cycle. HVM3 is a pushbroom shortwave infrared (SWIR) Offner imaging spectrometer that is optimized for the detection of volatiles to map OH, bound H2O and water ice. It has a spatial resolution of 70 m/pixel over a 20 km swath width and a spectral resolution of 10 nm over a spectral range of 0.6 to 3.6 µm. The spacecraft will deploy from an ESPA Grande and enter a 100±30 km lunar polar orbit where it may operate over all beta angles. The HVM3 thermal control architecture consists of active and passive elements. It leverages the passive cryogenic cooler design developed for the Moon Minerology Mapper (M3) that underwent a similar orbit. The first stage of the passive cooler is used to reject the heat of a Lockheed Martin Micro1-2 cryocooler that is used to cool the focal plane array (FPA). The second stage of the passive cooler is used to passively cool the optics. An overview of the overall thermal control design approach is presented.
We are ongoing R&D of ultra-fine MgB2 superconducting wires having a very small diameter much less than a human hair. These ultra-fine MgB2 wires could be bundled and fabricated easily into stranded cables for increasing the current capacity. In principle, the bending strain decreases with decreasing the wire diameter as well as the hysteresis loss. The stranded cables made by these ultra-fine MgB2 wires would have very flexible mechanical performance and thus react and wind techniques would be applicable. In addition, the coupling loss for the stranded cables is expected to be minimized by increasing the surface and contact resistance, which are relatively easy to be controlled. Therefore, it may be solved both the issues of mechanical brittleness and AC losses at once. The critical current density should be maintained to be comparable or more with commercial MgB2 monolith wires even through ultrafine wires and cables. The critical current and critical current density at 4.2 K of MgB2 ultrafine superconducting wires and cables will be presented.
In this paper Hyper Tech Research will report on the development of magnesium diboride superconductor wires and cables including 1st generation, 2nd generation conductors and conductors with significantly lower AC losses. We will show that present day MgB2 conductors are usable for DC and AC applications such SMES, motors and generators. Superconducting and mechanical properties of strands and cables will be discussed in addition to loss values and strand/cable architecture.
Because of the tape architecture of the REBCO coated conductors (CCs), it is crucial to grasp the size of the tape width and its variation along the length for the design of magnets or coils. Geometrical size can be measured relatively easily by such techniques as laser microscopy or optical microscopy, however, the electromagnetic tape width, at where the superconducting current can flow, is not well characterized so far. It should be relevant for understanding the influence of shielding current due to magnetization of the tape strands. It has been also pointed out that the quality of the tape edge is crucial for the reliability of coiling, i.e., micro-crack formation as a result of slitting may cause deterioration of the magnet due to high strain during the operation. The electromagnetic tape width can be a good indicator for the evaluation of the quality of the tape edges after slitting. In this study, we will describe electromagnetic tape width of commercially available long REBCO CCs based on reel-to-reel scanning Hall probe magnetic microscopy [1]. Thanks to its high spatial resolution along the tape width not only along the longitudinal direction, it allows us to evaluate electromagnetic tape width continuously as a function of longitudinal position. This is very unique data on the electromagnetic characteristic of long REBCO CCs.
Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP19H05617.
[1] K. Higashikawa, K. Katahira, K. Okumura, K. Shiohara, M. Inoue, T. Kiss, Y. Shingai, M. Konishi, K. Ohmatsu, M. Yoshizumi, T. Izumi, “Lateral Distribution of Critical Current Density in Coated Conductors Slit by Different Cutting Methods”, IEEE Trans. Appl. Supercond., Vol. 23, No. 3, 6602704, 2013.06, DOI: 10.1109/TASC.2013.2238983
The development of ultrahigh power density rotating machines is a research priority identified by electric aircraft programs worldwide, including ARPA-E, NASA, Airbus, and many others. There are many high field DC and AC magnet applications of such wires. One of the most important building blocks for these applications is the electric wire conductors. A complete scan of the resistivity of these wires as a function of magnetic field and temperature is needed for a wide range of temperature from 5K to 150K, as machines are now being designed for these temperatures, e.g. cooled by liquid-H2, LN2, liquified-natural-gas (LNG), and even CO2 dry ice. This work will present the resistivity of electric wire conductors of interest, including 99.999+% Al hyperconductors, AlBe metal alloys, carbon-nanotube cables, and Al and Cu conductors with varying purity 99.5% to 99.99%, drawing tempers, and ultrafine diameters used in Litz cables. Properties are measured for a complete range of temperatures (2K to 300K) in increments of 2-10 K, and magnetic fields from 0-9T. A Quantum Design Physical Properties Measurement System (PPMS) is employed to obtain this data. Steps are taken to avoid heat generation during the measurement process. For ultrapure materials with very low resistance, longer time and repeated measurements were used to increase the signal-to-noise ratio.
Acknowledgments: Support by the Air Force Office of Scientific Research (AFOSR) LRIR # 18RQCOR100, and the Aerospace Systems Directorate (AFRL/RQ)
We present results on a set of REBCO coated conductor samples characterized for their in-field performance using Vibrating Sample Magnetometry (VSM) over temperatures and fields of 4.2-77 K and 0-14 T. All REBCO samples contain Artificial Pinning Centers (APC) in the form of BMO nanorods (BMO¬3¬, M = Zr, Hf). Principal component analysis of VSM will be presented, identifying the main modes of variability relative to the average performance. Correlation between in-field performance at different temperatures and fields is analyzed. This work has led to reel-to-reel in-field critical current measurement of long tapes up to 4 T at 65 – 77 K to determine the in-field critical current of the tapes at high fields at low temperatures.
This work was funded by award DE-SC0016220 from the U.S. Department of Energy, Office of Science – High Energy Physics.
Iron-based superconductors (IBS) are very promising candidates for high-field applications owning to their ultrahigh upper critical field (Hc2) and very small anisotropy. For such applications, it is essential to develop multifilamentary superconducting wires with high transport critical current density (Jc). Compared with the tape-sharped multifilamentary wires with high aspect ratio, round- or rectangular-shaped wires are more convenient for the design and fabrication of high-field solenoidal coils. At present, highly dense superconducting filaments can be achieved via hot isostatic press for IBS wires. However, due to the lack of grain texture, the IBS wires made by using the conventional power-in-tube method show much lower Jc than that of tapes. In this work, Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) 3-, 7- and 11-filament wires were developed with a tape-in-tube method. The wires consist of tape-shaped Ba-122 filament with improved grain alignment, showing a best transport Jc two times higher than that of the conventional power-in-tube wires, indicating that the tape-in-tube process provides a new and promising fabrication route of multifilamentary IBS wires for practical applications. The evolution of the transport Jc, n-values and filament homogeneity for the 3-, 7- and 11-filament wires is systematically investigated in connection of the grain texture, mass redistribution and interface effects. Through 3D x-ray tomographic reconstruction and electron probe micro-analyzer analysis, we found that the filament uniformity and chemical composition homogeneity for the Ba-122 wires can be greatly affected by the interface between the Ba-122 filament and Ag matrix.
The electronic, thermal and mechanical properties of graphene make it an intriguing choice for the contact material in hybrid Josephson junctions. Work over the past few years has shown that graphene can be used to make high-quality junctions that can be incorporated into devices such as SQUIDs, qubits and bolometers. For some applications there are open questions about the suitability of graphene junctions. In other applications, they have already brought significant improvements in performance. This talk will review recent work on the graphene Josephson junctions, including efforts to improve manufacturability and to explore applications that make use of their additional functionality.
Demand for data processing and computation has been rising dramatically since the invention of electronics. Increasing system-wide power efficiency will support sustainability and UN Strategic Development Goals 4, 7-9, and 11-15. Superconductor electronics are emerging in quantum sensing—for data collection and processing; quantum computing—including qubits, controls, and readout; and hybrid environments for high performance computing and artificial intelligence training. Amortizing cryocooling via intelligent choices of the right materials systems doing the right functions at the right temperatures to optimize the use of wall power for the entire system, especially in large systems, could create optimally efficient systems. This talk will explore options and encourage functional analysis and system design where cryocooler development engineers and superconductor electronics system engineers, both quantum and classical, work in concert targeting overall power efficiency.
Superconducting circuits are a leading platform for quantum sensing and computing applications. Materials science of these superconducting circuits is considered with increasing importance to increase sensing fidelities and qubit coherence times, thus directly affecting the advancement of quantum applications. The choice of the material and nanofabrication process for superconducting devices directly affects their performance, reliability and functionality. Appropriate fabrication and film growth techniques need to be developed to incorporate quality-factor engineered components. A recent publication [1] demonstrated that switching from Nb to Ta based devices improved coherence times by a factor of two or more. This results was attributed to the oxide formation and stoichiometry of α-phase Ta films which leads to fewer sources of noise with which the qubit can incoherently exchange energy. In this presentation, we provide an overview of the most recent advancements in material science in the field of superconducting quantum circuits along with the challenges that remain and possible future research directions that need to be investigated. We will also present our findings regarding sputtered Ta and ALD-deposited TaC_x N_(1-x) and their quality factors from spectroscopic measurements of fabricated microwave resonators at varying powers in mK temperatures. Finally we will explore the current limitations in the fabrication and measurement processes that need to be taken into consideration for scaling up quantum circuits
[1] Place, Alexander PM, et al. "New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds." Nature communications 12.1 (2021): 1779.
Recent advancements in superconducting materials combined with advanced cryogenics are enabling new class of quantum applications. Quantum applications will be dependent on modular platforms that can probe and manipulate matter at the nanoscale and at low temperatures and simpler to use and manage. These environments will be used to assemble, align, and analyze functional, organic or inorganic, nano‐ and microstructures, and to probe their structures, properties and dynamics, with potential applications in quantum technologies, nano based technologies, sensors and nano-electronics.
This contribution presents an overview of recent advancement in cryogenic systems for quantum information processing (QIP), quantum sensors, quantum measurements, quantum materials and low dimensional and 2D materials. The new systems are modular and compact in size and realized by exploiting the recent advances demonstrated in superconducting and cryogenic technologies. These new systems together with cryogen free technology, sample management and advanced instrumentation have opened a new era in quantum technologies.
APC Nb3Sn wires have been made which incorporate non-superconducting nanometer-scale inclusions in the form of ZrO2 or HfO2. In addition to strengthening the surface-type flux pinning by refining the grain size, the nanoparticles introduce a point-type pinning mechanism, the efficacy of which peaks at higher magnetic field than the grain boundary pinning. However, the size and spacing of the point pins is not uniform. While a particle is most effective at pinning when its radius is the same as the superconducting coherence length (~3.5 nm in Nb3Sn), the particles have a distribution of sizes which can be affected by heat treatment and strand composition. We evaluate the effect of changes to the size of the nanoparticles due to the choice of alloying element and heat treatment on the flux pinning. In addition, the interplay of coexistent surface and point pinning and the behavior as pin density approaches the fluxon spacing are considered.
In the past few years a new type of Nb3Sn strand with artificial pinning centers (APC) has demonstrated significantly superior performance relative to the state-of-the-art Nb3Sn conductors. Such APC strands are based on the internal oxidation method, which generates nano-size ZrO2 or HfO2 particles (mostly 1-10 nm) in Nb3Sn. It was found that this method improves high-field Jc via four mechanisms: (1) the particles directly serve as flux pinning centers (point pinners), (2) the particles refine Nb3Sn grain size, (3) the flux pinning force (Fp-B) curve peak shifts to higher fields, (4) the irreversible field (Birr) is enhanced. In 2019 the APC conductors we developed first reached the non-Cu Jc specification required by the 16 T dipole magnets for the proposed Future Circular Collider (FCC). Since then our efforts have been mainly focused on pushing the APC strands toward readiness for practical applications, and great progress has been made. In this talk a review of the APC Nb3Sn conductors will be given, including their opportunities, challenges, recent progress, and future plans.
Critical current density $J_c$ properties of 7 core Cu/Ag/(Ba, K)Fe$_2$As$_2$ (Cu/Ag/Ba122) tapes are investigated in low temperature and high magnetic field. The tape was fabricated by a powder-in-tube method with a flat-roll process [1]. The hysteresis behavior in magnetic field and its angular dependences of $J_c$ were observed at 4.2 K and low field. The $J_c$ values in increasing filed are smaller than those in decreasing field and upturn behaviors in field dependence of $J_c$ appear only in increasing field. These Jc hysteresis behaviors appear in all magnetic field angle at 4.2 K below 8 T although the hysteresis width decreases when the magnetic field angle approaches to $B$//c. The upturn behavior of field dependent $J_c$ in increasing field can be understood by Gurevich model based on the flux pinning of Abrikosov-Josephson vortices at grain boundaries [2]. The anomalous angular dependence of $J_c$, which shows a broad peak around B//c and a dip at $B$//ab, is observed at 4.2 K and low fields and it almost disappears at 18 T. These $J_c$ properties can be represented by the flux pining model by nano-scaled spherical pinning centers [3, 4]. Since no any additional inclusions are introduced as pinning centers in the Ba122 tapes, the strain induced nano-scaled spherical pinning centers are considered from TEM study. It is a key to improve $J_c$ in Ba122 tapes. The detail current transport mechanism and flux pinning will be discussed at the presentation.
[1] S. Liu $et$ $al.$, Supercond. Sci. Technol., 30 (2017) 115007.
[2] A. Gurevich and L.D. Cooley, Phys. Rev. B., 50 (1994) 13563.
[3] T. Okada $et$ $al.$, to be submitted.
[4] J. Luo $et$ $al.$, IEEE TAS under review.
Cuprate and iron-based superconductor cables offer powerful opportunities for increasing capacity, reliability, and efficiency of the electricity grid. Superconducting coils can provide an alternative to rare-earth permanent magnets used in rotary machines and generators. In this presentation, I will provide an overview of recent studies on the enhanced critical current density in cuprate and iron-based coated conductors using various ion irradiation. We demonstrated a roll-to-roll irradiation process on production-scale cuprate coated conductors that resulted in uniform enhancement of flux pinning at various dosage. At temperatures below 65K, we observed more than doubling of in-field critical current density Jc using roll-to-roll Au-ion irradiation process. Controlled annealing leads to a further enhancement of Jc at high temperatures and a recovery of the Tc reduction in the irradiated samples with high dosages. Superconducting properties and structural relations of the irradiated samples were characterized by using high resolution transmission electron microscopy (HRTEM) and atomically resolved electron energy loss spectroscopy (EELS) before and after the annealing. In iron-based superconductors, we have grown iron-chalcogenide superconducting films on various single crystal substrates and metal substrates with enhanced transition temperature Tc and high Jc. Simultaneous increase of Tc and Jc was observed in iron chalcogenide FeSe0.5Te0.5 films by low energy proton irradiation. Extensive HRTEM analysis provides direct atomic-scale imaging of cascade defects and maps of strain field. Tc is enhanced due to the nanoscale compressive strain induced by the irradiations and proximity effect, whereas Jc is doubled under zero field at 4.2 K through strong vortex pinning by the cascade defects and surrounding nanoscale strain. Enhanced critical current in FeSe0.5Te0.5 films at all magnetic field orientations is observed by scalable gold ion irradiation. This robust and scalable route opens up an avenue to improve the performance of coated conductors.
Ion irradiation is a well-established technique to create a variety of structural defects, such as points, clusters and tracks in superconducting materials without the problem of sample-to-sample variation. Recently, ion irradiation in a low energy range (< several MeV) has received a renewed interest as a practical method for improving critical current density Jc in magnetic fields, due to compact accelerator, less radioactivation and less expensive to operate1). Low-energy ion beam can produce displacements of target atoms, which lead to vacancy-interstitial type of defects, including Frenkel pairs and their clusters in superconducting materials. These structural defects could be effective flux pinning centers in superconducting films.
We have grown iron-chalcogenide FeSe0.5Te0.5 (FST) thin films on CeO2 buffer layers using pulsed laser deposition2,3). These films exhibit enhanced superconducting transition temperature Tc (Tczero ~18.0 K), which is about 30% higher than that found in the bulk materials and superior high in-field Jc performance over the low temperature superconductors. We demonstrated a route to simultaneously raise Tc and Jc in FST thin films by using 190 keV proton irradiation1,4). Tc is enhanced due to the nanoscale compressive strain induced by cascade defects created by the low-energy proton irradiation. Jc is nearly doubled at 4.2 K up to 35 T perpendicular to the film surfaces through strong flux-pinning by the cascade defects and surrounding nanoscale strain. In this talk, we will present systematically the effect of 190 keV proton irradiation on superconducting properties and flux pinning in FST films. Also, we will discuss the relationship between critical current properties and defect structures produced by different irradiation energies and different ion species.
1) T. Ozaki et al., Supercond. Sci. Technol. 33, 094008 (2020).
2) Q. Li, et al., Rep. Prog. Phys. 74 124510 (2011).
3) W. Si, et al., Nat. Commun. 4, 1347 (2013).
4) T. Ozaki et al., Nat. Commun. 7, 13036 (2016).
The electronic transport and optical properties of high quality multilayers of NbTiN/AlN with ultrathin NbTiN layers were characterized. The anisotropy of the dielectric function of the multilayers confirmed their hyperbolic metamaterial properties. The superconductive transition temperature, Tc, of these engineered superconductors was enhanced up to 32% compared to the Tc of a single ultrathin NbTiN layer while the resistivity per NbTiN layer remained unchanged. We have demonstrated that this Tc increase can be attributed to enhanced electron–electron interaction in superconducting hyperbolic metamaterials. The measured critical fields are high and have an anomalous temperature dependence on the direction perpendicular to the magnetic field. These results demonstrate that the metamaterial engineering approach can be used to enhance Hc2.
This work was supported in part by DARPA under Award No. W911NF-17-1-0348 “Metamaterial Superconductors”; by ONR under Award Nos. N0001418-1-2681, N0001418WX00078, and N00014-18- 1-2653; and by ONR under the Naval Research Laboratory base program. A.-M. Valente-Feliciano and D.R. Beverstock are also supported by the U.S. Department of Energy, Office of Science, and Office of Nuclear Physics under Contract No. DE-AC05-06OR23177.
Hydrogen has tremendous potential to become a next-generation, environmentally friendly energy carrier that will help mitigate climate change, reduce the world’s dependence on fossil energy, and complement renewable energy sources on or off the grid (i.e. wind, solar, and hydro). One commercial application for this technology is fuel cell electric vehicles (FCEVs), a technology that automotive companies have invested significantly. For the past decade, the FCEV industry focused primarily on the development of light-duty (LD) vehicles, and these cars were released to the market along with the first hydrogen fueling stations to support them. Recently, FCEV technology is moving into the medium-duty (MD) and heavy-duty (HD) markets. These vehicles require more fuel to operate due to size, extreme duty cycles, and range requirements, and they subsequently require larger associated fueling infrastructure. Most modern hydrogen stations and vehicles store hydrogen as compressed gas, however, in order to address increasing storage requirements for station and vehicles, it would be beneficial to store hydrogen at higher densities. One method that has been identified for storing hydrogen at higher density is to store it in liquid form. The density of liquid hydrogen is about 76% higher than that of gaseous hydrogen, enabling significant space savings.
The National Renewable Energy Laboratory (NREL) is in the process of adding the capabilities to perform experiments and numerical simulations of liquid hydrogen storage and fueling. Currently, liquid hydrogen is used for ground storage due to its high density, and it is converted to gaseous hydrogen when needed to fuel FCEVs. Therefore, to understand hydrogen fueling involving liquid storage, we need to model the two-phase flow including the thermodynamic behavior of both gaseous and liquid hydrogen phases and their interactions. NREL has previously completed a study focusing on the thermodynamic behavior of gaseous hydrogen during a fueling event from a station to a vehicle. The model has been validated with experimental data and has laid the groundwork for developing models of other hydrogen fueling types.
In future work, this study aims to model liquid hydrogen used by fueling stations with physics-based equations. To build a reliable model, various data would be required, including the geometry and materials of the storage system, how temperature and pressure are managed between fills, and other operational conditions of a fill including, e.g., what the flow rates are. The liquid hydrogen model could be integrated with the gaseous model, and insights from the integrated two-phase flow model would help station providers build an efficient and effective liquid storage system. In the future, it is expected that FCEV technology will expand into other applications such as rail, marine, and aviation. At that time, liquid hydrogen may be critical to the success of infrastructure and the associated transportation systems due to size of the vehicles, range requirements, and fueling requirements.
The US Navy has been investing in superconducting technology for the past 80 years. The most recent developments have been in the area of low- and medium-voltage direct current (DC) cables and large-bore magnets, and superconducting magnetic energy storage (SMES). Low-voltage DC cables are most useful in the control of a ship’s magnetic signature as part of a degaussing system. Significant progress towards implementing this aboard US Navy vessels has been made and is currently being installed. Medium-voltage power system components have been under development the past several years through programs aimed at di-electrics, warm-to-cold transitions, connectors, etc.; as well as, cryogenic refrigeration. Large-bore magnets have been a focus over the past decade and are planned to transition in the next five years. Additionally, the Navy has launched an investigative study on the relevance of SMES for use in applications aboard naval vessels. The invited talk for will include current status of the Navy’s recent transition of low-voltage DC cables to the Fleet, topics on medium-voltage power system components, the next stage of development and potential transition of large-bore superconducting magnets, and initial results and potential use of SMES in naval applications.
Hold time of an adiabatic demagnetization refrigerator(ADR) is very important for astronomy missions. The hold time depends on two factors, ADR’s cooling power and heat load. Generally, the cooling power of an ADR is small. It becomes necessary to minimize heat load. A main source of heat load comes from the gas gap heat switch (GGHS). When the GGHS is in OFF status, the heat load is demined by the hermetic outer tube, which is usually made by metal alloys. Ceramicnd polymer materials have a low thermal conductivity at low temperature. This feature makes them possible to play the role of hermetic outer tube. In order to verify the feasibility, the thermal conductivity of several candidates were tested down to 200mK.A GGHS prototype was made and the helium leakage test were done after 10 times temperature cycle. The test result is shown and discussed in this paper.
High sensitivity astrophysics detectors such as transition edge sensor (TES) bolometers or microwave kinetic inductance detectors (MKIDs) require sub-Kelvin operating temperatures for observing low energy photons in infrared and x-ray ranges. Continuous Adiabatic Demagnetization Refrigerators (CADRs) are presently the state of the art solution for providing cooling to these detectors below as low as 50 mK. The CADR shuttles heat through a series of paramagnetic stages from a 50 mK heat load to a 1-6+ K heat sink, using heat switches between stages to “switch" between thermal isolation and thermal communication. A superconducting heat switch is required between the two lowest temperature stages and is considered a critical system component as it determines recycling time and cooling power of the lowest temperature stage. A figure of merit for this technology is the “switching ratio”: the ratio of the thermal conductivity in the on and off states. This ratio is a function of temperature, fixed material properties, and the purity and anneal state of the metal. Lead is most commonly used in this type of thermal switch because it is readily available as a high purity material. However, an analysis of the material properties of other superconducting material suggests that vanadium could achieve a significantly higher switching ratio - as high as 20x that of lead. Increasing the switching ratio could allow for shorter recycling times and reduce the parasitic load on the lowest temperature stage. This work discusses the design of a vanadium superconducting heat switch and compares predicted performance in the CADR against the presently used lead switch.
The astrophysics Xray Imaging and Spectroscopy Mission (XRISM) contains two instruments. The spectrometer, Resolve, uses x-ray microcalorimeters operating at 50 mK to obtain photon-limited spectroscopy in the 0.5 to 10 keV range. As a precooler to the Adiabatic Demagnetization Refrigerator that reaches 50 mK, a 40 liter superfluid helium dewar and a 4.5 K Joule-Thomson cooler are used. Early in the ground test program the helium dewar developed a low temperature leak. Despite having a getter within the dewar, the leak would have prevented a successful mission. This paper describes the leak that was found, its repair, and the leak measurements that were performed on the 10 cool downs after repair before launch. We will also list lessons learned from the experience.
Liquid Nitrogen precooling is used in most Cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF Superfluid Cryoplant, where the Helium supply directly exchanges heat with liquid Nitrogen, freezing of Nitrogen occurred inside the heat exchanger due to heat exchanger imbalance during a Cryoplant trip. Trapped vapor pockets of N2 within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming Helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold Helium gas from cold end during abrupt Cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of Nitrogen which can damage to the heat exchanger.
Recuperative heat exchangers play an important role and have a large influence on the overall efficiency in many cryogenic systems. The recuperators to achieve fast cooldown can be summarized as effective, compact, and low pressure-drop. Designing this type of heat exchanger has been a challenge, especially when the size and effectiveness objectives are becoming more and more strict with the development of the application scenarios. In this study, a meso-scale helical-tube-bundle heat exchanger is proposed, with the configuration as twisting several tubes into one bundle, then twisting several bundles into the whole geometry. All the tube paths are generated by 3D sinusoidal equations, leading to same developing length and average coil diameter, promoting uniform distribution and fluid mixing. The thermal and hydraulic performances of shell side flow and tube side flow are simulated respectively by Fluent. The Nu and friction factor correlations for both sides are developed and used in the whole heat exchanger model. A 1D finite difference model considering axial conduction, thermal properties variation and parasitic heat load is built to estimate the effectiveness and pressure drop of the whole heat exchanger. A geometry with 432 tubes in parallel is found to meet all design objectives: operation between 300 K and 30 K, mass flow up to 12 g/s, size 0.3 m×0.3 m×0.7 m, effectiveness > 0.99, pressure drop for both sides <1 bar.
Practical regenerative refrigerators are capable of working down to 4 K and largely fulfill the refrigeration requirement of modern technologies in many fields, especially for space applications. However, the enthalpy flow associated with the pressure dependence, abbreviated as pressure-induced enthalpy flow, brought about by real gas effects degrades the theoretical COP of the refrigerator to below about 30% of the Carnot efficiency at the temperatures of below the critical point. This paper summarizes important explorations of uncovering the loss mechanism and reducing such losses in the regenerator. It is emphasized in this paper that the main factor leading to the real gas losses in the regenerator is the heat-associated enthalpy flow, which is used to balance the variation of the pressure-induced enthalpy flow, resulting in an entropy generation. The physical mechanism of reducing real gas losses, including the heat input or removal method and the DC flow method will be discussed. We further carry out analyses on the expansion component of the pulse tube. The real gas effects on the pulse tube is mainly the enlargement of the heat-associated enthalpy flow in the case when the pressure-induced enthalpy flow is negative, thus the heat transfer between the gas and the wall gets enhanced. Several inferences are made in order to explore the long-lasting puzzles about real gas effects, including the synthetic effect of the DC flow through the whole refrigerator. It is emphasized that the underlying cause of the loss in the regenerator is an indirect effect of the real gas properties. Further study about carrying out a direct verification of the theory is proposed.
The ITER Cryogenic Lines (CLs) system is a complex network intended to distribute helium at three main nominal temperature levels (4 K, 50 K and 80 K) in order to fulfil the requirements of Cryogenic system end users called clients (mainly magnet feeders (CTBs) and cryopump Cold Valves Boxes (CVBs)). The installation of Cryolines in particular in the Tokamak building is a very challenging and highly integrated task due to complex shapes of CLs segments, coactivity and the congestion of the area with the presence of many equipment in their vicinity.
The aim of this paper is to provide the ongoing status of installation works of complex cryolines, as well as the upcoming phases will be presented. After detailed description of the ITER CLs system and its design particularities, the assembly and installation plan developed will be presented. A focus will be made on developed different operating modes and associated tools considering the layout constraints and complexity arising from the integrated installation in the Tokamak building.
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
As part of the ITER vacuum system’s front end cryo distribution system, 12 complex cryogenic valve boxes (CVBs) and a warm regeneration box (WRB) are required to supply the torus, cryostat (T&C) and neutral beam (NB) cryogenic pumps. This cryogenic distribution system has to operate in a demanding environment within ITER’s main Tokamak building where they will experience high magnetic fields, ionizing radiation and need to cope with abnormal events such as seismic activity. In addition, this distribution system has to fit in a very limited space, be maintainable, highly reliable and integrate with many other systems. Uniquely, the CVBs cryogenic circuits operate over a wide temperature range between 4 K and 500 K during cryopump operation and regeneration. The process and operating environment has given particular challenges for material and instrument selection and implies that many standard cryogenic components, such as cryogenic valves, temperature sensors and pressure relief devices, have had to be adapted.
Each of the CVBs presented consists of a vacuum vessel with a diameter of about 1.8 m and a height of 1.9 m, an internal thermal radiation shield, 23 to 30 cryogenic valves, 10 to 20 pressure relief valves, 4 bursting discs, a flow meter, more than 80 temperature sensors and various optical pressure transducers and is mounted on a support frame equipped with maintenance platforms. The design includes smart features such as a manhole and optimized piping to allow access to internal components. Currently, the final design of the WRB and CVBs and the manufacturing of the WRB and eight T&C CVBs have been completed. The manufacturing phase of the NB CVBs has just started. The work described is performed on behalf of Fusion for Energy (F4E, OPE-843, OPE-1249), the European organisation managing Europe’s contribution to ITER.
This paper summarises the challenges of the design, manufacturing and assembly of the WRB and CVBs taking into account the unique environment and stringent ITER requirements. In particular, it provides an overview of the final designs, the materials used, modifications and further developments of standard cryogenic components and instrumentation.
The ITER cryogenic system will be the largest concentrated cryogenic system in the world serving multiple client system (superconducting magnets, plasma fueling and vacuum pumping). Cryogenic technology will be extensively used at ITER to create and maintain low-temperature conditions for vacuum pumping. US ITER is responsible for the design, fabrication, and delivery of the roughing pump system (RPS) Cryogenic System which among other things, regenerates the torus and neutral beam cryogenic pumps of the ITER tokamak. In the process exhaust gas stream, common gases (nitrogen, air, helium, etc.) can be found, as well as hydrogen isotopes (H2, D2, T2, and combinations of). The RPS Cryogenic System separates the hydrogen isotopes, allowing processing of the exhaust gas stream. The RPS Cryogenic System consists of Cryogenic Viscous-flow Compressors (CVC), Condensable Vapor Devices (CVD), Cryogenic Distribution Boxes (CDB), and the Cryogenic Transfer Lines (CTL). The Cryogenic Forevacuum Exhaust System is backed by roots pumps while the Cryogenic Forevacuum Roughing Train consists of scroll pumps. Gaseous helium (GHe) and super critical helium (SCHe) are supplied via the CTLs to the CDB. The GHe is distributed to the CVD and CVC, while the SCHe is processed through a liquid helium (LHe) bath to achieve a temperature range of 3.5K to 4.2K. The GHe supplied to the CVD is used to freeze water within the process gas stream, protecting the CVC from accumulating water. GHe is supplied to the CVCs to create a thermal shield and to precool the incoming exhaust stream. The SCHe is sent to the CVC condenser, and the hydrogen isotopes are separated from the process gas stream using helical tubes that direct the flow radially towards the cold tube walls and back to the center. This avoids radial gradients in the flow and is required for the complete phase change of the hydrogen isotopes. The process gas stream exiting the CVC is sent for processing, while the CVC continues to collect hydrogen isotopes. During regeneration of the CVC, the CDB will send a mixture of 80K GHe and ScHE to the condenser to warm up the hydrogen isotopes to allow a controlled release, which will then be processed. In total, the RPS Cryogenic System will allow ITER to engage in the critical science of developing sustainable burning plasma operations to facilitate the design and construction of commercial fusion power plants.
The paper will present a complete methodology for designing a support system for process pipes in cryogenic multi-channel vacuum insulated transfer lines on the example of a BayonetCan module dedicated to the PIP II accelerator infrastructure at FermiLab. The process of constructing fixed and sliding supports, in particular supports dedicated to cooperation with compensation bellows, will be discussed. The paper defines the scope of requirements for supports in accordance with EN 13480, ISO EN 21009 and EN 14917 standards. It also presents a comparison of these requirements with those of equivalent American standards such as ASME B31.3 and ASME BPVC. Load definition, selection of materials and optimization of the structure in mechanical and thermal terms. The discussed supports were analyzed using the finite element method, the paper will present the results of thermal analysis in the form of temperature profiles and heat inputs as well as mechanical properties such as stiffness, buckling strength and stress values.
Polish Free Electron Laser facility (PolFEL), presently under construction at National Center for Nuclear Research in Warsaw will consist of electron gun and four cryomodules each housing two 9-cell superconducting TESLA RF cavities. The cryomodules comprising the cavities will be supplied with superfluid helium at 2 K. Other PolFEL cooling power requirements result from the demand of the power couplers for the accelerating cryomodules (5K) and thermal shields (40 K – 80 K). The machine will make use of several helium thermodynamic states like two-phase superfluid HeII, supercritical helium and low pressure helium vapors supplied to cold compressors. Cryogenic Distribution System (CDS) will provide supercritical helium to the valve-boxes where thermodynamic processing of the helium to superfluid state will take place. The paper presents the CDS architecture and discusses the possible design options like methods of the power couplers cooling, optional use and location of cold compressors. The second law of thermodynamics has been used for the optimization of the CDS configuration. Generalized approach to the design of helium distribution systems, taking into account thermomechanical aspects and the consequences of the second law of thermodynamics, is presented.
A main distribution box is a large cryogenic valve box which connects two cryoplants with two superconducting linear accelerators (LINACs) of Korean heavy ion accelerator. A major role of the main distribution box is transferring cryogenic helium from the cryoplants to LINACs and controlling flow rate of the helium. It can take other several roles when it encounters special situations. It has total 44 cryogenic valves to manage the helium. DN10 to DN250 valves are applied according to sizes of the cryogenic lines in the main distribution box. Designed heat loads of the main distribution box are 440 W for thermal shield, 24 W for 4.5 K lines and 43 W for 2 K line. At present, the main distribution box keeps its cold status and is operated well although it needs some improvements. The improvements will be gradually carried out when our cryogenic system will be warmed up. Some occurred issues, our solutions and current status of the main distribution box are shared in this paper.
A new accelerator facility called FAIR is being built at GSI in Germany. The accelerator will accelerate all particles of all the chemical elements. SIS100, the main accelerator ring, requires a cryogenic distribution system that consists of tailor-made (project-specific) multiple helium vacuum-insulated transfer lines and valve boxes. An inside of the required cryogenic equipment and associated complexity will be given. The main technical challenges of the project such as heat load, pressure drop, and space will be presented including proposed technical solutions.
The Sanford Underground Research Facility (SURF) will host the Far Detectors of the Deep Underground Neutrino Experiment (DUNE), an international multi-kiloton Long-Baseline neutrino experiment that will be installed about a mile underground in Lead, SD. Detectors will be located inside four cryostats filled with almost 70,000 metric tons of ultrapure liquid argon, with a level of impurities lower than 100 parts per trillion of oxygen equivalent contamination. The cryogenics infrastructure supporting this experiment is provided by the Long-Baseline Neutrino Facility (LBNF). This contribution presents modes of operation, layout and main features of the LBNF Far Detectors cryogenics system, which is composed of the following subsystems: argon receiving facilities, nitrogen system, argon distribution system, argon purification and regeneration systems, argon circulation system, argon condensers system, internal cryogenics, miscellaneous items, and process controls.
The argon receiving facilities include the equipment to receive the argon in liquid phase on the surface, vaporize it and transfer it underground as a gas.
The nitrogen system provides cryogenic refrigeration and is composed of a refrigeration system, liquid nitrogen buffer tanks and liquid and gaseous nitrogen distribution pipes to and from the argon condensers and other users.
The argon distribution system distributes liquid and gaseous argon to and from the purification system and the condensers and the cryostats.
The argon purification and regeneration system purifies gaseous and liquid argon to the level required by the experiment using molecular sieve and copper beds. The media requires activation prior to its use and periodic regeneration cycles throughout the life of the experiment to release the impurities that are being removed from the argon and trapped inside the media.
The argon circulation system consists of two sets of pumps to circulate the bulk of the liquid and the recondensed argon through the purification system and back to the cryostat.
The argon condensers system consists of condensers and nitrogen and argon phase separators to recondense the boil-off argon from the cryostat and deliver the purified argon back to the cryostat.
The internal cryogenics comprises the liquid and gaseous argon distribution inside each cryostat for the commissioning, cool down, fill and steady state operations of the cryostats and detectors.
The miscellaneous items consist mainly of the cryostat boil-off, pressure control systems and some other ancillary equipment.
The process controls provide the means to monitor and operate the systems. They include Programmable Logic Controller (PLC) cabinets, wiring, Human-Machine Interface (HMI), programming, and Oxygen Deficiency Hazard (ODH) hardware and software.
An international engineering team is designing these systems and will manufacture, install, test, commission, and qualify them. This contribution describes the main features, performance, functional requirements and modes of operation of the LBNF Far Detectors cryogenics system. It also presents the status of the design, along with present and future needs to support the DUNE experiment.
United Launch Alliance (ULA) is proud to partner with NASA for the launch of a Cryogenic Fluid Management (CFM) Tipping Point Flight Demonstration. This presentation will provide an overview of the flight experiment that ULA will be designing, building, testing, and launching in support of NASA and space technology advancement objectives. The CFM technologies that ULA will launch for the first time as part of this rideshare flight demonstration, will directly lead to significant advancements in the fields of space launch and space exploration.
The sustainable exploration of space will rely on refueling and reuse of spacecraft and rocket stages. This will require propellant depots where cryogenic fluids are stored and then transferred into customer tanks. The long-term storage and transfer of cryogenic propellants in space has never been demonstrated. NASA has funded several projects to demonstrate these technologies in orbit and among the projects is the LOXSAT payload being built by Eta Space. The LOXSAT demonstration mission will advance the Technology Readiness Level of up to 13 individual LOX storage and transfer technologies during a 9-month mission. Upon successful demonstration, Eta Space will develop Cryo-Dock, a full-scale propellant depot in low Earth orbit standardized for commercial operations. This paper will present the goals and objectives of the LOXSAT mission, current project status, and plans for future systems development.
NASA Science and Technology Mission Directorate is investing in advancement of on-orbit cryogenic fluid management technologies by partnering with industry through multiple “Tipping Point” contracts with the primary objective of reducing development costs and schedules for infusion into long duration missions utilizing cryogenic propellant. Lockheed Martin was selected as a partner in 2020 to conduct a demonstration of CFM technologies through an integrated payload system designated the Cryogenic Demonstration Mission (CDM). This presentation provides a summary of the CDM top-level goals, contract objectives, and progress completed to date.
NASA Science and Technology Mission Directorate is investing in advancement of on-orbit cryogenic fluid management technologies by partnering with industry through Tipping Point contracts with the primary objective of reducing development costs and schedules for infusion into long duration missions utilizing cryogenic propellant. SpaceX was selected as a partner in 2020 to conduct a demonstration of CFM technologies on a Starship Mission. This presentation provides a summary of the top-level goals and objectives of this contract and how NASA has structured this partnership.
It is important to minimize the density of all materials in electric aircraft, which includes materials selected for structural and electrical conductor components. Thus, aluminum (Al) alloys are chosen for the airplane skin and many of the internal support members. Pure Al has two key advantages for use as the prime electrical conductor: low density and good electrical conductivity. At very low temperatures and in a magnetic field, the conductivity advantage increases, and at 20K, this advantage can be substantially better than pure copper (Cu). The results reported include strength and resistivity of high RRR Al and dilute Al alloy from room temperature to 4.2 K. Information regarding the degradation of resistivity with cryogenic cyclic strain is included. The results presented should help with the evaluation of pure Al for use at cryogenic temperatures in electric airplanes.
Ultrahigh conductivity Al (Al hyperconductors, RRR ~10^4) has the capacity to be competitive with superconductors at cryogenic temperatures. High-purity Al (HPAL) conductivity has the benefits of not being dependent on a transition temperature, Tc, allowing for a wider range of operational temperatures, and has lower ohmic heating contributions than superconductors in high-frequency bands. However, its low yield strength makes for a difficult manufacturing process and is unfeasible for applications with high applied field. To remedy this issue, a metal matrix composite (Cu-30Ni) is used around the aluminum core to increase the conductor strength, while ensuring high performance in the aluminum by limiting the interdiffusion between the materials. We report the resistivity ratio (RR) as a measure of how well the HPAL is preserved for various metal matrix composites around the aluminum core in an applied magnetic field for temperatures from room temperature down to 4 K. We also explore the aluminum cold work degradations during wire drawing and proper heat-treatment methods to recover the high RRR without introducing undesired imperfections from the metal matrix. We then compare the RR values for multifilamentary conductors designed for AC loss applications with non-altered conductors to see any variations in performance.
Ferrite and austenite duplex stainless steels exhibit an excellent strength-ductility balance at low temperatures. On the other hand, it is well known that grain refinement improves not only the strength but also the toughness of metal materials. In this study, the effects of grain size on the low-temperature tensile properties in ferrite and austenite duplex stainless steel having different grain sizes were revealed, and then, the improvement mechanisms of the properties by grain refinement were discussed based on the obtained deformation behavior. Three specimens of duplex stainless steel with identical chemical compositions in each phase and phase ratio but different grain sizes ranging from 2.0 to 7.4 μm were prepared. At room temperature, the strength increased, but the elongation decreased with refining the grain size. Whereas, at 77 K, both strength and elongation were increased by grain refinement. The formation of deformation-induced martensites was detected in the fractured specimens at 77 K, and its volume fraction increased with refining the grain size. Therefore, the transformation-induced plasticity effect should provide high elongation at 77 K in the fine-grained specimen. The increase in strength by grain refinement strengthening at 77 K was significantly larger than that at room temperature. These results strongly suggest that grain refinement effectively improves the low-temperature tensile properties in the ferrite and austenite duplex stainless steel.
Acknowledgement
This study is supported by JFE 21st Century Foundation.
The austenitic stainless steels, such as type 304L (18Cr-9Ni, mass%) and 316L (16Cr-10Ni-2Mo), are widely used in cryogenic applications. However, their strength is relatively low, and the martensitic transformation appears when they are strained at low temperature. For structural applications at 4.2 K, therefore, type 316LN (17Cr-11Ni-2Mo-0.2N) nitrogen-strengthened austenitic stainless steel is commonly used for its high strength and toughness, thermodynamic stability, and excellent weldability. To advance the understanding of metallic materials for structural components at cryogenic temperatures, the 0.2% proof stress and fracture toughness of type 304 and 316 austenitic steels at 4.2 K in the literatures are summarized with the NIST trend for 300 series. The data which are for rolled plates, not very thick plates exhibit a trade-off relationship. These references may serve as a useful decision-making tool during initial mechanical design as well as for further alloy development.
The plane strain fracture toughness of type 316LN steel depends on its stability at 4.2 K, which is characterized by the Md30 index. Here, the Md30 is the temperature (K) at which 50% volume of austenite matrix transforms to martensite under a true strain of 0.30 in tension for single-phase austenitic steels. The Md30 of the plates correlated well with their respective fracture toughness values, where a higher Md30 indicated lower fracture toughness. Low plastic strains were responsible for an increase of α’-martensite formation at the crack tip. An alloy design having a higher Ni, Mn and Mo, and lower N content in its chemical composition would be favorable for type 316LN steel to provide a higher fracture toughness owing to higher stacking fault energy.
In this paper, real-time strain monitoring of epoxy resin and glass fiber reinforced composites was explored using embedded FBG from curing process to high temperature (413 K), cooling down to cryogenic temperature (4.2 K), and three-point bending experiment. The experimental data tested by FBG was compared with results got by strain gauges and extensometers. It was found that trend of strain response of sample obtained by FBG and strain gauge from curing process to high temperature and cryogenic temperature is the same. The maximum deviation between the strain value monitored by FBG in real time and the standard data is 5%, and the maximum deviation between the strain value monitored in real time by the strain gauge and the standard data is 15%. The measured value of the strain gauge is smaller than the standard data, indicating that the FBG has higher sensitivity and accuracy to the measurement of strain. FBG was successfully used to monitor room temperature flexural fracture failure of composites, and the elastic deformation of the material before flexural fracture. FBG can be used to monitor the flexural fracture failure of composite materials at liquid nitrogen temperature (77 K), and micro strain value (<100 ) of the material before flexural fracture.
High Temperature Superconducting (HTS) power systems are being developed for a variety of applications including the electrical power grid, industrial applications, data centers, high energy physics, electric ships, and electric aircraft. There are some common requirements and design features for HTS devices for all the applications. However, the design requirements for electric transportation applications such as electric aircraft and electric ships need high gravimetric and volumetric power densities. The power density demands require that the HTS generators and motors in electric transportation applications operate at a temperature between 20 and 50 K to compensate for the reduction in critical current density and AC losses under the substantial magnetic fields present in the rotating machines. HTS power distribution cables support high enough current densities when operated at higher temperatures of 40 - 60 K. The challenges with power cables that carry multiple kA are the cable terminations, current leads, and cryogenic interfaces. Innovative designs are needed to address the challenges of low dielectrics and cryogenic thermal designs. Versatile lightweight heat exchangers and secondary cooling loops for effective utilization of the cryogenic cooling power of liquid hydrogen fuel from 20 K to 300 K need to be developed. Cryogenic thermal storage systems are needed for resiliency against unexpected heat loads and to maintain the temperature of some cryogenic components during ground stops. We at the Center for Advanced Power Systems (CAPS) are collaborating with other academic institutions and several small businesses to address the challenges of AC losses in HTS rotating machines and making the interfaces (terminations) for HTS cable systems compact. We have ongoing work on cryogenic dielectric and cooling systems for HTS applications for electric transportation applications. The Presentation will focus on the ongoing research and recent collaborative accomplishments in these areas. Collaborative efforts include superconducting technologies and cryogenics for zero emission electric aircraft.
Acknowledgement: Our research is funded by the Office of Naval Research, Department of Energy, and the National Aeronautics and Space Administration.
The Center for Cryogenic High-Efficiency Electrical Technologies for Aircraft (CHEETA) project and Hyper Tech Research Inc. are developing demonstrations of a cryogenically cooled, low to medium voltage, high amperage, and lightweight aerospace power cable. The research presented here includes the motivation behind these demonstrations, challenges for these demonstrations, demonstration designs, and results of some derisking tasks.
Cryogenic power electronics is both advantageous and indispensable in many applications, like deep space probe, military electric vehicle, magnetic resonance imaging etc. Among different semiconductors, the gallium nitride (GaN) high electron mobility transistor (HEMT) is the most promising candidate for cryogenic applications with significant conduction loss and switching loss reductions. In this work, the GaN HEMT power converters with different power levels (from several Watts to several kiloWatts) are evaluated at cryogenic temperature. Three different commercial GaN HEMTs are used in these power converters, including the Texas Instruments LMG5200 80 V GaN half-bridge power stage with integrated gate driver, the GaN Systems 650 V bottom cooled GaN HEMT GS66516B, and the 650 V top cooled GaN HEMT GS66516T from GaN Systems. Moreover, different converter evaluation methods are investigated. Three of these power converters are evaluated by using a cryogenic chamber and such that the converter operating environment temperature can be regulated. One of the power converters is evaluated by using liquid nitrogen (LN2) channeled through a cold plate, where the gate driver can be designed to operate at non-cryogenic temperatures. Due to the degraded performance of conventional magnetic components, air core magnetics are used in these power converters to improve the converter efficiency.
All the evaluated GaN HEMT based power converters have demonstrated improved efficiency performance at cryogenic temperatures. The individual converter efficiency performances are summarized as follows: 1) 2.5 MHz 4 W LMG5200 based inductive power transfer (IPT) converter: the converter efficiency at room temperature is 58.56%, while this value is increased up to 78.2% at 93 K; 2) 500 kHz 80 W LMG5200 based Buck converter: the converter efficiency increases from 90.67% at room temperature to 97.53% at 93 K; Further, the integrated gate driver for the LMG5200 works properly at LN2 temperature; 3) 300 kHz 700 W GS66516B based Boost converter: the converter efficiency at rated output power and room temperature is 95.97%, while the converter efficiency increases up to 96.56% at 148 K. The converter is not evaluated at even lower temperatures due to the malfunction of the gate driver; 4) 150 kHz 5 kW GS66516T based Buck converter: a cryogenic power electronics structure is adopted to avoid the malfunction of gate driver and the cold plate is used to achieve cryogenic temperature. Maximum efficiency of 98.5% is achieved at 1.5 kW output power and around 1% efficiency improvement can be achieved when compared with room temperature operation at 130 K.
Loss distribution analysis for the power converters is cataloged. There are two major reasons for efficiency improvement at cryogenic temperatures for these power converters: 1) switching loss and conduction loss reductions for GaN HEMTs; 2) conduction loss reductions for air core magnetics since the copper resistance is reduced at cryogenic temperature. Overall, GaN HEMT and air core magnetics-based power converters are very promising for cryogenic applications. The final paper will discuss the details of power converters performances and loss distribution analysis.
Highly efficient electrically driven avionics have led to a renewed interest in cryogenic propulsion systems with the goal of reducing carbon emission footprint. Although cryogenic converters promise better efficiency and improved power density, a successful design is incumbent upon the appropriate switching device selection and simulation-based analyses performed prior to initial prototyping. In this work, a datasheet-driven compact model for a gallium nitride (GaN) Gate Injection Transistor (GIT) has been proposed and implemented in LTspice, a versatile, high-performance, and free circuit simulator. GaN-GIT is a very promising High Electron Mobility Transistor (HEMT) structure that allows a normally off (E-mode) fail-safe operation and is deemed to be an excellent candidate for cryogenic applications like aircraft due to the absence of “carrier freeze-out” effects. The structure demonstrates “conductivity modulation” at gate voltages higher than the gate built-in voltage without compromising the normal field-effect transistor (FET) like operation in ON and OFF states. Further, the structure allows for lower gate leakage due to the AlGaN/GaN barrier prohibiting the back flow of electrons to the p-GaN layer.
Apart from accurately modeling the channel current in both the first and third quadrants, the model includes the dc gate leakage current inherent to GaN technology. In addition, none of the available GaN-GIT models considers the “conductivity modulation” due to hole injection. In this work, a secondary path for channel current has been defined as the gate voltage surpasses the built-in potential. In order to capture the dynamic behavior accurately, a phenomenological modeling approach has been undertaken to model the interelectrode capacitances. The vendors’ provided model uses conventional JFET-based capacitance modeling, which fails to incorporate the transition in capacitance at corresponding field-plate pinch-off voltages. Model parameter extraction is completely datasheet-driven, so the designer requires no restricted device processing parameters. In addition, LTspice being a free simulator, designers can easily automate the extraction procedure in a co-simulation approach using Python, MATLAB, etc. Finally, the temperature scaling in available models is limited to room temperature and higher, which, if extrapolated for lower temperatures, will inadvertently result in incorrect predictions. All three important parameters of a GaN-GIT e.g., threshold voltage, transconductance, and on-state resistance, present strong sensitivity to temperature. The on-resistance reduces due to an increase in electron mobility. The increase in the threshold voltage can be attributed to the hole injection from the metal gate to the p-GaN layer and their accumulation near the interface. The transconductance increases with the channel mobility and carrier velocity increase.
A commercial GaN GIT (31A/600V) has been characterized for this work with a parametric curve tracer. For cryogenic measurements, a thermal chamber connected to a liquid nitrogen dewar was deployed.
This paper aims to implement a datasheet-driven GaN-GIT HEMT model in LTspice with accurate static and dynamic behavior to provide a means for designers to select the best devices for an appropriate wide temperature range. Additional complex converter topologies, such as a Cascaded H-Bridge (CHB) multilevel inverter, will be simulated to demonstrate the model’s convergence robustness. This work has been supported by the NASA ULI: Development of the CHEETA Design Concept.
A sub-transmission technology using 2G HTS wires with high engineering current density is developed in the SuperLink project. The goal of the project is to supply a versatile and easy-to-install 110 kV power-link adapted to the conditions in city areas such as Munich, Germany. The realization of power links of 500 MW over 10-20 km lengths requires high performance in the AC loss of the HTS conductors, strong and compact cryogenic dielectrics and energy-efficient thermal insulation. This work presents the basic designs concepts of the SuperLink Cable as well as a deep investigation of its effects in the 110 kV network. Load flow calculations were performed considering the network operation under different load and feeding scenarios. In order to evaluate the results, the loading of the lines, as well as voltage stability and short circuit current levels were analyzed. It was found that the SuperLink cable contributes not only to the relief of overloaded cables but also to the overall decrease of the losses in the network.
Using 4-µm-thick REBCO film and optimal film composition, we had demonstrated critical currents as high as 1,836 A/4mm at 4.2 K, 20 T (Jc = 11.5 MA/cm2). Recently, we scaled up this process to 50-m-lengths to achieve 1,274 A/4 mm at 4.2 K, 20 T (Jc = 8 MA/cm2) which about 70% of the short-sample champion value. Achieving uniform, repeatable and high in-field critical current over long tape lengths requires excellent control of pinning landscape in these high-performance tapes made by our advanced metal organic chemical vapor deposition (MOCVD) process. The A-MOCVD technique provides an opportunity to double the high critical currents by simultaneous double-sided deposition. Our progress in these areas will be described in this presentation.
This work was supported by awards DE-EE0007869 from the US Department of Energy (DOE) Advanced Manufacturing Office, DE-AR0001374 from Advanced Research Projects Agency-Energy (ARPA-E), DE-SC0016220 from the DOE Office of High Energy Physics, and N68335-21-C-0525 from Naval Air Systems Command (NAVSEA) through AMPeers LLC.
In addition to naturally induced pinning centers in $RE$Ba$_{2}$Cu$_{3}$O$_{7−\delta}$ coated conductors ($RE$BCO-CCs), such as blocking layers and stacking faults act as planer pins, minor-phase precipitates and oxygen defects act as coarse and fine spherical pins, an introduction of fine pinning centers plays a crucial role for improving the critical current density Jc characteristics of $RE$BCO-CCs. Regarding fine spherical pins, $RE$$_{2}$O$_{3}$ nano-particles with a PLD technique [1] and Ba(Hf/Zr)O$_{3}$ (BHO/BZO) nano-particles with TFA-MOD [2] and F-free MOD [3] methods have been introduced, and an anomalous depression of $J_{\rm c}(\theta\sim B\parallel ab)$ at low fields and a crossover to an usual effective mass like $J_{\rm c}(\theta)$ at high fields, have been observed in some cases [2, 4]. As for columnar defects, Fujikura successfully introduced short BHO nano-rods via their Hot-wall PLD with a fast growth rate and reported $J_{\rm c}(T, B, \theta)$ with a smaller anisotropy, namely with a less remarkable $J_{\rm c}(B\parallel c)$ peak, compared with $J_{\rm c}(T, B, \theta)$ caused by well-aligned nano-rods [5].
For further improving the $J_{\rm c}(T, B, \theta)$ characteristics of $RE$BCO-CCs, it is important and beneficial to understand such novel $J_{\rm c}(T, B, \theta)$ characteristics due to artificial pinning centers. In this study, we calculated the angular dependence of the elementary pinning force $f_{\rm p}(T, \theta)$ due to spherical pins imitating BHO nano-particles and inclined short columnar pins imitating BHO nano-rods by evaluating the dimensions of pinning centers and vortex cores rigorously within a normal-core approximation. We found that $f_{\rm p}(T, \theta)$ tends to decrease with $\theta$ approaching the $B\parallel ab$ direction in some conditions and confirmed that the combination of the angular dependence of $f_{\rm p}(T, \theta)$ and $B_{\rm c2}(\theta)$ leads the anomalous $J_{\rm c}(\theta)$ depression at low $B$ and its crossover to the usual effective mass like $J_{\rm c}(\theta)$ at high $B$. As for columnar pins, we confirmed that the $f_{\rm cp}(\theta\simeq B\parallel c)$ peak becomes broad with shorter columns and successfully reproduced experimentally observed broader $J_{\rm c}(\theta)$ by taking account of the distribution of the inclination and azimuth of short BHO nano-rods.
These results suggest that experimentally observed $J_{\rm c}(T, B, \theta)$ can be basically explained by numerically evaluated $f_{\rm p}(T, \theta)$ and that a prediction of $J_{\rm c}(T, B, \theta)$ based on $f_{\rm p}(T, \theta)$ due pinning centers may be helpful for tailoring the pinning properties of $RE$BCO-CCs depending on applications.
At the conference, we would like to explain our calculations and discuss vortex pinning properties of $RE$BCO-CCs due to spherical pins and columnar pins.
[1] A. Molodyk $et\ al$., Sci. Rep., 11 (2022) 2084.
[2] For example, K. Nakaoka $et\ al$., SuST, 30 (2017) 055008., M. Miura $et\ al$., NPG Asia Mat., 9 (2017) 197.
[3] T. Yoshihara $et\ al$., IEEE-TAS, 33 (2023) 6600205.
[4] T. Okada $et\ al$., IEEE-TAS, 29 (2019) 8002705., T. Okada and S. Awaji, $to\ be\ submitted$.
[5] S. Fujita $et\ al$., IEEE-TAS, 28 (2020) 6600604.
Nonlinear electrical transport is an indispensable tool to study disorder, dimensionality, criticality, and vortex physics for fundamental research on new types of superconductors and technological applications. Because a significant portion of many superconducting phase diagrams occurs at very high magnetic fields ($\it{H}$) only accessible by pulsed field magnets, there is a need to develop non-linear transport capabilities compatible with the stringent challenges imposed by pulsed fields. Among the many technical challenges of performing non-linear electrical transport measurements in pulsed fields, short pulse durations (~50 ms) and large d$\it{H}$/dt values (~10$^{4}$ T/s) are perhaps the most difficult. Large d$\it{H}$/dt values are especially challenging because they generate vortex motion which competes with current induced vortex motion [1]. In this talk, I will show recent developments at the National High Magnetic Field Lab’s Pulsed Field Facility which enable efficient, non-destructive, non-linear electrical transport measurements in pulsed fields. With our state-of-the-art system, we can collect, and immediately analyze, non-linear electrical transport data utilizing the entire field range (55T) accessible within a single pulse [1, 2]. I will present critical current and critical field measurements on YBa$_{2}$Cu$_3$O$_{7-x}$ thin films with different, artificial pinning centers which demonstrate our capabilities, and explore the influence of the irreversibility line on critical currents at low temperatures and in fields up to 65T. Comparisons will also be drawn between the properties of superconducting cuprate thin films and the newly discovered nickelate family of superconductors.
[1] M. Leroux, F.F. Balakirev, M. Miura, K. Agatsuma, L. Civale, and B. Maiorov, $\it{Phys. Rev. Appl.} \bf{\:11}$, 054005 ($\bf{2019}$).
[2] C.A. Mizzi, F.F. Balakirev, B. Maiorov, et al., $\it{In\:preparation}$.
Acknowledgement
This work was supported by the Los Alamos National Laboratory LDRD program, project number 20210320ER. The National High Magnetic Field Laboratory, which hosts the high magnetic field magnets, is funded by NSF Cooperative Agreements No. DMR-1157490 and No. 1164477, the State of Florida and Department of Energy.
Artificial pinning centers (APCs) of varying types and nano-scale size have been successfully introduced into (Y,RE)Ba2Cu3O7-x (Y,RE-BCO, (Y,RE)BaCuO, YBaCuO or YBCO) thin film superconductors by different processing methods in order to strongly and collectively pin quantized vortices. A number of high quality reviews of this large field have been published that describe progress in the fundamental sciences and pseudo-empirical approaches to improving Jc(H,T) and flux pinning properties. Herein a review is provided that focuses on two specific subtopics: i) plotting historical progress world-wide since 1995 increasing Jc(H,T,Ɵ) properties, by data-mining the ~ 87 highest cited papers in the field, and ii) presenting how improvements of Jc(H,T,Ɵ) can have significant impact to improve the performance and capabilities of high power devices and applications. The review plots Jc(H//c,T) values achieved at T = 40K to 77K, and Happl = 0T to 9T, summaries of Jc(H//c,H//ab,min) @65K and 1-3T, and the highest angular Jc(65K, H=1-3T, θ = 0 to 90°). It was found that increases of Jc(H//c,T=40-77K) of 7x to 50x are consistently being achieved by multiple processing methods and nanoparticle additions for the full range of Happl = 0T to 9T. And because of these large increases, it is shown that improving flux pinning at operation temperatures T = 40K to 77K and Happl = 0T to 32T can better enable devices to operate at dramatically increasing higher temperatures, which can significantly reduce system cost-size-weight-and-power (C-SWaP). Reducing C-SWaP can enable operation or completely new capabilities or markets in technology areas such as air or space propulsion.
Acknowledgments. This research was funded by AFOSR LRIR #18RQCOR100, and the Air Force Research Laboratory/Aerospace Systems Directorate.
Electrification of transport is a growing trend. Traction transformers are critical components of Chinese high-speed-trains. Traditional oil-based single-phase 25 kV/1.9 kV traction transformers have a weight of 6 tones, the efficiency less than 94%, and fire risk. The use of HTS has been proposed for compact and light weight traction transformers for Chinese high-speed-trains. The transformers consist of four single-phase HTS windings, operating at 65 K, each of which drives a motor. AC loss in the HTS windings is one of key parameters for the traction transformer application, and in order to achieve the targets of less than 3 tons of transformer system weight, better than 99% efficiency, and 43% short-circuit impedance, AC loss from the transformer windings cannot exceed 2 kW.
In this presentation we show the AC loss FEM modelling results on the traction transformer windings carried out based on both H-formulation and T-A formulation. We investigate the influence of the winding length, asymmetric field – and field-angle-dependent critical current of HTS wires, hybrid winding structure, flux diverters placed near the end part of the windings, the harmonic current components in the low voltage windings on AC loss. With optimized design for AC loss reduction, we discuss the cooling options, total system weight, system component arrangement, and efficiency.
Keywords: Traction transformers, AC loss, H-formulation, T-A formulation, flux diverters, harmonic current components
Acknowledgment
This work was supported by the New Zealand Ministry of Business, Innovation and Employment under the Advanced Energy Technology Platform program “High power electric motors for large scale transport” contract number RTVU2004.
The development of ultrahigh power density rotating machines is a research priority identified by electric aircraft programs worldwide, including ARPA-E, NASA, Airbus, and many others. The reduction of alternating current (AC) losses of all components in rotating machines is critical to reduce to manageable levels, and AC losses can be the dominant factor affecting the machine efficiency and design viability.
This effort is utilizing a recently developed rotating magnet based isothermal calorimeter (SAM) apparatus to measure AC losses at 77K using liquid N2. The system utilizes the stator slot position of a permanent magnet rotating machine, with Bmax ~ 0.58 T in the airgap and dB/dt of up to 240 T/s. A complex 3D environment of B-fields of varying strength, time-varying direction, and harmonic frequencies is achieved, simulating the environment of a real motor or generator. The maximum sweep rates achieved are up to ~ 60 T/sec, which is about ~ 5x higher than typically achieved by other AC loss test systems.
This device has been used to measure the AC loss of many types of superconductors, including YBCO tapes and cables with varying architectures and Ag and Cu thickness, conductor-round-core (CORC), Roebel, and carpet stacks of varying # layers. Metallic and carbon conductors have also been studied including Cu-litz cables with strand filament diameters of 50 μm and 80 μm, ultra-pure Al 99.999+% with varying sheaths and filaments, carbon nanotubes, and others are planned. The experimentally measured losses are compared to theoretical models, when possible. And the impact of AC losses on the power density and efficiency for rotating machines is analyzed.
Acknowledgments: Support by the Air Force Office of Scientific Research (AFOSR) LRIR # 18RQCOR100, and the Aerospace Systems Directorate (AFRL/RQ)
It is well known that screening currents induced in REBCO coils are an annoying phenomenon. Due to the thin tape shape of REBCO coated conductors, the large amount of screening currents are induced, and unexpected magnetic fields are generated. It worsens the magnetic field quality of REBCO magnets by which homogeneous fields are required as applications of NMR and MRI. Recent years, it was pointed out that screening currents cause local overstresses. Hence, the screening current estimation by simulation is very important.
A few screening currents modeling of REBCO pancake coils have been proposed, and these characteristics are different. Our team have also proposed three different modelings: 1) FEM based, 2) network circuit based, and 3) simple circuit based. Accurate modelings need long time, and a fast modeling has less accuracy. To overcome such properties, we have newly developed a fast screening current modeling with sufficient accuracy. In this presentation, we have compared the simulated screening current induced field (SCIF) and the simulation time. The proposed method can accelerate the speed by approximately 6 times by reducing the degree-of-freedom, comparting the FEM based one. When the screening current of 12 single pancake coils, whose turns are insulated, was simulated, the simulate time decreased to 17.5 hours from 105 hours, but the simulated SCIF results are very close. We will show and discuss the hysteresis curve of SCIF when the 12 single pancake REBCO coils are charged and uncharged.
In addition, this proposed model can simulate the screening current of no-insulation (NI) REBCO pancake coils. So far, the FEM based model cannot simulate the screening current without any special technique. By making it circuit-based, it is easy to consider the no-insulation winding structure. Moreover, we pay the attention to the coil voltage during charging.
Acknowledgement: This work was supported by the JSPS KAKENI under Grant 20H02125 and Grant-in-Aid for Scientific Research(S) under Grant 18H05244.
AC losses in conductor-on-rounded-core (CORC) cables of the YBCO High-temperature Superconducting (HTS) tapes represent a significant challenge in HTS power applications. Two Finite Element Analysis (FEA) models were employed to understand the AC loss contributions and provide approaches for reducing AC losses in those cables. The FEA model based on T-A formula treated the cross-section of thin superconducting layers as 1D lines and therefore only can predict the AC loss caused by magnetic flux penetrating from the edge of the HTS tapes (edge loss). The model based on H-formulation can be performed on the actual 2D rectangular cross-section HTS tapes to provide the total AC losses caused by flux penetrating from both the edges and surface of HTS tapes, although this model is much more time and memory-consuming. With the actual thickness of YBCO layers in commercial tapes of about 1.5 µm, the T-A model underestimates AC loss by about 5% to 20%, depending on the gap between HTS tapes in the cable. That model, therefore, was used intensively to study effect of cable geometric configurations and operational parameters on AC losses of two-layer CORC cables. The models were also used to calculate the eddy-current losses in normal metal layers of HTS tapes which could play an essential role in high-frequency HTS power applications.
Rare-earth barium copper oxide (REBCO) coated conductor can be fabricated into Roebel cable for the realization of larger stored energy high field magnets. There are two factors, current sharing and ac losses, that are critical to the stability and quench protection of the high field magnets and cables. Those two factors are strongly dependent on inter-strand contact resistance (ICR) of the cable. The ICR for as received cable/tapes can be as high as 17076 Ωcm2. By applying different treatments, such as compression, heat treatment, and surface modifications, we are able to achieve the ICR value from 100 Ωcm2 to 2.7 Ωcm2 to allow better current sharing. On the other side, lower ICR leads to higher AC loss. In this work, magnetization ac loss of a Ni-plated Roebel cable which has an ICR of 2.7 Ωcm2 is measured using an M-H loop method in a liquid nitrogen environment (77 K). The magnetic field is generated with a race-track copper magnet with magnetic field amplitude ranging from 4-70 mT and frequency range of 50-200 Hz. We compared this to analysis to explore the role of the cable and conductor magnetic permeability on the extracted resistivity. Then the cable magnetization was measured under 4.2 K with a 12 T magnet system which has a maximum ramp rate of 3.77 mT/s. Then the flux creep analyses were performed by holding the applied field at 1 T for 1800 s. Results from magnetization analyses can be used in error field correction of high field HTS magnets for particle accelerator applications.
This study presents a finite element method (FEM) analysis of magnetization AC loss in REBCO coated conductor tape and helical wound tape conductors. AC loss is a significant factor that limits the practical application of superconducting cables and coils, and it is crucial to accurately predict and minimize the loss for the practical application of superconducting systems. The FEM analysis was carried out using the commercial software package COMSOL Multiphysics, which can accurately simulate the AC loss behavior in superconductors. The simulation model was compared to analytic models and to previous experimental results. The simulation results calculate both the hysteretic and individual tape eddy current loss. We simulated a flat tape in a perpendicularly applied field of magnitude 0.5 T and a with a sinusoidal oscillation in time. Our second simulation was to the same tape, but with a field that varied along the tape width sinusoidally as well. Finally, we modeled a helically wrapped tape in a field applied along the helical axis. We used a diluted superconductor approach for the FEM modeling. Various twist pitch values were explored, and the results were compared to the analytical expectation of loss reduction by 2/Pi from that of flat tapes in fully perpendicular fields.
The magnetocaloric effect is a phenomenon where certain materials change temperature when exposed to a change in magnetic field. This adiabatic temperature change in temperature at or below a magnetocaloric material’s Curie point can be combined with heat transfer fluid flows to perform refrigeration cycles such as the Active Magnetic Regenerative Refrigeration cycle (AMRR). Detailed analysis of magnetocaloric liquefiers shows it is possible to increase the efficiency (FOM) of small industrial-scale liquefiers (10-30 tonne/day) of liquid cryogens by 50-80% over comparable conventional liquefiers. For several years we have been developing lab-scale prototypes to validate this potential. One device that spans from 100 K to 20 K utilizes a reciprocating dual-regenerator design with three magnetic refrigerants in each regenerator. This assembly is linearly axially moved in and out of a 6.5 T solenoidal superconducting conduction-cooled magnet with two reversing heat transfer fluid flows to execute the four-step AMRR cycle. During this cycle, one of the regenerators executes a heat rejection step while magnetized, and the other absorbs a cold thermal load while demagnetized. Inherent to the AMRR cycle, the magnetization (A/m) of the refrigerants is temperature dependent such that the demagnetized regenerator cools which increases its magnetization while the magnetized regenerator warms which reduces its magnetization as they synchronously move in or out of the field. There is a large magnetic force (toward the high-field region of the magnet) on the magnetic refrigerants as they are moved out of the magnet. Correspondingly the other dual regenerator experiences a slightly smaller magnetic force toward the high field region of the magnet as it moves into the magnet. These opposite attractive forces react against each other, but the net difference in magnetization results in a net force imbalance during the reciprocating movement of the regenerators. The work input required to complete the cycle is the work input for the AMRR cycle. The magnet is put in persistent mode after it is charged to the current required for the desired magnetic field strength H and empty magnet flux density. The magnetic refrigerants also contribute to the magnetic flux density B. In persistent mode the magnet becomes a constant flux device so when there is a change in magnetization inside the bore of the magnet as the regenerators are moved, the free current in the magnet must also increase or decrease to keep the flux constant. The changes in free current in the magnet windings cause flux jumping which causes Joule heating in the Cu stabilizer or AC losses. In earlier prototypes the total mass of the regenerators was about 100 grams. The AC losses in these prototypes were only a few tenths of a Watt so the two-stage 1.5 W @ 4 K GM cryocooler easily kept the magnet at or below ~4.5 K. As we increased the temperature span and cooling power, the regenerators had several layers of refrigerants each with different mass with a total mass of a few kg. During our test runs with the first of these prototypes we found that the heating in the magnet was much larger than due to AC losses causing the coil temperature to rise over 4.8 – 5 K in as few as ten refrigeration cycles at 0.25 Hz. This was a puzzle that we solved using COMSOL Multiphysics with the AC/DC module. The detailed drawing of the dual regenerator assembly with all different magnetic properties was used to calculate net magnetic forces between the refrigerant masses and magnetic field during the reciprocating cycle. These results showed the force imbalances were caused by the geometry of the dual regenerator assembly with non-magnetic gaps between refrigerant masses. This paper describes the unexpected mechanisms that caused the excessive heating in the magnet and the results of an innovative experiment we did to validate the COMSOL predictions and convincing show what the caused the magnet heating.
New Zealand companies have long been recognised as a global leader in renewable energy integration and holding deep expertise in commercial application of superconducting technology. This is supported by the New Zealand government who have put in place a strategy that mirrors this; to be net carbon-zero by 2050. The government have further invested in cooperative technology development programmes that will accelerate international development.
Transportation is the largest source of our non-agricultural greenhouse gas emissions from the country – domestic aviation accounts for 10% of our emissions and long-haul travel maybe more. We depend on aviation, our exports depend on shipping, and our internal freight relies on trucks. We will use electrical energy to reduce our carbon footprint. The good news is that New Zealand is unique in its electricity production – over 80% of our electrical energy is generated from renewable sources, and we are targeting an increase to 100% using wind, solar, and geothermal energy. We have the opportunity for truly zero carbon electrical energy to power this revolution.
Electrification of aviation propulsion has the highest potential of drastically reducing emissions in a sector that is critical to New Zealand prosperity. Our domestic (Sounds Air) and international (Air New Zealand) are both committed to passenger electric flight introduction by 2026. The NZ government are supporting this and making the regulatory framework available to act as an international test-bed. This is driving significant commercial partnerships both within NZ and with overseas manufacturers.
We see large transport is the challenge for electrification - aircraft with more than 100 seats. Conventional technology cannot provide the power-to-weight required to electrify at this scale. Superconducting, and cryogenic, machines may provide a solution: they are small and light, relative to their power output. New Zealand has been working on superconductors since the 1980s and researchers in this field have recently teamed up with NZ’s leading researchers in power electronics and cryogenics systems, and formed strategic international research partnerships.
We will present an overview of the multidisciplinary research in this NZ national programme towards electric flight realization. We will examine the technology integration within superconducting machines for aircraft using novel technology such as flux pump exciters, low ac-loss windings, additive manufacturing wide bandgap electronics and integrated cryogenic systems. We will present an overview of the technology development, implications and how this research is globally relevant. We will report on results from a superconducting motor that has been operated at 18,000 rpm and highlight the way forward.
Acknowledgment
This work was supported by the New Zealand Ministry of Business, Innovation and Employment (MBIE) under Strategic Science Investment Fund “Advanced Energy Technology Platforms” contract RTVU2004.
Keywords: superconducting machines, electric aviation, cryo-electronics, cryocooling
IBM announced the fabrication and initial characterization of its 433 qubit Osprey processor in late 2022, and released it to clients in 2023. Osprey required several advances to yield a payload nearly 4x larger than its predecessor, Eagle (127 qubits). In addition to developments in the payload, Osprey is the first IBM quantum system to involve significant changes to cryogenic infrastructure, primarily the introduction of flex cable wiring. I will discuss the important factors in designing a wiring scheme, the specific advantages of flex wiring versus traditional coax, and the additional advancements to wiring and cryogenics needed to scale for future systems outlined in IBM's quantum development roadmap https://www.ibm.com/quantum/roadmap.
Advancements in electronic technology with cryogenic operational temperature requirements call for the study of thermal properties of the materials used to connect the heat source and cooling system. A test facility was developed to investigate thermal properties important to these applications--bulk conductivity and contact resistance--for a temperature range of 4K - 40K. Bulk conductivity tests were conducted on OFHC copper sourced from three different commercial vendors to determine any variation between both the commercial sources themselves and to the values found in literature. Preliminary analysis found RRR values within the range of 50 to 75 for all sources examined. These results are in line with previous studies and confirm the consistency of conductivity regardless of the source. The contact resistance tests focus on the variation of applied force; a uniform force ranging from 90N - 245N was applied to gold-plated OFHC copper samples with surface roughnesses between 1-2 micrometers. Results from these tests will highlight the significance of force variation. The results from both tests will help guide the design of heat paths in future cryogenic electronic technology.
Dragonfly is a planned rotorcraft mission that NASA/APL will be sending to Saturn’s moon Titan to study its chemistry. The Dragonfly Mass Spectrometer (DraMS) is a mass spectrometer that is being developed to identify different kinds of organic material that comprises Titan’s surface. The Cryogenic engineering team on DraMS is developing and interface between the room temperature rotorcraft body and the near-cryogenic temperatures of an onboard sample chamber, while minimizing the thermal leak to the Titan environment. As part of design process, the Cryogenic team has built a conductivity test rig for testing the thermophysical properties of candidate insulators, which includes Rohacell 31HF and hollowed 3D printed PEEK structures, at simulated Titan environmental conditions.
The article presents the optimization of the power density of a thermoelectric generator (TEG) operating in cryogenic temperature conditions. Optimization of TEG power density was performed as a function of TEG leg length and its effect on TEG performance. The coefficient of merit (ZT) of the TEG was experimentally verified for the temperature range of a cold sink from 160 to 250 K, which corresponds to the temperature of the wall subjected to the boiling film of LNG. The numerical model proposed in the article was verified by comparison with experimental data, and then used to simulate the operation of the TEG at a cold sink temperature of 100 K corresponding to the wall temperature in the process of LH2 regasification. The obtained results showed that the optimal length of TEG legs is less than 10 mm and depends on the boiling and heat transfer regime. The results of the presented research can be used to improve the effectivity of cold exergy recovery from cryogenic systems.
This study introduces a novel ice lithography system integrated with a low-vibration micromachined Joule-Thomson cooler. Ice lithography is an eco-friendly method for high-resolution nanofabrication on delicate substrates and requires to operate below 130 K in the vacuum of a microscope chamber. Previously, liquid nitrogen rather than cryocoolers was used to cool the system due to its low vibration, but it is both bulky and costly. To overcome these challenges, this study employs a low-vibration micromachined cooler in a scanning electron microscope (SEM) for ice lithography. The design and methodology of the system are described in detail. The results show that the substrate can reach a temperature of 105 K within 30 minutes with a measured mechanical vibration of less than 10 nm, enabling high-resolution nanofabrication. As proof of concept, the system successfully fabricates nanoscale patterns on a silicon chip. This low-vibration cooling system has great potential for use in cryo-EMs in the future.
The ITER’s Cryoplant occupies nearly 8000 m2 area composed of various cryogenic systems aimed at the production, liquefaction, and storage of cryogenic products. Transferring of cryo products occurs by cold and warm lines with a total length of 1.5 km within the Cryoplant area and 3.5 km in the Tokamak building to gradually cool down in total 10000 tons of ITER superconducting magnets, thermal shields, and cryopumps with the following maintaining 4.3 K during plasma operation state. After the successful completion of the construction and pre-commissioning phases, the Cryoplant is currently active in the commissioning phase with by now several commissioned systems including confirmed performance and the integration of automatic control to support the launch of the next systems. This paper reports on a detailed overview of the completed phases, starting systems, control implementation, and performance tests, including planned activities for 2023/2024.
Liquid nitrogen is often used as a substitute for oxygen testing due to safety concerns, and the general similarity between their fluid properties. During the Cryogenic Fluid In-situ Liquefaction for Landers (CryoFILL) testing, an opportunity arose to compare liquid nitrogen and liquid oxygen behavior using the same test hardware in similar test conditions. Comparative testing would verify whether the system response to nitrogen and oxygen would behave in a similar manner. Tests that were investigated include system boil-off heat load determination, autogenous pressurization, cryocooler loop initiation, and cryocooler loop operations. Results from testing are shown and compared to verify that liquid nitrogen and liquid oxygen tests yield similar system responses, and that nitrogen can be used as a substitute for oxygen in developmental tests at cryogenic temperatures.
The High Luminosity LHC (HL-LHC) project is aiming to upgrade the Large Hadron Collider (LHC) at CERN by increasing its peak luminosity by a factor of five with respect to its nominal value. This upgrade will include the replacement of the final focusing superconducting magnets and additional superconducting radiofrequency crab cavities in the long straight sections of the interaction points 1 and 5 of LHC.
The cryogenic heat loads in points 1 and 5 of the LHC accelerator will significantly increase, mainly because of the higher luminosity. Therefore, two new refrigerators will be required in points 1 and 5, with each an equivalent capacity of 14kW@4.5K, including 3.25kW@1.9K.
This paper presents the functional requirements and conceptual design, the key choices and specific challenges including the civil engineering constraints and the major technical requirements detailed in the Technical Specification documents for the supply from the European industry of two new helium Refrigerators for HL-LHC. A procurement contract based on this specification, was placed in 2022.
The experimental system for the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) has several segments. Following the acceleration through the three superconducting Linac segments, the heavy ion beam is guided through the target, a fragment pre-separator and (the A1900) separator segments. It can then be split and sent to various experimental vaults and instrumentation, e.g. S800 spectrograph, and the newly proposed High Rigidity Spectrometer (HRS). Presently, superconducting magnets at the target and fragment pre-separator segments, along with the Linac superconducting cryo-modules, are supported by FRIB’s main helium refrigerator. The remainder of the cryogenic loads are supported by the legacy NSCL Cryogenic Refrigerator (a re-commissioned Bureau of Mines helium liquefier from the 1970’s). Considering the operational stability of the accelerator, and maintainability of the entire cryogenic system at FRIB – it is logical to segregate the experimental system loads from the accelerator system loads. A new cryogenic refrigerator is planned to support the nominal operation of the experimental system loads, and stand-by (4.5 K) operation of the accelerator system loads during main refrigerator maintenance. This new refrigerator is planned to be able to support a combination of 4.5 K isothermal refrigeration, 4.5 K liquefaction and a non-isothermal 60 K thermal shield load. The thermodynamic process cycle design for this cryogenic refrigeration system is discussed, and its theoretical performance characteristics under various load conditions are studied. This paper outlines the findings from this process study and the key selection parameters for the major components, such as the warm compressors, turbo-expanders and heat exchangers.
Cryogenic Systems require a highly efficient insulation so as to limit the heat ingress and boil-off, which is generally achieved through the use of vacuum combined with an insulated media. The performance of two families of vacuum insulated technologies, Multi layer Insulation (MLI) and Microspheres (MS), will be investigated with detailed thermal models developed to account for all the heat transfer contributions, solid conduction, gaseous conduction and radiation. Results are presented for an usual cold vacuum pressure (CVP) corresponding to high vacuum (<10-6 mbar) and compared with available experimental measurements for state of the art technologies. The nominal thermal performances are then evaluated for a cold temperature of 20K (representative of liquid hydrogen storage temperature), for a degraded CVP with hydrogen and air as residual gases and for increased hot boundary temperatures. A sensitivity of the thermal performance is also presented with a pressure gradient through the insulation thickness, induced by cryopumping and materials outgassing. Finally, other parameters are also discussed such as, for MLI family, the number of layers, material, layers density, venting options, assembly process and material optical properties; and for MS family, the density, the mean particle size, their properties and distribution.
Hydrogen because of its zero carbon emissions and highly energy-dense nature has a strong potential to be used as an aviation fuel. One of the ways of using hydrogen in aircrafts is to store liquid hydrogen in cryogenic tanks on board and then vaporize and mix with air before being burned in the combustion chamber. But a major challenge with cryogenic hydrogen storage is the dynamic movement of the fuel which can lead to fuel boil off and bubble formation. In the current paper, the sloshing motion of liquid hydrogen in a CHEETA type thin-walled composite fuel tank, under acceleration data obtained from an Airbus A-320 in cruising conditions, is investigated. The dynamic fluid structure interaction problem is solved numerically using the Coupled Eulerian-Lagrangian (CEL) technique in ABAQUS. The developed modelling strategy is then employed to study the impact of various internal baffle designs on the sloshing behavior of the fuel under different fill levels. This study not only establishes that sloshing is a major cause for concern when it comes to liquid hydrogen aircraft fuel storage, but also advances our understanding in devising potential mitigative strategies.
Keywords: Fuel sloshing, Fluid structure interaction, Coupled Eulerian-Lagrangian, Liquid hydrogen fuel, Net-zero carbon aviation.
Acknowledgement: Authors gratefully acknowledge support for the Center for High-Efficiency Electrical Technologies for Aircraft (CHEETA) by NASA under Award 80NSSC19M0125.
Insulation systems are critical to liquid hydrogen storage tank thermal performance. Storage tanks in the capacity range of 100 to 1,000 cubic meters are typically shop built and designed with evacuated multi-layer insulation (MLI), whereas storage vessels larger than 1,000 cubic meters are typically field-erected and supplied with evacuated bulk fill insulation. Field-erected vessels use bulk fill insulation because MLI installation is impractical in the field and requires a controlled shop environment to achieve the optimum cleanliness level needed. MLI systems require high vacuum (HV) to fully utilize the insulating properties, while bulk fill systems only require moderate vacuum (MV) for full effectiveness. For large field-erected vessels, the two types of bulk fill insulation available are perlite and glass bubbles. The selection of either material is driven by a tradeoff between CAPEX and OPEX, such as the construction cost versus operating thermal performance and maintenance. In either case, the vacuum level needed to achieve optimum thermal performance is likely to drive the field testing and commissioning portion of the construction schedule. The goal of this paper is to present practical experience and standard data for both warm vacuum pressure (WVP) and cold vacuum pressure (CVP) levels. Recommended WVP levels needed for cooldown of large-scale liquid hydrogen storage tanks consider both perlite powder and glass bubbles. The pumping time expected to achieve the target vacuum level, considering insulation filtering, vacuum pumping equipment, pipe sizes, and installation requirements, is also discussed. Recommendations for a standard practice in vacuum-jacketed tank commissioning are based on historical NASA data, and those collected during recent projects completed at Kennedy Space Center and in Houston, Texas.
Cryogenic tank chill and fill is an important cryogenic fluid management (CFM) technology that supports and enables many of NASA’s long-duration space missions. For no-vent fill, the receiver tank pressure remains below the supply tank pressure during the entire duration of the fill so that the tank does not require venting. This is especially advantageous for tank fill operations in low gravity where the position of the liquid is not always known and venting the tank may cause loss of propellant by venting liquid. In lieu of expensive tests conducted on-orbit, accurate computational models capable of predicting receiver tank pressure during cryogenic propellant tank fill may be used to reduce system and propellant mass as well as mission risk. However, these numerical models must be validated or anchored to test data. This study presents a computational fluid dynamics (CFD) model with conjugate heat transfer that is used to predict a liquid hydrogen tank chill and no-vent fill ground test conducted at Lewis Research Center (now Glenn Research Center) in 1991. The specific test case chosen for model validation implemented an upward-facing jet near the bottom of a cylindrical 34 liter tank. CFD predictions are compared to experimental measurements of tank pressure, fill level, fluid temperatures, and wall temperatures. The CFD results show reasonable agreement to the test data but overpredict the pressure collapse near the end of the fill despite the liquid jet penetrating the liquid-vapor interface. Several sensitivity studies are considered due to notable uncertainties in the experiment.
As the hydrogen market expands, the need for efficient distribution of liquid hydrogen (LH2) becomes more important. On the one hand, there is a need to reduce flash gas losses during the transfer of LH2. On the other hand there is often a demand for pressurisation of LH2 to overcome transfer losses or to meet minimum input pressure requirements of downstream applications like fuel cells or combustion engines. It is therefore essential to develop pumps for liquid hydrogen. Consequently, a test rig is necessary to characterise their behaviour. In order to perform continuous measurements with a comparably small amount of liquid hydrogen it is designed as recirculation loop. The development of a submersible pump involves multiple engineering related challenges. This paper presents the general concept of a submersible liquid hydrogen pump and discusses several design decisions. It also gives an insight into the built test rig and its capabilities and instrumentation.
Several studies have demonstrated that Reverse Turbo-Brayton cryocoolers could be the next space cryogenic revolution, thanks to their capability to provide vibration-free remote cooling in the temperature range of 4 to 150K and for medium to high cooling powers. In this framework, Absolut System developed a Vibration-free 40-80K Reversed Turbo-Brayton cooler, work performed under contract N°XXXX and funded by ESA. The cooler is based on two turbo-compressor stages, a high efficiency recuperator and a cryogenic turbo-expander, for operation between 300 and 40K.
Following the fabrication of the cooler, we performed tests on both individual components, compressors, expander and recuperator as well as on the complete cooler. The turbomachines use aerodynamic bearings and generate very little vibrations and are extremely resilient. The characterizations performed during the project concern exported micro-vibration behaviors of the compressors and the expander, operating respectively up to 250,000RPM and 150,000RPM, and thermodynamic performances of the different elements. The cooler was tested down to its minimum temperature and required the development of specific operating procedures with regards to the conditioning of the circuit.
We report here in a first part the main results and observations stemming out of the test campaigns carried out during the project.
This work showed the necessity of putting additional efforts on the recuperator, one of the most critical component of the cooler. Absolut System is thus also working in parallel on developing a very high efficiency and compact heat exchanger for the specific needs of Turbo-Brayton Coolers in response to the ESA Proposal ESA-TDE-TECMTT-SOW-023649.
The technology selected for this is based on the common tube and shell but using very thin tubes of small diameters (<1mm). The challenge of this exchanger is not only the manufacturing, but also the very strict requirements. Obtaining a >97.5% efficiency in a very small mass while maintaining very low pressure drops, makes for a very compelling project.
We have performed the design phase, tested, and validated different aspects of the assembly. The design for the first breadboard model has been validated numerically and is in the fabrication process. Testing the exchanger will then take place to characterize the performances of the recuperator and allow for a comparison between experimental results and analytical and CFD models.
All these tasks are participating in placing the Turbo-Brayton cryocoolers at the forefront of space coolers and this development is pushing Europe even further in State of Art advancements for space, and brings us all closer to fulfill future Space Explorations and Earth Observation missions.
Sumitomo Heavy Industries, Ltd. (SHI) supplies 4K-class and 1K-class cooler for space use. The 4K-class and 1K-class cooler consists of Joule-Thomson(JT)cooler and two-stage Stirling cooler as a pre-cooler . To improve cooling capacity of 4K-class and 1K-class cooler, we are developing the cooling capacity of two-stage Stirling cooler below 20K. The performance of the two-stage Stirling cooler essentially depends on the volumetric heat capacity of its regenerator. We investigated new materials which has higher volumetric heat capacity than stainless steel used in current model , and succeeded improve the cooling capacity of the two-stage Stirling cooler. This paper describes the numerical estimation and the results of cooling tests of the two-stage Stirling cooler using new materials.
Northrop Grumman Space Park (NGSP) introduced the MiniCoolerPlus (MCP) to its family of pulse tube cryocoolers in 2019 and presented the details of its TRL6 qualification testing in 2022. The thermal mechanical unit (TMU) of the MCP is an extension of space-qualified pulse tube coolers, all of which are designed to provide a long life (ten-plus years) of delivering low-mass, high-cooling capacity for hyperspectral and infrared imaging payloads in tactical airborne and space applications. The cooler is of modular split configuration allowing flexibility in the compressor (wave generator) and cold head placements in order to meet the available envelope of packaging constraints. The cold head assembly can be oriented at any position relative to the compressor assembly, and the transfer line (length and shape) can be customized to individual applications. The TMU weighs less than 3kg and can lift 1.5 W at 45 K or 11 W at 110K with 150 W electrical input at 300 K reject. The thermal performance has been characterized as a function of input voltage and as a function of cold tip load and temperature at a variety of heat sink temperatures of -20C, 0C, +20C and +40C. Functional testing of the MCP was performed to higher input powers and MCP impedance versus operating conditions were collected. An analytical expression for cold tip load (Qc) and impedance (Z) as a function of reject temperature (Trej), cold tip temperature (Tc), frequency (f), and input power (Pac) were generated. These tests were conducted with third party control electronics and the results will be presented here.
An Air Liquide large pulse tube cryocooler (LPTC) was parametrically performance tested for cold tip temperatures between 40 K and 200 K and heat rejection temperatures between 0°C and 40°C. The testing utilized a single off-the-shelf power supply to drive the compressor motors in parallel. The effect of compressor temperature and pulse tube inclination angle are also presented. In addition, the exported forces were measured at ambient conditions and the results are shown and discussed.
Two Thales LPT9310-HP commercial off-the-shelf (COTS) cryocooler were parametrically performance tested for cold tip temperatures between 50 K and 250 K and heat rejection temperatures between 0°C and 40°C. Both coolers had identical transfer line configurations. The test results revealed unit-to-unit thermodynamic performance variation and are compared to test results of a COTS LPT9310 cooler with the same transfer line configuration. The effect of compressor temperature and pulse tube inclination angle are also presented. In addition, the thermal performance was found to be similar for COTS cooler drive electronics and an AC power supply.
Over the past 5 years, Ball Aerospace working with teammates that include Sunpower/Ametek, Iris, and SDL and sponsored by both internal and external customers, has developed a product line of low cost, low EFT, high capacity, high reliability cryocooler systems. A key element is the high efficiency, long life, low cost Sunpower cryocoolers. Specifically, the products include the DS-30, DS-10, and DS-Mini coolers. Ball has augmented these coolers by integrating them with several EFT and launch vibration attenuating platforms. Additionally, these systems can drive the coolers with either an Iris CCE or a Ball MACCE. The result has been a flight qualified product line of cooling systems that compared to traditional space coolers are 2-5X lower cost, 10-40X lower EFT output, 3-5X higher capacity and efficiency. These cooler products have been delivered for several flight programs.
To support the application of heritage aerospace coolers and modern tactical coolers to future mission architectures, Ball has developed the Modular Advanced Cryocooler Control Electronics (MACCE). This entirely new cryocooler electronics architecture is based on modularity and scalability in performance supporting a wide range of cryocoolers including 4K Hybrid Systems (J-T + Pre-Cooler), Pulse Tube Cryocoolers, and Stirling Cryocoolers. The MACCE design includes the primary CCE box and an Accelerometer Pre-Amp (APA) box that can be remote mounted. The MACCE architecture includes four high power drive channels and two low power channels supporting >500W of output power, three independent accelerometer feedback control loops for vibration cancellation, high efficiency using GaN FET technology, and a combination of six thermistors and six precision RTD circuits for telemetry. Operational modes include constant power, constant temperature, or open loop. An engineering model of MACCE has been completed and is currently going through qualification. Performance data is presented from box level testing.
The explosion in earth and space observing satellite developments has led to a need for a broad range of cooling solutions for the associated imaging sensors. Cooling is generally provided by thermo-mechanical cryocoolers. Driving and controlling cryocoolers requires specialized power electronics that provide both power and control to the cryocooler, these electronics are called Cryocooler Control Electronics (CCE).
Since the cooling power the cryocoolers are required to provide varies over a large range, the requirements of the associated CCEs also vary widely. For instance, CCEs supporting this range of missions vary in output power from 30 watts to more than 500 watts.
In this presentation, Iris Technology will discuss our ICE-G (Iris Control Electronics with GaN FETs) series of CCEs. The ICE-Gs all share the same processing core but have specialized power handling circuits depending on the output power required. Using GaN FETs increases CCE efficiency, decreases CCE cost, and reduces CCE weight when compared to MOSFET solutions.
For several years Iris Technology has been developing a new line of cryocooler electronics (CCE) based on higher-efficiency GaN FET power transistors and reprogrammable microcontrollers. This product line has been growing, starting with a 30-watt unit several years ago, then the 60-watt version, and last year extending to a 200-watt model. In this presentation, we will introduce a new model that addresses the up to 600-watt class of cryocoolers.
Quantum computing is a fast-developing field pursued by many academic groups as well as industry R&D centers. I will give a short overview of the current state-of-the-art superconducting qubit-based quantum computing efforts at IBM using our Condor quantum processor development as an example, followed by revealing glimpse of project Goldeneye - the first quantum-ready large cryogenic concept system to support Condor-like quantum processors.
As part of the efforts of the Superconducting Quantum Materials and Systems National Quantum Center at Fermilab, we will construct a large millikelvin refrigeration platform known as Colossus. The Colossus platform will be used for quantum computing applications, along with physics and sensing experiments. At the preceding CEC/ICMC meeting in 2021, we reported on the conceptual design of the platform. In the intervening time, the design of the system has been completed and passed through review, with construction now underway. This paper provides an update on the overall design of the system, and the status of and timeline for construction.
Peter E. Bradley1, Elizabeth Sorenson1,2, Damian Lauria1, Li-Anne Liew1
1National Institute of Standards and Technology, Colorado, USA
2 University of Colorado at Boulder, Colorado, USA
Micro Electro Mechanical Systems (MEMS) switches possess many advantages over their bigger conventional counterparts, such as much smaller size, weight and power consumption. Being able to operate MEMS switches at cryogenic temperatures is critical for replacing conventional switches in superconducting circuits, which drive a range of applications from high-speed telecommunications to quantum computing. Implementing MEMS in a product or application can be cost-prohibitive, however, because in-house MEMS fabrication requires expensive precision tools, a highly controlled environment or “cleanroom”, manpower to carry out the highly skilled labor-intensive fabrication and maintain the fabrication facility, and expertise in MEMS design and process design. These factors make MEMS components out of reach for many academic research programs and small companies. Alternative, commercial MEMS foundry services are also expensive and also require in-house MEMS design expertise. Therefore, commercial off-the-shelf MEMS devices play an important role in commercialization of the above cutting-edge technologies. However, commercial MEMS switches are designed for ambient conditions and as such there is little/no data available regarding their operation and performance at cryogenic temperature near and below 4 K. Research in the academic literature has focused on custom MEMS switches fabricated with exotic materials and more elaborate fabrication process, however, long-term cryogenic operation and repeated thermal cycling are still known to limit the device lifetime. Furthermore, because the commercial MEMS switches come fully packaged inside sealed housings which cannot be easily removed nondestructively, inspection of the switches accumulation of material/structural damage, which can alter the switches’ operating characteristics, is not feasible. We are therefore developing the testing methodologies and system to evaluate the structural reliability of commercial off-the-shelf fully packaged MEMS switches for cryogenic applications, with a focus on quantum computing. Our test methods consist of DC and low-frequency tests which are informative of the switches’ structural reliability, conducted at room temperature down to ~15 K. In this paper we present ambient performance data and cryogenic data for temperature below 80 K down to about 15 K. We also present information regarding the development of the repurposed GM-type cryostat to perform these characterizations. This data will inform our understanding of the commercial MEMS switch reliability and provide guidance for switch damage-mitigation strategies during implementation in advanced cryogenic application such as quantum computing.
Key words: cryogenic, MEMS - Micro Electro Mechanical System, MEMS switch, structural reliability
Peter E. Bradley, pbradley@nist.gov
Elizabeth Sorenson, elizabeth.sorenson@nist.gov
Damian Lauria, damian.lauria@nist.gov
Li-Anne Liew, li-anne.liew@nist.gov
Niobium is a widely accepted material for quantum computing device as well as superconducting radio frequency (SRF) technology. Superconducting niobium is a marginal type II superconductor which has a very narrow gap (~20-30 mT) of the mixed state at 2K, even showing the intermediate state (IMS) at the early stage of magnetic vortex penetration. Tremendous progress has been made in understanding the impact of the Nb surface and bulk superconductivities on SRF resonator performance. However, the effect of thin superconducting Nb films for quantum computing applications requires further examination. In this study, we explore the fundamental superconducting properties of various thin Nb films and compare them with respect to the energy relaxation time, T1, measured from superconducting qubit fabricated with these films. The Nb films are fabricated both with or without a surface protective layer that prevents the formation of lossy Nb2O5. Electromagnetic properties are characterized by means of bulk magnetization, electromagnetic transport, and dynamics of surface superconductivity. In addition, analytical electron microscopy is implemented to further connect the superconducting properties to microstructure.
ReBCO cables are of increasing interest for HEP dipole and quadrupole magnet inserts. Cables are typically desired for both current sharing and redundancy as well as inductance minimization. In this work we explore the effect of round configuration REBCO cables (e.g, CORC or STAR) on field error in cos theta and canted cos theta insert magnet designs. We present magnetization measurements on existing CORC and STAR cables, and then use analytic models to predict the magnetization and penetration fields of cable variants (e.g., different strand numbers, different cable Ic values). These models can be fed into finite element treatments that treat the conductor as a magnetic material, this leads to field error predictions. We obtain b3 values of several hundred units in some cases, but there is a strong impact of the field cycle and the penetration field on the results. Current sharing in cables is also considered, and values of ICR to allow acceptable current sharing under various thermal boundary conditions discussed. Based on these values, we estimate the variation of the additional contribution to cyclic AC loss in the accelerator with various levels of interstrand contact resistance; this is compared to the cyclic hysteretic loss.
The wide, 4 mm typically, the monofilament shape of a usual coated conductor causes large magnetization, which could deteriorate the field quality of an accelerator magnet. If we filamentize a coated conductor and insulate its filaments one another, we can reduce the magnetization of the coated conductor. However, such a coated conductor, in which no current can be shared among filaments, is not practical, considering that defects localized longitudinally and laterally are unavoidable in any coated conductor. Just one local defect in each narrow filament could block its current, and, then, a long coated conductor consisting of such filaments cannot carry any current, i.e. its end-to-end critical current could be zero. If we plate the entire group of filaments with copper, the copper could allow current sharing to improve the robustness against local defects. Similar to low Tc superconductors in which filaments are embedded in copper, note that the assembly of filaments (a coated conductor) must be twisted to decouple filaments electromagnetically against transverse magnetic fields. Otherwise, filaments coupled electromagnetically behave like a monofilament coated conductor, and the magnetization cannot be reduced. However, we can easily imagine that twisting a tape-shape coated conductor is far from practical. We have been proposing winding spirally a copper-plated multifilament (striated) coated conductor on a round core instead of twisting it. The spiral geometry plays an equivalent role to the twist geometry in order to decouple filaments. We wound spirally copper-plated coated conductors on a core in multiple layers to form a cable, which can carry a high current. We name this cable SCSC cable, standing for Spiral Copper-plated Striated Coated-conductor cable. We measured magnetization losses using short samples to confirm that the coupling time constants could be reduced by spiraling and that the magnetization losses could be reduced. We also confirmed that a four-layer cable sample could carry a reasonable current, which was equal to the sum of the critical currents consisting of the cable sample. A reel-to-reel cabling machine was installed at Kyoto University, and, now, we can fabricate long cables using it. The latest results of the research and development of the SCSC cables will be reported in the presentation.
This work was supported by JST-Mirai Program Grant Number JPMJMI19E1, Japan.
Iron-based superconductors (IBS) are very promising candidates for high-field magnet applications owing to their ultrahigh upper critical fields and very small anisotropy. In recent years, tremendous progress has been made on the critical current density (Jc) of IBS wires and tapes based on a powder-in-tube technique, e.g., high transport Jc up to 2.2×105 A cm-2 at 4.2 K and 10 T was achieved in 122 type IBS tapes. Furthermore, the transport Jc of IBS tapes with high-strength composite metal sheath such as Cu/Ag and Stainless steel/Ag was enhanced above 105 A cm-2 at 4.2 K and 10 T as well. On the other hand, with hot isostatic pressing process, the Jc-performance of IBS round wires was also significantly improved. With the achievement of high-performance multifilamentary IBS long-length tapes, the first IBS single pancake coil and double pancake coil were fabricated and tested at 24 T and 30 T background field, respectively. Two IBS racetrack coils using 100-meter long IBS tapes were successfully made and tested in a superconducting dipole magnet which provided a maximum background field of 10 T at 4.2 K. These results demonstrate the great potential of IBS wires in high-field accelerator applications.
Next-generation high-energy accelerators like SPPC or FCC need thousands of accelerator magnets with the field strength of 16-24 T. Advanced high-field superconducting materials with significant lower cost and better mechanical properties will help improve the feasibility of such projects to a reasonable level. Since 2008, iron-based superconductors (IBS) have been discovered and attracted wide interest for both basic research and practical applications, which has a high upper critical field beyond 100 T, strong potential current carrying capacity and much lower expected fabrication cost. IHEP and IEE started collaboration in developing high field magnet technology with IBS materials in 2018. The 1st IBS solenoid model coil was fabricated and tested at 24 T background field in 2019; the highest current of IBS model coil has reached 60 A at 32 T recently. IHEP also fabricated several racetrack coils with 100-m long IBS tapes; the quench current at 10 T reached over 80% of its quench current at self-field. Moreover, a 1.3 kA IBS transposed cable has been successfully fabricated and the high field performance is being tested; a new cable with the critical current of over 5 kA is to be fabricated and tested in 2024. An overview of IBS cables, model coils status and application prospects on future high-energy accelerators will be presented.
With the substantial development underway to seek alternatives to diesel and gasoline driven propulsion for various forms of transportation, cryogenic-based platforms are receiving renewed interest for aviation, space, trucking, marine, and railway. A big reason for this is the presence of a cryogen as a fuel source that can be utilized to achieve greater electrical efficiencies in the respective drivetrains. Noteworthy elements of the drivetrain are the motors and the cabling in which superconductivity can be achieved. This talk will focus on the power electronic technologies and the circuit topologies built from those components that can thrive in these cryogenic conditions. Design guidelines will also be provided to ensure that the resulting system is reliable as not all components have sufficient performance to be included in the cryogenic domain and must remain at higher temperatures.
Highly efficient electrically driven avionics have led to a renewed interest in cryogenic propulsion systems with the goal of reducing carbon emission footprint. Although cryogenic converters promise better efficiency and improved power density, successful design is incumbent upon the appropriate switching device selection and simulation-based analyses prior to initial prototyping. In addition to having components, such as power semiconductor devices, suitably packaged to be able to thrive at cryogenic temperatures and over thermal cycles, it is also important to have compact models for these components to analyze circuit topologies prior to prototype and manufacturing. Elsewhere in the conference, a datasheet-driven compact model for a gallium nitride (GaN) Gate Injection Transistor (GIT) implemented in LTSpice has been presented. Key attributes of this model along with a summary of results indicating why this GaN technology is superior for cryogenic applications is described. This description is a broad summary of the extensive component testing, evaluations, and modeling that the UA team has performed over the past 4 years.
In the last portion of the talk, the circuit topologies and design techniques will be described. A baseline case of a non-cryogenic power electronic motor drive will be described initially. This 250 kW and 30 kW/kg drive is the result of a design of a hybrid electric aircraft (Cessna 337) that has recently been demonstrated in flight via the ARPAe-owned and Ampaire-operated flying testbed. As a non-cryogenic application, it forms a frame of reference to appreciate gains available when cryogenic solutions are possible.
Overall system performance can be further improved if the power electronic converters can also work under cryogenic temperatures. The gallium nitride (GaN) high electron mobility transistor (HEMT), which has the best overall performance under cryogenic temperatures among various types of semiconductors, has been adopted to design power converter topologies for various applications within the aircraft. GaN devices do not exhibit carrier freeze-out effects in the way that doped semiconductor devices do. However, due to the current limitation of an individual GaN HEMT, power modules with paralleled GaN HEMTs in each switching position are designed. Physical design is extremely important to ensure that electrical parasitics are balanced, thus achieving equal current sharing among paralleled components that in turn leads to longer lifetime. Based on converter power loss and size models, an optimization-based design method is illustrated for select circuit topologies. The theoretical efficiency performance under different operating conditions is presented. The double-pulse test (DPT) is performed to validate the function of a designed half-bridge power module. The thermal test of the power module is conducted to validate the symmetric layout design for the paralleled devices.
GaN HEMT-based power converters with different power levels (from several Watts to several kiloWatts) are evaluated at cryogenic temperature. Due to the degraded performance of conventional magnetic components, air core magnetics are used in these power converters to improve the converter efficiency. Efficiency improvements at cryogenic temperature are observed for all the GaN HEMTs and air core magnetics-based power converters, which are promising for cryogenic power electronics applications.
The increasing electric power demand for future all-electric transportation platforms poses strong challenges to the power distribution architecture for these mobile power platforms. Compared to ambient temperature power conversion architectures, cryogenic superconducting power conversion (< 123 K) does not require higher power distribution voltage with larger conductors and is expected to have higher power conversion efficiency. Different components, including passive and active power devices and associate components (gate driver, isolation component, controller, etc.,), have different characteristics at cryogenic temperatures and thus bring different design considerations and trade-offs for converter topology selection, design optimization, control strategy, and protection designs. While silicon power devices have been demonstrated in cryo-power converters in literature, the emergence of Wide Bandgap (WBG) power devices provides more variables to this cryogenic power conversion design with potential advantages and new challenges.
This paper provides an overview of the advances in cryogenic power converter design and its application, from its component selection and characterization at low temperatures to the converter topology design, comparison, and optimization [1]. The paper uses a cryo-cooled converter example from the author’s lab to explain the WBG power device influences in topology selection, overall architecture design, critical auxiliary circuitry design, and important considerations in low-temperature power conversion experiments and measurements [2,3]. The last part of the paper gives a discussion of envisioned applications, challenges, and potential solutions for future superconducting power conversion systems.
Hybrid power generation and distributed propulsion power have been identified as candidate transformative aircraft configurations for future commercial transport vehicles with reduced fuel burn and harmful emissions. High power converters will be a key enabler for future electrified aircraft propulsion as envisioned by NASA and Boeing [1]. At the system level in aircraft applications, superconducting technologies such as motors/generators along with their supportive power systems will grow in importance. Integrating the associated power electronics into the superconductive motor/generator systems can avoid extra thermal insulation and temperature regulation system, and reduce system complexity and improve the power density.
Cryogenic power electronics offer several game-changing benefits, including 1) improved performance of power semiconductor devices, such as silicon metal oxide field effect transistors (Si- MOSFET) and gallium nitride high electron mobility transistors (GaN HEMT), offering significantly decreased specific on-state resistance and increased switching speed; 2) faster switching frequency operation at cryogenic temperature, greatly reducing the need for passive (e.g. EMI filtering); thereby reducing otherwise bulky filter weight and size; 3) less cooling requirement at extremely low ambient temperatures, and 4) light and/or efficient busbar/connector designs due to the low resistivity of conductors at cryogenic temperature.
This presentation will provide several key perspectives for the cryogenic power electronics design from the component up to the converter level, with emphasis on future electrified aircraft propulsion applications. First, the characteristics of critical components, including power semiconductors and magnetics, at cryogenic temperature are introduced. Second, special considerations, trade, and design studies of cryogenic power converters and filter are discussed. Then, three examples of cryogenically cooled power electronics, including a 40 kW Si-based inverter, a 1 MW SiC-based inverter, and a 1 MVA GaN-based solid-state circuit breaker, will be illustrated. The cooling design, safety considerations, and the protection scheme will be highlighted.
High Temperature Superconducting (HTS) cable systems are being developed for future electric ships and aircraft to support the power distribution networks capable of multi kA ampacities. HTS devices offer a high power density solution for high ampacity cables. There is increased interest in superconducting technologies because of the cryogenic cooling power of liquid hydrogen to be used as fuel for electric generators and/or fuel cells. Notional power systems consisting of HTS power devices are being developed for electric ships and aircraft. The expected power levels of electric ships and aircraft are in the ranges of 20-50 MW and 80-100 MW, respectively. Power system designs need the stability, resiliency, and redundancy of the system in the event of a fault. A failure of a component or a section of the power system should not lead to the loss of power for the vehicle. We have initiated a study to understand the electrical fault propagation in HTS cables carrying 5-10 kA current and the effects of a fault resulting in an arc. One scenario investigated is a parallel electrical fault between the HTS conductor and the inner wall of the cable cryostat at ground potential. The plasma of the arc during a parallel fault will introduce a significant heat load in the cryogenic envelope causing a thermal runaway. The occurrence of the plasma arc may also result in damage to the HTS cable cryostat which could cause a vacuum breach also leading to a thermal runaway. The high ampacity of normal operation means that the fault currents will be even higher. In our investigations, a simplified physical model of the HTS cable with polypropylene laminated paper (PPLP) as electrical insulation was designed and fabricated. A high-current unit with a current capacity of up to 100 kA was used to generate high fault current levels on the model HTS power cables. The fault currents are sustained for periods equivalent to the time required for a protection system to identify and mitigate the occurrence of a parallel fault in the power system. Measurements were performed at up to 10 kA at a voltage level of 1 kV with a capacitance of 330 mF. A high-speed camera was used to film the arc events for visual evaluation of the initiation and propagation of the fault. These measurements were performed at room temperature and 77 K in a liquid nitrogen bath. The data generated in the measurements are used to estimate the energy required to pierce the inner wall of the cryostat that would lead to a vacuum breach. The paper discusses the experimental details, the data generated, and a set of recommendations on the limits of operating and fault currents of HTS cables in the power systems of the electric transport platforms.
This abstract presents a cryogenically-cooled power device packaging in high-altitude applications. The target applications are a more electric aircrafts (MEA) and all/hybrid electric propulsion systems. Typically, higher converter power densities can be achieved over silicon-based devices and GaN HEMT under a cryogenically cooled system, due to a lower on resistance. However, thermal management, size, weight and packaging are still major issues in power stage design. A reduction in converter size and weight are limited by conventional heatsink construction and device attachment methods. Attaching surface-mount (SMT) devices on a conventional fiberglass (FR4) printed circuit boards (PCBs) presents a third packaging issue of thermal management. In order to overcome the problem, many cooling packaging methods have been investigated including heat pipe, liquid cooling, a metal core PCB (MCPCB) and so on. However, these methods have still problems that is how to integrate with proper cryogenic cooling. Thus, it is necessary to secure more heterogenous integration (HI) approaches. In this approach, a power packaging density can be improved at least over 10 times and a cryogenic cooling can be concentrated at the power device. However, there is a lot of technical gaps in terms of a fabrication process and methods as follows: (1) 3DHI packaging for a cryo-cooling (Cross-die connectivity, 3D integration of non-silicon technologies, multi-chip assemblies, heterogeneous interconnect yield, reliability and mechanical stress, multi-layer laser via drilling, cryogenics material selection) and (2) 3DHI Cryo-cooling packaging under a high-altitude (flow rate along the cable with altitude variation, MEMS process for u-cooling channel, heat spread, pressure, leaking and sealing for u-cooling channel and CTE mismatches at extreme high/low temperature). In this abstract, we have investigated a 3DHI-based cooling packaging with a cryogenics temperature. In the final manuscript, a comparative analysis will be provided with regards to a high-power density/packaging.
Clad bimetal conductors combine two diverse metals or alloys that are metallurgically bonded to achieve functional advantages that cannot be obtained with a single metal. The selection of metals or alloys to use is determined by end-use requirements such as electrical, mechanical, and chemical properties. Common clad materials consist of a core, such as aluminum, nickel, steel, or copper alloys, along with a clad layer of silver, gold, copper, or titanium. Applications of these clad material combinations include high-frequency electrical coils, electrical switches, immersion heaters, processing vessels, and material-handling equipment. In this research, we present and explore more unconventional combinations to study and assess novel lightweight clad bimetal conductors (LCBC).
Emerging electrical aircraft topologies that generate thrust by the combustion of liquid hydrogen require electrical components with high efficiency and low masses. The onboard use of cryogenic-cooled lightweight clad bimetal conductors in electric machines or cables represents significant mass reduction and increased gravimetrical power density capabilities. In addition, under cryogenic conditions, these conductors' enhanced current-carrying capabilities enable lower voltage levels. Other applications for LCBC include high-energy physics, superconducting magnets, inductor windings, satellites, and rockets.
The alkali metals sodium, lithium, and potassium exhibit the highest conductivity per unit density of any other metal at room temperature. At 77 K, beryllium and lithium exhibit even higher conductivity per unit density values. These metals present promising lightweight conductor solutions, yet they vigorously react with water (alkali metals) and are toxic (beryllium). These chemical properties hinder the use case of these elements as single metal conductors. On the other hand, containing these metals within an inert clad layer adds functional advantages. For example, copper on lithium creates chemical resistance, promotes electrical conductivity, improves mechanical properties, and facilitates soldering. Other interesting metals included in this study are aluminum, gold, silver, magnesium, and titanium.
This research provides an overview of the properties and applications of lightweight clad bimetal conductors for cryogenic systems. It discusses end-use requirements for onboard electrical aircraft cryogenic applications and compares weight, cost, and performance. It comprehensively studies the core and clad layer material’s chemical, electrical, and mechanical properties by (1) employing the Ashby method to study the conductors' material by systematically relating material performance requirements to quantifiable material properties and (2) a finite element analysis to study lightweight clad bimetal conductors' electrostatic and thermal characteristics. Lastly, careful consideration is given to the manufacturing processes and their challenges, given the properties of the conducting material.