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The Technical Program can be accessed via the Timetable Views on the left.
Any individual presenting at and/or attending the Conference must be a registered participant. Click here for registration information.
The first character of the program number, C or M, represents the Conference designation, C for the CRYOGENIC Engineering Conference (CEC), M for the International Cryogenic MATERIALS Conference (ICMC). The second character, 1, 2, 3 or 4, denotes the day of the Conference: Monday, Tuesday, Wednesday or Thursday. The third and forth characters (Or or Po) indicate whether the presentation is in an oral or poster session. The last character, A-M, differentiates the sessions on a given day.
ALL AUTHORS are requested to electronically publish their Poster and Oral Presentations prior to or during the Conference. Presenters of oral talks must also submit their presentation file to the Speaker Ready Room one (1) day prior to their scheduled presentation.
The Conference Program Book is now available, see left side navigation. The Technical Program detail is current as of June 13. Any changes as of June 13 will be added to an Update Sheet and handed out to Conference Participants at registration check-in.
All other conference information can be found at http://www.cec-icmc.org.
For a list of Exhibitors, please visit: http://www.cec-icmc.org/exhibit/exhibitors/.
For a list of Exhibitors, please visit: http://www.cec-icmc.org/exhibit/exhibitors/.
This presentation discusses the NASA Aeronautics Advanced Air Transport Technology Project’s perspective on electric propulsion technologies for future generations of large transport aircraft. Recent system studies commissioned by NASA and other organizations have identified these technologies as promising approaches to dramatically reduce aircraft fuel consumption, noise, and emissions. These technologies are part of the Project’s overall research portfolio aimed toward developing ultra-efficient commercial aircraft in conjunction with alternative low-carbon propulsion and energy systems to enable safe and sustainable future growth in global aviation. It is anticipated that systems based on both room temperature and cryogenic electrical technologies will be needed in the future. In the near term, room temperature electric systems are likely to impact aviation by making their way onto smaller aircraft and by augmenting traditional propulsion systems on larger aircraft. Cryogenic technologies, including fully superconducting motors and generators in a superconducting and cryogenic electric grid, cryogenic inverters, low-AC-loss superconductors and lightweight cryocoolers, will likely be needed in the far term to deliver the several tens of megawatts of propulsive power needed for large transport aircraft. The presentation outlines the opportunities and challenges for electric, hybrid-electric, and related distributed propulsion technologies for commercial aviation, and describes some of the related concepts and enabling technologies that are currently being developed.
Recovering the acoustic power from the Stirling-type pulse tube cryocooler is of great utility in improving cooling efficiency. In this paper, a two-stage cascade pulse tube cryocooler capable of power recovery is introduced and tested. A displacer, playing a role of phase modification and power transmission, is connected between a primary cooler and a secondary cooler. Experimental investigation was first conducted on the cooling performance of the overall system and the separated coolers. The pressure ratios and pressure waves at two sides of the displacer were then studied. The experimental results showed that displacer not only tuned the pressure wave phase but also amplified the pressure wave amplitude. To better understand the displacer, its mechanical resistance and displacement were further discussed. In addition, the power consumption ratio of the 1st cooler, the 2nd cooler and the displacer were presented. The experimental system achieved a total an exergy efficiency of 37.2 % and total cooling capacity of 371 W at 130 K.
Stirling type pulse tube cryocoolers are very attractive for cooling of diverse application because it has it has several inherent advantages such as no moving part in the cold end, low manufacturing cost and long operation life. To develop the Stirling-type pulse tube cryocooler, we need to design a linear compressor to drive the pulse tube cryocooler. A moving magnet type linear motor of dual piston configuration is designed and fabricated, and this compressor could operated with the electic power of 100 W and the frequency up to 60 Hz. A single stage coaxial type pulse tube cold finger aiming at over 1.5 W at 80K is built and tested with the linear compressor. Experimental investigations have been conducted to evaluate their performance characteristics with respect to several parameters such as the phase shifter, operating pressure and operating frequency of the linear compressor.
Improvement of high temperature superconducting materials lead to a new development of various applications such as superconducting motor, superconducting power transmission cable and superconducting power generator, etc. Those applications require a high capacity and high reliable cooling solution to keep high temperature superconducting materials being around 80K.
In order to meet such requirement, Sumitomo Heavy Industries, Ltd. (SHI) has been developing high cooling capacity single stage pulse tube cryocoolers. In general, pulse tube cryocooler is more reliable than Gifford-McMahon cryocooler or Stirling cryocooler because there are no moving parts at low temperature.
We developed a prototype unit which can provide 364 W cooling power at 80 K and COP is 0.04. The parameters such as the flow smoother length, the regenerator size and the operating frequency, etc., are tested and optimized.
The latest development status and test results will be discussed in this paper.
We report construction of a glass pulse-tube cryocooler with regenerator, pulse-tube, inertance tube and reservoir. The purpose of the device is as a teaching tool, and to generate curiosity. The glass system enables one to observe the inside of the cryocooler while it is operating, create curiosity for first-time observers, and encourage their subsequent questions and investigation. Frost forms on the outside of the cold head of the cryocooler since it is exposed directly to ambient conditions. However, observers cannot see any moving parts or fluid flow because the operating fluid, helium gas, is transparent. The dimensions of the glass regenerator have been determined using Regen 3.3 from given parameters of the conductive porous medium inside of the regenerator and a 150[K] target cooling temperature at the cold head. The geometry of the glass pulse-tube and glass inertance tube have been fixed using an approximate design method, and the entire system parameters checked using SAGE. The thickness of each glass component is based on a charge pressure of around 7[bar] and a pressure ratio of about 1.35. The dimensions of the after-cooler are calculated using ISOHX assuming a gas temperature of 300[K] at the inlet of the regenerator.
A high efficiency single-stage Stirling-type coaxial pulse tube cryocooler (PTC) operating at around 40 K has been developed based on numerical simulation by SAGE software and previous experiment experience. The double-inlet and the inertance tubes together with the gas reservoir were adopted as the phase shifters. Under the conditions of 2.5 MPa charging pressure and 30 Hz frequency, the prototype has achieved a no-load temperature of 23.68 K with 330 W electric input power rejecting at 279 K. It can provide 5 W cooling capacity at 40 K when electric input power increases to 395 W, and 7.56% of Carnot efficiency has been realized. It only takes 11 minutes for the PTC to lower its no-load temperature at the cold end from 295 K to 40 K.
As very low temperature high frequency pulse tube cryocooler has been a hot topic in the field of pulse tube cryocooler, improving the cryocooler’s performance is a common goal of researchers. By integrating the former results, we found that regenerative material is a key factor for the improvement of pulse tube cryocooler’s efficiency. In this paper, some experi-ments were conducted to find the regenerative material which is suitable for 7K, besides this, methods of simulation and experiment were used to investigate the influence of stacking style for performance of 7K high frequency pulse tube cryocooler. Finally, the lowest temperature has dropped from 8.8K to 6.7K and more than 10mW cooling power is able to be provided at 8K with a two-stage thermal-coupled high frequency pulse tube cryocooler used. The results of the cryocooler create a possibility of space application for terahertz detectors.
A recent modification to the cylindrical threaded adjustable inertance tube for pulse tube refrigerators links the two helical flow channels existing between the threads of the inner and outer screws in parallel. The phase shifting performance of an earlier design that was limited by fluid leakage occurring between the channels, is now significantly improved by connecting the two channels in parallel. Measurements of the phase shift angle over the entire operating range of the adjustable device are compared with existing models. The models predict a phase angle shift between pressure and flow waves that range from -65 degrees to +40 degrees with the new parallel flow path configuration. By comparison, the original design could only obtain a phase angle shift between 0 and -30 degrees.
Numerical simulation models for GM type pulse tube cryocooler reported so far require pressure pulse as an input which does not take rotary valve geometry into the consideration and cannot predict the pressure ratio reduction while the cooling down occurs. The unique feature of the proposed model is that instead of fixed pressure waveform as an input to the numerical model, it is capable of calculating the pressure waveform from the flow area variation between stator and rotor of rotary valve. This makes the model capable of numerical simulation of the complete GM type pulse tube cryocooler system including the rotary valve. The present numerical model is based on conservation laws namely mass conservation and energy conservation for gas and solid. The complete model is solved using finite volume method with appropriate boundary conditions. The model is currently applicable to orifice mode of operation and does not take any losses into considerations. The effect of valve timing on cooling performance can be predicted by the model. As the cooling down takes place, the reduction in pressure ratio can be simulated by the model which helps to optimize the system performance by modifying the rotor geometry. The comparison between experimentally recorded waveform and simulated waveform shows the reasonable agreement between them.
Pulse tube cryocoolers are used for cooling applications, where very high reliability is required as in space applications. It is achieved due to the absence of moving parts and lack of contaminations. The Pulse tube cryocooler requires an additional buffer volume depending on the temperature and cooling load. A miniature single stage Inertance Pulse Tube Cryocooler is proposed which operates at 80K to provide a cooling effect of maximum 1W. Coaxial Inertance pulse tube cryocooler with a modified reservoir is suggested, where the reverse fluctuation in compressor case is used instead of a steady pressure in the reservoir to bring about the desired phase shift between the pressure and the mass flow rate in the acceptor (cold tip). Therefore, the large reservoir of the cryocooler could replace the crank volume of the hermetically sealed compressor, and hence the cryocooler is simplified and compact in size. The Modified IPTC can be driven by a Helium compressor with a modified reservoir to become a linear compressor of Stirling-type. The components of the cryocooler consisting of a connecting tube, aftercooler, regenerator, acceptor, flow straightener, pulse tube, warm heat exchanger, inertance tube and the modified reservoir were designed and analysed. The associated losses consisting of the heat conduction through the walls of the regenerator, the pulse-tube, regenerator matrix, and radiation heat losses were taken into account. Each part of the cryocooler was analysed using Sage v11 and Ansys Fluent. The simulation results clearly show that there is about 50% reduction in the reservoir volume for the modified cooler when compared to coolers of its same kind.
LS Cable and System Ltd. (LS C&S) and Korea Electric Power Corporation (KEPCO) performed a project of “Development of Operating and Manufacturing Technology for applying 22.9kV HTS Cable to the Commercial Power Grid” by funding of the Ministry of Knowledge and Economy (MKE) from 2008 to 2013. Through the successful implementation of this project, LS C&S will install the 22.9 kV HTS cable system in Heungdeok-Shingal substations, Korea for the commercialization by early of next year for the first time in the world.
For the cooling system of this project, turbo brayton refrigerator and decompression system are adopted as a main system and back-up one respectively. These equipments has been manufacturing and testing of the performance at the factory. LS C&S will install this cryogenic cooling system in Heungdeok substation by this October. The detailed specifications of the cryogenic cooling system for this project are described in this paper
A cryogenic cooling system is designed for three-phase 23 kV 1.2 kA superconducting fault current limiters (SFCL) under development as part of the KEPCO New Energy Technology Program. The goal of this design is a compact, efficient, and reliable system applicable to a commercial product, based upon our successful operation of distribution level SFCL’s. The HTS components are immersed in three separate liquid-nitrogen cryostats and continuously refrigerated by two GM cryocoolers. In order to achieve the spatial uniformity in temperature and pressure around at 78 K and 0.3 MPa, three cryostats are connected each other by the tubes through which liquid or vapor nitrogen can flow. One GM cooler is located at the top of the cryostats for vapor cooling, and the other GM cooler is placed between three cryostats at the vertical height of liquid level for liquid cooling. The uniqueness of this design is to make an effective thermal connection between three cryostats for simultaneous cooling, as called an integrated cooling system. Three pairs of current leads and bushings are also designed, and the full details of thermal load calculation are presented for immediate manufacturing.
Since the discovery of High Tc Superconductivity in 1986, the technology of High Tc Superconducting (HTS) power cables is getting developed all over the world in a continuous manner for efficient transfer of electrical energy in power transmission. In view of the benefits that can be obtained from usage of HTS cables in future power transmission systems, Applied Superconductivity Laboratory, IIT Kharagpur, in collaboration with Central Power Research Institute (CPRI), Bangalore has developed a 1m. long lab-scale superconducting cable carrying 1 kA current at low voltages (~10 volts). Further, for testing the HTS cable under cryogenic conditions, a flexible co-axial cryostat made out of double walled SS bellows with multi-layer insulation, vacuum in the space between the walls and suitable end-connectors is fabricated. The Superconducting cable assembly containing HTS layer (2G YBCO HTS tapes wound helically around a copper former), PPLP dielectric and insulating layers cooled by liquid nitrogen is tested for superconductivity in the double walled flexible cryostat using an AC power supply (0-1500 Amps AC) and necessary measuring instruments (nano voltmeter, temperature controller). In the present paper, the Voltage – Current characteristic of the HTS cable along with its detailed development procedure is presented.
Great achievements have been made in recent years on the development and manufacturing of high temperature superconductors (HTS) and its application to power system. A series of HTS power devices, including HTS power cable, HTS fault current limiter, HTS magnetic energy storage system, HTS transformer, and HTS motor, have been developed and demonstrated in grid. Different kind of HTS power devices may have different requirements for their cryogenic system, which is composed of a cryogenic container and refrigeration system. This report will focus on the R&D progress of the above-mentioned HTS power devices and its cryogenic systems, and look forward to the future development trend of the HTS power devices.
Cryogenic gaseous helium circulation has been demonstrated as a viable option for some high temperature superconducting (HTS) power system applications, particularly when lower operating temperatures (T < 65 K) are needed to achieve very high power densities. The feasibility of a superconducting integrated power system (SIPS) will depend on the development of necessary technologies that support power distribution such as high power terminations, circuit breakers, cryocoolers, and improved thermal insulation. Potential cryocooler failures and fault currents could lead to excessive heat loads at the cable terminations that need to be mitigated to maintain operability of the cable while contingency plans are activated. Gaseous helium cooled systems are particularly vulnerable for unexpected heat loads due to the low volumetric heat capacity. This study explores the possibility of designing the terminations with sufficient cryogenic thermal storage to mitigate unexpected heat loads. Incorporation of solid nitrogen storage anchored to the copper terminals of superconducting cables in the terminations is being studied as a solution. The thermal storage would maintain the operations of the cable for 5-10 minutes after a system contingency. The latent heat of the stored solid nitrogen and the heat capacities of both the solid and liquid phases are utilized for the required thermal storage. A self-contained system of thermal storage that utilizes activated charcoal in the external buffer to store nitrogen gas that condenses and solidifies during the normal operating conditions and evaporates during a heat surge is being studied as an option. This paper will present the results of cryogenic thermal modelling efforts using finite element analysis techniques. Experimental results on a model thermal storage system are used to validate the modelling results. The benefits of such cryogenic thermal storage on GHe cooled high temperature superconducting power distribution network for SIPS will be presented.
This paper presents the design and preliminary test results of a novel cryogenic mixing pump based on the magnetocaloric effect. The mixing pump is developed to enable long-term cryogenic propellant storage in space by preventing thermal stratification of cryogens in storage tanks. The mixing pump uses an innovative thermodynamic process to generate a fluid jet to promote fluid mixing, eliminating the need for a mechanical pump. Its innovative mechanism uses a solid magnetocaloric material to alternately vaporize and condense the cryogen in the pumping chamber, and thus control the volume of the fluid inside the pumping chamber to produce pumping action. The pump is capable of self-priming and can generate a high pressure rise. This paper discusses the operating mechanism and design considerations of the pump, introduces the configuration of a brass-board cryogenic pump, and presents the preliminary test results of the pump with liquid nitrogen.
The prediction of thermal stratification in a cryogenic propellant tank is necessary for the successful execution of space missions. For the reduction of pressuring gas mass, high temperature gas is used for pressuring which may leads to thermal stratification and hence self-pressurization. The different gravity conditions experienced by the propellant tank affect the thermal stratification. At higher accelerated condition during launch, gravity will be higher and stratification proceeds faster, during orbital insertion gravity will be very low which causes reduction in stratification. The rise in propellant temperature due to stratification leads to cavitation in pump which has to be avoided. So modeling of stratification in cryogenic tank is essential as the liquid propellant must meet the pump inlet condition. A CFD model which can simultaneously account for the heat exchanges within the propellant tank and also heat transferred from ambient during initial active pressurization phase is developed. The amount of ullage gas required, Effect of ullage gas temperature on the development of stratification, variation of pressure inside the tank etc is found out. The results show that, there will be reduction in pressure at the end of active pressurization which is due to phase change and reduction in vapor temperature. A MATLAB code has been developed to investigate thermal stratification during initial active pressurization. It is found that there is fair agreement between the results obtained from the MATLAB code and CFD simulation.
The cooling line for the mechanical cryocooler for the Mid Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST) consists of several meters of small-diameter stainless steel tubing at a normal operating temperature of about 18 Kelvin. Over much of its length this line is surrounded by surfaces at significantly higher temperatures, so it is gold-plated to minimize absorption of thermal radiation. However, the length located inside the blanketed thermal volume containing the JWST science instruments is not gold-plated. Periodic warming of the entire cooling line via cryocooler recycling is required to evaporate water frozen onto the outer surface of the gold-plated tubing. During this process, the line’s temperature will be held for an extended period of time at a temperature as high as 200 Kelvin, and the amount of thermal energy radiated onto surfaces near the instruments is a concern. Thus, it was deemed important to measure the total hemispheric emissivity of the un-plated tubing used in the cooler line as a function of temperature. We describe the measurement technique and present the results.
Although thermodynamic vent system (TVS) has been the promising pressure control technique for the long term on-orbit storage of cryogenic propellant, the current technology readiness level of TVS is still very low, thus it is essential to conduct in-depth research on TVS. In the present study, one experimental rig is built to research the performance of TVS with R123. The tank pressurization, mixing injection and throttling refrigeration phases are separately performed with the external heating power of 795~810W and the initial liquid height of 0.595m. The results show that during the pressurization phase, the tank pressure rise rate is approximately 60.583kPa/h. While the circulation volume flow is 150L/h and the throttling ratio 11.73~13.33%, the throttling refrigeration operates 8 cycle with the total venting gas loss of 20.536kg. The corresponding refrigeration capacity of TVS is in the range of 1127~1362W. Moreover, great fluid thermal stratification forms in the pressurization phase with the maximum temperature gradient appearing in liquid-vapor interface. The liquid thermal stratification is fully developed in the mixing injection phase with 5.48 hours’ consumption for the present experiment. Great refrigeration ability of TVS is showed with the liquid temperature limited in 1.98oC, during the throttling refrigeration phase. Once the operation of TVS finishes, the experimental system is under the free cooling of the external environment air. The effect of injection cold fluid on the vapor temperature distribution has lasted 15min. Then the vapor has a parabolic temperature distribution for lasting about 45min. Under the long time free cooling, a linear vapor temperature distribution is finally formed with the minimum value on the top and the maximum value in the interface. While for the liquid, all test points’ temperature reduce with time. It has saved 41% exhaust loss for 2 hours’ operation of TVS, compared with the direct venting gas approach.
Propellant mass gauging is one of the key technologies required to enable the next step in NASA's space exploration program. At present, there is no reliable method to accurately measure the amount of unsettled liquid propellant in a large-scale propellant tank in micro- or zero gravity. Recently we proposed a new approach to use sound waves to probe the resonance frequencies of the two-phase liquid-gas mixture and take advantage of the mathematical properties of the high frequency spectral asymptotics to determine the volume fraction of the tank filled with liquid. We report the current progress in exploring the feasibility of this approach in the case of large propellant tanks, both experimental and theoretical. Excitation and detection procedures using solenoids for excitation and both hydrophones and accelerometers for detection have been developed. 5% accuracy for mass-gauging was demonstrated for large (100-liter) tanks filled with water for various unsettled configurations, such as tilts and artificial ullages. A new theoretical formula for the counting function associated with axially symmetric modes was derived. Scaling analysis of the approach has been performed to predict an excellent performance for in-space applications and environment.
Filling a vehicular liquid hydrogen fuel tank presents the potential for flammable mixtures due to condensed oxygen from liquid air condensation. Current liquid hydrogen tank designs utilize insulating paradigms such as aerogel/fiberglass materials, vacuum jackets, or inert gas purge systems to keep the outer surface from reaching the condensation temperature of air. This work examines the heat transfer at the refueling connection of the tank to identify potential areas of condensation, as well as the surface temperature gradient. A shrouded inert gas purge was selected to minimize vehicle weight and refueling time. The design of a shrouded inert gas purge system is presented to displace air preventing air condensation. The design investigates 3D printed materials for an inert gas shroud, as well as low-temperature sealing designs. Shroud designs and temperature profiles were measured and tested by running liquid nitrogen through the filling manifold. Materials for the inert gas shroud are discussed and experimental results are presented with suggestions for future design improvement.
Gas bearings are an appealing technology which is widely used in turbo-machine in large cryogenic systems due to its inherent characteristic of oil-free and high-speed capability. The hydrodynamic gas bearings are more effective to cryogenic system but less load capacity and dynamic stability by compared with externally pressurized gas bearings. Etching some grooves on shaft or bearing is proved to be effective by experiments to improve its static and dynamic performance. Due to the hydrodynamic gas bearing performance parameters, such as load capacity and stiffness, are dominated by styles and geometric parameters of groove. In this paper ，the effect of groove styles and geometric parameters to the performance parameters of hydrodynamic gas bearings was presented. And a new style of groove was designed which can effectively improve the static and dynamic performance. we conclude that based on calculation of CFD: geometric parameters of groove do have some influence on static and dynamic of hydrodynamic gas bearings, for each parameter of groove there is a best optimal objective value which makes load capacity and stiffness maximum; The new style of groove presented in this paper has better static performance than spiral style and π-style groove.
The twin screw compressor unit has become more and more popular than other types compressor units in large helium cryogenic system. And the new application with helium as the working medium for the screw compressor unit has some technologies to be refreshed for adapting the large helium cryogenic system. The technologies refer to the rotor profiles, oil-injection parameters, oil separation device and control strategy. The control strategy including control logic, unit warning and unit alarming is introduced in this paper. The strategy was tested with the twin screw compressor test rig. And the results indicated the strategy can be successfully used in the large helium cryogenic system.
The Cold Compressor (CC) is used to lower the saturation temperature of liquid helium (LHe) in varying heat load condition from the application side i.e. Superconducting Magnet and Cryopumps for large tokamak machine. The CC is a key component of typical cold box, attached to the LHe bath, compresses and transfers the vapor generated during the heat exchange via Heat Exchangers as well as the flash generated downstream from the Joule-Thomson (JT) valve connected to the cryoplant.
Emphasis of the present paper is on the conceptual design and performance assessment of the CC. The CC is designed to pump ~0.33 kg/sec of 4.2 K saturated helium vapor at a pressure ratio of ~1.39; with an off-design range of 0.2 to 0.5 kg/sec. Operating speeds are between 10 and 40 krpm, with a speed of ~16 krpm at the design point. Due to different heat loads from superconducting magnets and cryopumps, different process pressure and flow rates of the CC for large tokamak machine are expected. Hence, an important component of CC such as impeller design with blade profile generation has been carried for the higher efficiency of the CC. Characteristics curves of the CC have been obtained at different speed together with system characteristics curve. The study result of the surge and choke conditions of the CC for the stable operation of the system is also presented in the paper. Analysis has been carried out using computational fluid dynamics code to analyze various situations during real operation.
Fusion reactors are generating energy by nuclear fusion between deuterium and tritium. In order to evacuate the high gas throughputs from the plasma exhaust, large pumping speed systems are required. Within the European Fusion Programme, the Karlsruhe Institute of Technology (KIT) has taken the lead to design a three-stage cryogenic pump, featuring an 80 K thermal radiation shield, and two charcoal coated pumping stages; at 15K – 22K for hydrogenic species adsorption and at 5K for helium (a product of the fusion reaction) adsorption. This configuration can provide a separation function of hydrogen isotopes from the remaining gases, thus tritium can be internally recycled and reinjected, limiting its inventory in the machine.
The pumping speed relates directly to the interaction between the gas and the sorbent, characterized by the sticking coefficient which depends on a complex way on the nature of the couple gas-sorbent, the sorbent and gas temperatures, the gas pressure, the specific flow rate to the sorbent surface, and the surface coverage. Since literature related to this topic is scarce and inconsistent, a dedicated experiment was conducted in the large cryogenic vacuum TIMO-2 facility at KIT. A test pump consisting in a charcoal coated panel equipped with electrical heaters for temperature regulation between 5K and 25K, and housed by an 80K thermal shield and inlet baffle, has been tested under various gases, gas mixtures and gas flows with two different geometrical configurations.
The influences of the panel temperature, the specific flow rate to the charcoal surface and the incoming gas temperature on the pumping speed have been characterized. After a description of the experimental set-up, experimental results are discussed and open questions are addressed. In a future work, supporting Monte Carlo simulations should allow for derivation of the sticking coefficient values by comparisons with the experimental results.
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) has built and commissioned an independent Cryogenic Test Facility (CTF) in support of testing in the Radio-frequency Test Facility (RFTF). Superconducting Radio-frequency Cavity (SRF) testing was initially conducted with the CTF cold box at 4.5 K. A Kinney vacuum pump skid consisting of a roots blower with a liquid ring backing pump was recently added to the CTF system to provide testing capabilities at 2 K. System design, pump refurbishment and installation of the Kinney pump will be presented. During the commissioning and initial testing period with the Kinney pump, several barriers to achieve reliable operation were experienced. Details of these lessons learned and improvements to skid operations will be presented. Pump capacity data will also be presented.
Introduction of application and characteristics of active magnetic bearing for helium centrifugal cold compressor is present. With the analysis and simulation of control system, a final solution of the magnetic bearing structure is obtained through entire scheme of AMB design and parameter selection for a cold compressor with helium mass flow 30g/s, which is now being developed at TIPC, CAS. Meanwhile simulation study on electromechanical coupling dynamics of the magnetic bearing rotor system is carried out.
Recently a prototype of 4.5K helium refrigerator with capacity of 250W cooling power is under developing in Technical Institute of Physics and Chemistry (TIPC), CAS China. The helium refrigerator is a modified Claude cycle refrigerator, two helium turbo expanders were dedicatedly designed and fabricated to meet the requirements of Claude cycle helium refrigerator. Reliable static gas bearings are used to support the expander shafts at speed of 230 krpm. During the commissioning, the adiabatic efficiency of two turbo expanders are about 65%, the cooling capacity of the helium refrigerator is 270W.
It is an important factor the resonance between the compressive piston and expansive piston that influence the performance of stirling cooler. Moreover, the seal clearance between the displacer and expansive shell influences the resonance characteristic of displacer. There may be contact and friction between the displacer and expansive shell because of their slight seal clearance. It could influence the dynamic characteristic of displacer and the performance of the cooler. In the paper, the assembling state of displacer and expansive shell was investigated. The impacts of parameters ( for example, the friction coefficient and the quantity of seal clearance ) on the performance of stirling cooler were analyzed. The results can improve the performance, lifetime and reliability of stirling cooler.
The detection of exoplanets is done by measuring very tiny periodical variations of the radial velocity of the parent star. Extremely stable spectrographs are required in order to enhance the wavelength variations of the spectral lines due to Doppler effect. CARMENES is the new high-resolution, high-stability spectrograph built for the 3.5m telescope at the Calar Alto Observatory (CAHA, Almería, Spain) by a consortium formed by German and Spanish institutions. This instrument is composed by two separated spectrographs: VIS channel (550-1050 nm) and NIR channel (950-1700 nm). The NIR-channel spectrograph's has been built under the responsibility of the Instituto de Astrofísica de Andalucía (IAA-CSIC). It has been manufactured, assembled, integrated and verified in the last two years, delivered in fall 2015 and commissioned in December 2015.
Beside the various opto-mechanics challenges, the cooling system was one of the most demanding sub-system of the NIR channel. Due to the highly demanding requirements applicable in terms of stability, this system arises as one of the core systems to provide outstanding stability to the channel at an operating temperature finally fixed at 140K. Really at the edge of the state-of-the-art, the Cooling System is able to provide to the cold mass (~1 Ton) better thermal stability than few hundredths of degree within 24 hours (goal: 0.01K/day).
The present paper describes the main technical approach, which has been taken in order to reach this very ambitious performance. The last section includes the first results measured on the instrument in real operation at the telescope.
OmegaCAM is a wide field camera housing a mosaic of 32 CCD detectors. For the optimal trade-off between dark current, sensitivity, and cosmetics, these detectors need to be operated at a temperature of about 155 K. The detectors mosaic with a total area of 630 cm2 directly facing the Dewar entrance window, is exposed to a considerable radiation heat load. This can only be achieved with a very performing cooling system. In addition this system has to be operated at the moving focal plane of a telescope. The paper describes the cooling system, which is build such that it makes the most efficient use of the cooling power of the liquid nitrogen. This is obtained by forcing the nitrogen through a series of well designed and strategically distributed heat exchangers. Results and performance of the system recorded during the laboratory system testing are reported as well. In addition to the cryogenic performance, the document reports also about the overall performance of the instrument including long term vacuum behavior.
CARMENES is the new high-resolution high-stability spectrograph built for the 3.5m telescope at the Calar Alto Observatory (CAHA, Almería, Spain) by a consortium formed by German and Spanish institutions. This instrument is composed by two separated spectrographs, VIS channel (550-1050 nm) and NIR channel (900-1700 nm). The NIR-channel spectrograph's responsible has been the Instituto de Astrofísica de Andalucía, IAA-CSIC. This was installed at the telescope by the end of 2015, technical commissioning and final tuning of the instrument being extended up to fall 2016.
In that sense, one of the most challenging systems in the instrument involves the Cooling System of the NIR channel. It is a key system within the stability budget and was entirely in charge of the IAA-CSIC. That development has been possible thanks to a very fruitful collaboration with ESO (Jean-Louis Lizon). The present work describes the real performance of the CARMENES-NIR cooling system, mainly focusing on the extremely high thermal stability –in the order of few mK- around the working temperature (138K), as well as the main events and upgrades achieved during commissioning. As a result of such a performance, CARMENES-NIR is a cornerstone within the field of astrophysical instrumentation and, in particular, related to discovery of earth-like exoplanets.
The most sensitive observation mode of the ESO VLT (Very Large Telescope) is the interferometric mode, where the 4 Units Telescope are directed to the same stellar object in order to operate as a gigantic interferometer. The beam is then re-combined in the main interferometry laboratory and fed into the analyzing Instrument. In order not to disturb the performance of the Interferometer, this room is considered as a sanctuary where one enters only in case of extreme need. A simple opening of the door would create air turbulences affecting the stability for hours. Any cold spot in the room might also cause convection which might change the Optical Path by fraction of micron.
Most of the instruments are operating at cryogenic temperatures using passive cooling based on LN2 bath cryostat. For this reason, dedicated strategy has been developed for the transfer of LN2 to the various instruments. The present document describes the various aspects and cares taken in order to guaranty the very high thermal and mechanical environmental stability.
BINP presents the progress in the design of the 2T solenoid for the PANDA detector at FAIR. The paper describes the calculations of mechanical and thermal loads of the changed design of the solenoid.
This cryogenic calorimeter is a cryo-free cryocooler system, focus on investigating beam-based heat load. The experimental results support the R&D of superconducting undulators and superconducting wigglers.
Online experiments at various beam conditions have been started since the cryogenic calorimeter installed in storage ring of Shanghai Synchrotron Radiation Facility (SSRF) at July, 2012. Due to the accomplishment of data acquisition of online experiments, the calorimeter was removed from storage ring at July, 2016.
This paper will describe the following contents:
1) Cryogenic design: some modifications and lessons of cryostat design of this calorimeter will be discussed.
2) Experimental data, analysis and conclusion: curve and result of heat load under various beam conditions will be demonstrated. Also, some suggestions for R&D of cryostat of superconducting undulators and wigglers will be discussed.
The international Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, is a challenging accelerator project for fundamental research in various fields of modern physics. Superconducting dipoles are used to bend the particle beam in the SIS100 heavy-ion synchrotron, the main accelerator of FAIR. The 3 m long curved dipoles of super-ferric design are operated at cryogenic temperatures and allow for fast ramping with 4 T/s. To enable sufficient beam stability in the synchrotron the homogeneity of the magnetic field of $\Delta B/B\leq\pm 6\times 10^{-4}$ is required up to the maximal field of 1.9 T. The design shows an excellent quench behavior and comparatively low AC losses, revealed by an intense measurement program on the first of series (FoS) dipole performed at GSI. However, due to mechanical inaccuracies of the yoke production the FoS magnetic field was slightly distorted. Such corresponding issues were individually proven by advanced magnetic and geometrical measurement systems. Based on a broad survey, a second yoke was produced with significant adjustments of the fabrication process which yielded in a substantially improved mechanical accuracy and, to this end, to a sufficient field quality. Details of the characteristics of the optimized FoS dipole, and the production process with the associated measures of quality control in the series production are presented. First insights in the ongoing series production of the SIS100 dipoles will be given.
Currently there are two 1.1 m long planar superconducting undulators (SCUs) in operation in the Advanced Photon Source storage ring. Their NbTi magnets are cooled with LHe penetrating through a channel in the magnet coil formers. In this scheme, the latent heat of LHe provides an effective energy buffer that allows the magnet to return to normal operation within minutes. An FEA based dynamic thermal model of the SCU is being developed to analyze the behavior of the SCU cryogenic systems during a quench. In this paper, preliminary results of these FEA based calculations and a comparison with current operation of SCUs are presented.
The cooling of the superconducting magnet cold masses with superfluid helium (HeII) is a well-established concept successfully in operation since years in the LHC. Consequently, its application for the cooling of FCC magnets is an obvious option. The 12-kW heat loads distributed over 10-km long sectors not only require an adaption of the magnet bayonet heat exchangers, but also present new challenges to the cryogenic plants, the distribution system and the controls strategy.
The paper recalls the basic LHC cooling concept with superfluid helium and define the main parameters for the adaption to the FCC requirements. Pressure drop and hydrostatic head is developed in the distribution and pumping systems; their impact on the magnet temperature profile and the corresponding cooling efficiency is presented and compared for different distribution and pumping schemes.
The Future Circular Collider (FCC) under study at CERN will produce 50-TeV high-energy proton beams. The high-energy particle beams are bent by 16-T superconducting dipole magnets operating at 1.9 K and distributed over a circumference of 80 km. The circulating beams induce 5 MW of dynamic heat loads by several processes such as synchrotron radiation, resistive dissipation of beam image currents and electron clouds. This beam-induced heat loads will be intercepted by beam screens operating between 40 and 60 K and induce challenging transients during beam injection, energy ramp-up and beam ejection on the distributed beam-screen cooling loops, the sector cryogenic plants and the dedicated circulators.
Based on the current baseline parameters, numerical simulations of the fluid flow in the cryogenic distribution system during a beam operational cycle were performed. The effects of the thermal inertia of the headers on the helium flow temperature at the cryogenic plant inlet as well as the temperature gradient experienced by the beam screens has been assessed. Additionally, it enabled a thorough exergetic analysis of different cryogenic plant configurations and laid the building-block for establishing design specifications of cold or warm circulators.
Both LCLS II 2K cold boxes feature a large vacuum vessel topped by a 2” thick flat plate, buttressed by a central column, that supports six cold compressors and connected piping. Multiple external bayonet arrangements permit modification of the flow path through the box so the nominal flow can be adjusted approximately 24% without altering the internal piping. All piping and the vacuum vessel are designed to meet applicable ASME and ASCE codes for operating, transportation and seismic conditions. AutoPIPE CONNECT was used to perform the piping flexibility analysis and ANSYS 17.2 was used to analyze the vacuum vessel.
Proton Improvement Plant – II (PIP-II) has been planned at Fermilab for providing powerful, high-intensity proton beams to the laboratory’s experiments. The heart of PIP-II is an 800 MeV Superconducting (SC) linear accelerator (Linac), which will provide 1.2 MW proton beam needed for the Long-Baseline Neutrino Facility (LBNF). The SC Linac accelerates the beam from 2.1 MeV to 0.8 GeV and includes five types of SC cavities to cover the entire velocity range required for acceleration of protons. These cavities are Half wave resonator (HWR), Single-spoke resonator (SSR1 and SSR2), Low Beta and High Beta Elliptic 5 – cell cavities (LB650 and HB650) [1]. The PIP-II cryogenic system consists of a Superfluid Helium Cryogenic Plant (SHCP) and the Cryogenic Distribution System (CDS) to the aforementioned SC cavities. The work described in the present article lists out the static and dynamic heat loads for each SC cavity along with the static heat load of the CDS. From the total computed heat load and pressure drop values in the CDS, the basic specifications for the SHCP, required for cooling the SC Linac, have evolved. The mitigation strategies for the heat load along with cryogen delivery to the cryomodules, are discussed in the article. Project specific requirements for the SHCP are also laid out.
Reference:
[1] The PIP-II Conceptual Design Report (Draft), V 1.00, November 29, 2016, available at: http://pxie.fnal.gov/PIP-II_CDR/PIP-II_CDR_v.0._work7.pdf
The Accelerator of CIADS (China Initiative Accelerator Driven System) will be built in the nearly future at IMP in china. All the superconducting cavities will be running at 2K . So a helium cryogenic system has been designed according to the requirements of the CIADS Accelerator. The total heat load of the cryogenic system is about 4.2kW at 2K, 2.1kW at 4.5K and 7.5kW at 60K . And the total 4.5K cooling power is 17.9kW. The paper focuses on the Preliminary design of flow diagram, estimating of heat load.
Requirements for cryogenic system of the CIADS accelerator
The running temperature of cryogenic system for CIADS is 2K, using base-cooled mode. The cooling down time between 300K-100K is required for 2K/h, 100K-4.5K for 5K/h. The running pressure in cryomodule is 30 mbara, the maximum pressure in cryomodule is 3 bar, and the requirement for liquid stability is between ±1%.
The heat load of the cryogenic system
The total heat loads contains heat load of cryomodules, valve boxes, transfer lines, vertical test and horizontal test. The cooling quantity is 4.2kW at 2K, 2.1kW at 4.5K and 7.5kW at 60K. So, the design 4.5K cooling capacity is 17.9kW. And two 10 kW/4.5K equipments is selected for CIADS cryogenic system.
The helium cryogenic system at CHMFL is constructed to supply 4.5K forced flow supercritical helium for the hybrid magnet and produce liquid helium for other cryogenic experimental facilities. An external helium purifier is designed and manufactured to remove contaminants in the helium before fulfilled to the cryogenic system. The helium purifier with operating pressure of 2 MPa is capable of reducing contaminants content in helium from 2% to 5ppm. The purifier contains a dryer, a liquid nitrogen dewar, a tube heat exchanger, cylindrical activated carbon beds submerging in liquid nitrogen bath. Moisture and CO2 are removed by the dryer while O2 and N2 are absorbed by activated carbon. The design principles of the helium purifier contain low cost, low consumption of liquid nitrogen, fast regeneration and easy operation. In this paper, Details of the purifier design is presented, and such technical performance like working capacity, liquid nitrogen consumption, regeneration time and efficiency of the heat exchanger efficiency are tested.
The Spallation Neutron Source (SNS) Central Helium Liquefier (CHL) at Oak Ridge National Laboratory (ORNL) has been without major operations downtime since operations were started back in 2006. This system utilizes a vessel filled with activated carbon as the final major component to remove oil vapor from the compressed helium circuit prior to insertion into the system’s cryogenic cold box. Design calculation showing the expected lifetime of 10 years for this vessel will be presented. The fabrication, installation, and commissioning of a spare carbon vessel will be presented. The plans for connecting the new carbon vessel piping to the existing infrastructure will be discussed.
Large liquid hydrogen (LH2) storage tanks are vital infrastructure for NASA, the DOD, and industrial users. Over time, air may leak into the evacuated, perlite filled annular region of these tanks. Once inside, the extremely low temperatures will cause most of the air to freeze. If a significant mass of air is allowed to accumulate, severe damage can result from nominal draining operations. Collection of liquid air on the outer shell may chill it below its ductility range, resulting in fracture. Testing and analysis to quantify the thermal conductivity of perlite that has nitrogen frozen into its interstitial spaces and to determine the void fraction of frozen nitrogen within a perlite/frozen nitrogen mixture is presented. General equations to evaluate methods for removing frozen air, while avoiding fracture, are developed. A hypothetical leak is imposed on an existing tank geometry and a full analysis of that leak is detailed. This analysis includes a thermal model of the tank and a time-to-failure calculation. Approaches to safely remove the frozen air are analyzed, leading to the conclusion that the optimal approach is to allow the frozen air to melt and to use a water stream to prevent the outer shell from chilling.
Described herein is a comprehensive project—a large-scale test of an integrated refrigeration and storage system called the Ground Operations and Demonstration Unit for Liquid Hydrogen (GODU LH2), sponsored by the Advanced Exploration Systems Program and constructed at Kennedy Space Center. A commercial cryogenic refrigerator was interfaced with a 125,000 liter liquid hydrogen tank and auxiliary systems in a manner that enabled control of the state of the propellant by extracting heat via a closed loop Brayton cycle refrigerator coupled to a novel internal heat exchanger. Three primary objectives were demonstrating zero loss off storage and transfer, gaseous liquefaction, and propellant densification. Testing was performed at three different liquid hydrogen fill-levels. Data was collected on tank pressure, internal tank temperature profiles, mass flow in and out of the system, and refrigeration system performance. All test objectives were successfully achieved during approximately two years of testing. Detailed results are presented in this paper.
A project to import a large amount of liquid hydrogen (LH2) from Australia by a cargo carrier, which is equipped with two 1250 m3 tank, is proceeded in Japan. It is important to understand sloshing and boil-off characteristics inside the LH2 tank during marine transportation. However, the LH2 sloshing and boil-off characteristics on the sea has not yet been clarified. First experiment on the LH2 transportation of 20 liter vessel with superconducting MgB2 level sensors by the training ship “Fukaemaru”, which has 50 m long and 449 ton gross weight, was carried out successfully inside Osaka bay on February 2, 2017. In the experiment, synchronous measurements of liquid level, temperature, pressure and acceleration, also navigation and sea weather data were done. Experimental results of the LH2 sloshing and boil-off characteristics on the sea are discussed in comparison with those under static conditions.
This work was supported in part by a Grant-in Aid for Scientific Research, JSPS KAKENHI Grant Number 24246143, Japan.
The European Spallation Source in Lund, Sweden, is going to be a neutron scattering research center that aims to provide around 30 times brighter neutron beams than any other existing facility. As one subsystem of the target station the Cryogenic Moderator System (CMS) slows down high energy neutrons from the spallation process. To gain maximum neutron flux intensities along with high system availability for condensed and soft matter research, an optimized liquid hydrogen moderator circuit has been developed. Hydrogen with a pressure below critical, a temperature around 17 K, and a parahydrogen fraction of more than 0.995 will be utilized to interact with neutrons in a unique moderator vessel arrangement. A helium refrigerator, the Target Moderator Cryoplant (TMCP), continuously recools the hydrogen mass flow. The pressure stabilization is achieved by a cold buffer vessel in a side stream and different cooling demands are met by a controlled helium bypass around the main hydrogen-to-helium heat exchanger. The safety philosophy, interaction of components, and plans on how to validate functionality prior to hydrogen operation are described in detail.
For Electric Aircrafts of passenger capacity of about 20 and above, there is a clear need to have a high power weight density drive train and energy conversion concept. Conventional concepts (often referred to as “non-cryogenic concepts” are clearly limited in this figure of merit [1] to about 20 kW/kg (for MW size motors). The use of cryogenic machines or superconducting concepts might double this figure.
In addition, high efficiency is a crucial aspect of rotating machineries in propulsion (for ships and aircrafts), and we will elaborate on how HTS technology is breaking some paradigms of conventional electro engineering [2,3,4,5,6].
In addition, changing from big fossil-driven turbines located on wings to electric propulsion motors will offer some additional aerodynamic benefits and might change future aircraft design considerably [1,3].
We will focus on and discuss the state of the art of selected existing HTS machines, the critical design path and components and some functional correlations.
We will highlight foreseeable progress and impact on performance and elaborate on aspects in integration and missing links/ white spots.
Finally we will point out the future prospects and developments which can be expected.
[1] Madavan, N. – “Hybrid-electric and distributed propulsion technologies for large commercial air transports – A NASA perspective”, IEEE energy conversion congress & exposition, Montreal, Canada, Sept.20-24, 2015
[2] Luongo et al. – “Next generation more-electric aircraft: a potential application for HTS superconductors”, IEEE Trans.Appl.Supercond. 19(2009)1055
[3] Masson et al. – “HTS machines as enabling technology for all-electric airborne vehicles”, Superconducting Science and Technology 20(2007)748
[4] de Almeida et al. – “Standards for efficiency of electric motors” IEEE Industry Applications Magazine Jan/Feb.2011
[5] DOE EERE call for next generation rotating machines: enabling technologies, DE-FOA-0001467, 09.Mar.2016
[6] Arndt,T. – “Superconductivity for Electric Aircraft”, talk on workshop on “Regional Electrical Aircraft”, 29th June to 1st July 2015, Airbus Defence and Space, Munich/Unterschleißheim, Airbus Group & European Council of Academies of Applied Sciences, Technologies and Engineering (Euro-CASE)
[7] IEEE roadmap on next generation of large electric machines (sponsored by Grainger CEME, NASA and IEEE) – in preparation
Megawatt (MW) class electric power systems will be needed in the next 5-10 year timeframe, not only for directed energy (DE) applications, but also for hybrid-electric or electric propulsion drivetrains for aerospace vehicles. There is question whether conventional technologies already established can meet this challenge with sufficient power densities and efficiencies, or whether alternate technologies might be needed such as cryogenic and/or superconducting. It is already established that Cu-wire technologies, as heavy as steel, are simply too heavy for some aerospace applications Superconducting/cryogenic power system components have intrinsic advantages for MW power systems, such as greatly size, weight and power (SWaP) requirements. In this paper, these unique properties and technical readiness assessment of different cryogenic and superconducting components will be reviewed, and compared to alternate traditional technologies such as Cu-wire based and semiconducting. The impact of these technologies will also be provided, for case-studies of hybrid-electric aircraft.
Hybrid electric propulsion aircraft are proposed to improve overall aircraft efficiency, enabling future rising demands for air travel to be met. The development of appropriate electrical power systems to provide thrust for the aircraft is a significant challenge due to the much higher required power generation capacity levels and complexity of the aero-electrical power systems (AEPS). The efficiency and weight of the AEPS is critical to ensure that the benefits of hybrid propulsion are not mitigated by the electrical power train. Hence it is proposed that for larger aircraft (300 pax) superconducting power systems are used to meet target power densities.
Central to the design of the hybrid propulsion AEPS is a robust and reliable electrical protection and fault management system. It is known from previous studies that the choice of protection system may have a significant impact on the overall efficiency of the AEPS [1]. Hence an informed design process which considers the key trades between choice of cable and protection requirements is needed. To date the fault response of a voltage source converter interfaced DC link rail to rail fault in a superconducting power system has only been investigated using simulation models validated by theoretical values from the literature.
This paper will present the experimentally obtained fault response for a variety of different layups of YBCO superconducting tape for a rail to rail DC fault. The paper will then use these as a platform to identify key trades between protection requirements, and cable design, providing guidelines to enable future informed decisions to optimise hybrid propulsion electrical power system and protection design.
1. C.E. Jones, P. J. Norman, S. J. Galloway, M. J. Armstrong, A.M. Bollman, “Comparison of candidate architectures for future distributed propulsion aircraft”, IEEE Transactions on Applied Superconductivity, Vol.26, Issue 6, 2016.
A cryo-magnet system has been constructed using a single grain GdBa2Cu3O7-δ (GdBaCuO) bulk superconductor of diameter 30 mm. The bulk superconductor was cooled by conductive cooling, employing a portable Stirling cryo-cooler with a base temperature of 51 K. The superconducting cryo-magnet can be repeatedly charged by a pulsed field magnetization (PFM) system that is considerably compact.
A flux jump behaviour was observed consistently during magnetization when the applied pulsed field, Ba, exceeded a critical value (e.g. 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in our practical quasi-permanent magnet system.
A trapped field of over 1 T at 5 K and 0.5 T at 20 K has been measured between a stack of magnetized cylinders of bulk polycrystalline Ba0.6K0.4Fe2As2 superconductors 10 mm in diameter and 18 mm in combined thickness. The trapped field showed a low magnetic creep rate (~3% after 24 hours at 5 K), while magneto-optical imaging revealed a trapped field distribution corresponding to uniform macroscopic current loops circulating through the sample. The superconductors were manufactured by hot isostatic pressing of pre-reacted powders using the scalable powder-in-tube technique. A high Vickers hardness of ~3.5 GPa and a reasonable fracture toughness of ~2.35 MPa m0.5 were measured. Given the untextured polycrystalline nature of the cylinders and their large irreversibility field (> 90 T), it is expected that larger bulks could trap fields in excess of 10 T.
1) J. Weiss, A. Yamamoto, A. Polyanskii, R. Richardson, D. Larbalestier, E. Hellstrom, Supercond. Sci. Technol. 28, 112001 1-6 (2015).
We would like to thank W. Starch and B. Hainsey for technical. The work at ASC was supported by NSF (No. DMR-1306785) and the facilities of NHMFL are supported by State of Florida and by NSF through a facility grant (No. DMR-1157490). The work at TUAT was supported by JST-PRESTO, JSPS and MEXT Elements Strategy Initiative to Form Core Research Center.
A classical method used for determining $J_c$, the critical current density in superconducting cylinders consists in measuring the magnetic field along the superconductor axis after field cooling the sample. Supposing that the current generating the trapped field flows in the whole sample, the trapped field is proportional to $J_c$ and the obtained curve can be reproduced with the Chen et al. expression [Chen et al. Journal of Applied Physics 72, 1013 (1992)], using $J_c$ as a fitting parameter. However, confirming some numerical simulations, a combination of trapped field and levitation force measurements carried out at 77K has shown that the current flows in a restricted region of the cylinder with thickness t, that does not depend on the magnetization process of the superconductor [P.Bernstein et al. Supercond. Sci. Technol 29 075007 (2016)]. Here, we report levitation force and trapped field measurements carried out on both a $MgB_2$ and a $YBa_2Cu_3O_7$ cylinder in a large temperature range in order to investigate the dependence of t on temperature. The results show that t decreases as the temperature decreases. A consequence is that the trapped field can no longer be considered as proportional to $J_c$. This behaviour is due to the magnetic energy stored in the superconductor, that does not depend on its temperature. As a result, t behaves as $J_c^{-2/3}$, while the trapped field along the axis of the cylinder behaves as $J_c^{1/3}$ . These claims are substantiated by the experimental results obtained with both samples.
Large, single grain bulk (RE)BaCuO [(RE)BCO] superconductors have potential to generate magnetic fields that are much greater higher than those produced by conventional permanent magnets. The top seeded melt growth (TSMG) technique has been developed over the last 25 years to fabricate large, [(RE)BCO single grain samples that eliminate current limiting grain boundaries in the bulk microstructure. Although successful, there are a number of problems associated with the nature of the TSMG technique, including porosity, sample shrinkage and inhomogeneity in the distribution RE-211 content throughout the volume of sample, which leads to inefficient flux pinning. As a result, a new process based on top seeded infiltration and growth (TSIG) has been developed relatively recently as an alternative approach for the fabrication of large (RE)BCO single grains. The TSIG technique yields samples that are more dense, more uniform and have potentially better properties than those produced by TSMG. However, it is considerably more challenging to fabricate large-sized samples by this technique due to the relative complexity of the process. We describe the TSIG process and its application to a variety of (RE)BCO bulk superconductors and report the successful fabrication of single grains of up to 37.5 mm in diameter YBCO by a novel, 2-step TSIG process. This process enables a straightforward and very reliable growth process, which has clear practical implications for the manufacture of bulk samples for commercial applications. Details of the development and optimization of the microstructures and the superconducting properties of the (RE)BCO samples fabricated by this novel
technique are presented.
This work deals with bulk, large grain superconductors used as permanent magnet for rotating machines or levitation applications. It has recently been shown that the magnetic properties of bulk large grain superconductors can be improved easily by attaching a short section of a soft ferromagnetic material (F) to one of the faces of the bulk superconductor (S), thereby producing a hybrid F/S structure [1]. Here we investigate the contactless determination of the magnetic behavior of such structures using a recently constructed bespoke magnetometer based on the flux extraction technique [2]. This device allows magnetic moments as large as 1 Am² to be measured at 77 K and accommodates large bulk samples up to 20 mm diameter. This extends significantly the accessible measurement range of “off-the shelf” magnetometers. Unlike techniques based on recording the distribution of flux at the surface of the sample, the measured signal is representative of the superconducting currents flowing across the entire volume of the sample. In the present work we examine the properties of permanently magnetized superconductors and hybrid structures, and measure the irreversible demagnetization of these structures when they are subjected to magnetic field cycles that are not parallel to their magnetization. We also investigate the levitation behavior of hybrid structures subjected to the non-uniform field of a permanent magnet or a combination of permanent magnets used as guideway for levitation applications, and compare the results to those obtained with a bulk superconductor alone.
References:
[1] Egan R. et al., Rev. Sci. Instrum. 86 (2015) 025107
[2] M. P. Philippe et al., Supercond. Sci. Technol. 28 (2015) 095008
Acknowledgments:
We greatly acknowledge Nippon Steel & Sumitomo Metal Corporation for providing bulk large grain GdBa2Cu3O7 (GdBCO) samples.
At the University of Twente, a vibration-free hydrogen-based sorption cooler is under development for cooling optical detectors in future scientific space missions. Depending on the operating pressures in the system, the cooler can be used can be used as stand-alone or as a precooling stage for a helium cooler establishing 4 K. In an earlier ESA project, a hydrogen-based sorption cooler was built and tested of which the compressor cells were at a radiator temperature of 87K. A second small radiator precools the high pressure gas to 51K. The gas is compressed in two stages: from 0.1 bar to 3 bar and from 3 to 50 bar by heating the sorber cells to 200K and 240K, respectively. In this compression phase the cells are isolated from the heat sink by gas-gap heat switches. The cold tip of the JT cold stage reached 14.5K and had a net cooling power of 35 mW. In the present paper we report on an ESA-CTP (Core Technology Programme) project that aims to increase the TRL level of 4 to 5, which is carried out in cooperation with Airbus DS. The redesign of the compressor cell and the check valves will be discussed. The cell and check valves were subjected to relatively high shaker-vibration loads (45 g random). Prior to and after the shaking, the performance of the compressor cell and of the check valves is measured. Test results and further development will be discussed.
As observed in the earlier studies, helium is more efficient than neon as a refrigerant in a reverse Brayton cryocooler (RBC) from the thermodynamic point of view. However, the lower molecular weight of helium leads to higher refrigerant inventory as compared to neon. Thus helium is suitable to realize the high thermodynamic efficiency of RBC whereas neon is suitable for the compactness of the RBC. A binary mixture of helium and neon can be used to achieve high thermodynamic efficiency in the compact reverse Brayton cycle (RBC) based cryocooler. In this paper, an attempt has been made to analyze the thermodynamic performance of the RBC with a binary mixture of helium and neon as the working fluid to provide 1 kW cooling load for HTS power cables working with a temperature range of 50 K to 70 K. The basic RBC is simulated using Aspen HYSYS V8.6®, a commercial process simulator. Sizing of each component based on the optimized process parameter for each refrigerant is performed based on computer code developed using Engineering Equation Solver (EES-V9.1). The recommendation is provided for the optimum mixture composition of the refrigerant based on the trade-off factors like thermodynamic efficiency such as the figure of merit and exergy efficiency, equipment considerations, and inventory management. The outcome of this study may be useful for recommending a suitable refrigerant for the RBC operating at a temperature level of 50 K to 70 K.
The performance of a Joule Thomson (JT) cryocooler can be improved by introducing an ejector into the JT cooling cycle. The function of the ejector is to lift the pressure of the gas leaving the evaporator to a higher level, thus reducing the cold-end temperature and/or the input power of the compressor. In this paper, the performance of an ejector operating with nitrogen gas is investigated experimentally and numerically. The effects of geometry and operating parameters on the ejector performance are analyzed. The validity of the numerical model is verified by comparison between the predicted and measured overall ejector performance. Meanwhile, the local flow features of the ejector are visualized through numerical modelling.
Several precooled JT cryocoolers (JTC) working at 4 K have been developed for space missions. Although these cryocoolers are qualified with high reliability and long life time, their efficiencies are relatively low which is worth further research.
A JT cryocooler has an intrinsic limitation on its cooling power. The intrinsic limitation is that the JTC will be warmed up continuously when the heat load exceeds a certain maximum, which is defined as the maximum specific cooling power (MSCP). The MSCP is equal to the isothermal enthalpy difference at the warm end of the recuperator determined by the high pressure and precooling temperature. The mechanism and the JTC behavior related to the intrinsic limitation will be illustrated with systematic theoretical analysis.
When the MSCP is achieved by a helium-4 JTC, the cooling temperature may be already higher than the critical point. So the maximum specific cooling power at 4 K (MSCP4) should be defined for cooling-performance optimization. The discussion on the MSCP4 explains why the JTC would have optimal high pressures not the same as those give the MSCPs.
Furthermore, the theoretical analysis will be applied to explain a real case based on the acquired experimental data.
Turboexpander is a key focus area for Bhabha Atomic Research Centre (BARC), Mumbai, India in the program for development of helium refrigerators and liquefiers for intra departmental requirements. To start with, a turbine impeller with major diameter 16 mm and design speed of 264,000 RPM, suited for use in the 1st stage of a modified Claude cycle/ reverse Brayton cycle based standard helium liquefier/refrigerator, was developed. The turboexpander rotor was subjected to extensive testing in laboratory followed up with field trials mounted in a helium refrigerator unit developed by BARC. Isentropic efficiency exhibited by the turbine stage was computed to be about 63%. Later on, a second series of turboexpander with the same major diameter (16 mm) and design speed of 260,000 RPM was developed with “splitter” blades at the major diameter end. Yet another turboexpander series, size 16.5 mm and design speed 168,000 RPM, was also developed suited for use in the 2nd stage of a standard helium liquefier/refrigerator. The 1st stage “splitter” bladed turbine along with the 2nd stage turbine units were mounted onto a helium liquefier developed by BARC. During extensive field trials, the helium liquefier exhibited a maximum liquefaction capacity of about 32 l/hr and 195W refrigeration. The 1st and 2nd stage turbine maximum isentropic efficiencies were computed to be in excess of 72% and 67% respectively. High strength aluminium alloy was chosen as the material of construction for the turbine and brake wheel impellers to increase the maximum permissible rotor speed. The present article describes these development efforts at BARC, including results obtained during field trials with the developed helium refrigerator and liquefier.
Strong of 60 years of innovation and design in the field of cryogenic turbomachines, Air Liquide Advanced Technologies is constantly developing new products. Magnetic bearings technology is used since the mid 80’s for specific applications where reliability and efficiency is a key issue. 50 cold compressors, 5 pumps and 5 high power turbomachines (moto-compressors, moto-turbo-compressors and turboalternators) have been delivered in the past years and 29 magnetic bearings turbomachines will be delivered by ALAT in 2017. The first supercritical helium pump of Air Liquide new standard range of cryomachine was commissioned successfully in 2016 for the JT60 project. The compression map of the pump was measured and in very good accordance with the calculations. A new 175kW turbomachine installed on Turbo-Brayton refrigeration system has been commissioned and characterized in 2016. The compression map of the centrifugal compressors and the efficiency of the turbine have been measured. This paper presents the commissioning results of these 2 new turbomachines on magnetic bearings.
Superconducting bearings are used in a number of applications for high speed, low loss suspension. Most of these applications have a warm shaft and require continuous cooling, which leads to additional power consumption.
Therefore, it seems advantageous to use these bearings in systems that are inherently cold. One respective application is a submerged pump for the transfer of liquid helium into mobile dewars. Centrifugal pumps require tight sealing clearances, especially for low viscosity fluids and small sizes. This paper covers the design and qualification of the superconducting YBCO bearings for a laboratory sized liquid helium transfer pump.
Oil contamination is a re-occurring issue in cryogenic helium applications resulting in reduced performance and eventually the need for thorough cleaning of the coldbox internals. Main sources are the oil-injected recycle gas screw compressors. Although the systems are equipped with oil removal systems, mal-operation, improper design, and particularly the carry-over of the residual content of a few ppb will result in accumulation of oil in the coldbox over a longer period of operation. In cooperation with Kaeser, Linde Kryotechnik has modified helium screw compressors for operation with ionic liquids. Ionic liquids exhibit similar tribological properties as for example Breox oil, but are characterized by negligible vapour pressures.
The presentation will show the consequences on liquid carry-over into the coldbox, on equipment sizing of coalescers and adsorbers, as well as on efficiency and power consumption.
The indigenous design and development of helium turbines of 500 W/4.5 K cryogenic system have been started at ASIPP, China. This paper briefly discuses the design process and the fabrication drawings for the whole helium turbine system, which includes the turbine wheel, nozzle, diffuser, shaft, brake compressor, two types of bearing, appropriate housing and some other necessary parts. With the design process, it is possible to design a new turbine for any other fluid cryogenic system , since the fluid properties are properly taken care of in the relevant equations of the design procedure.
Key words：helium turbines，500 W/4.5 K Helium refrigerator, Turbine Design,Testing.
To perform Micro Magnetic Resonance Imaging (μ-MRI) analysis on small regions such as skins, articulations or on small animals, the required spatial resolution imply to dramatically improve the sensitivity of the detection. One way to go is to use miniature radio-frequency superconducting coils that allow, among others, increasing significantly the signal-to-noise ratio. The RF probes, constituted of optimized YBaCuO film coils cooled below nitrogen temperature, must be located no further than few millimeters from the biological region to be imaged in a clinical 1.5 T MRI magnet. To fulfill the medical environment and constraints, a cryogen-free cooling scheme has been imagined to maintain the superconducting coils at the working temperature. The cryogenic design is based on a pulse tube cryocooler and a solid thermal link inserted in a non-magnetic cryostat to avoid creating any electromagnetic perturbations to the MRI magnet. We report here the conceptual design of the cryogenic system with the required thermal performances, the corresponding layout and architecture of the system as well as the main technical challenges which have to be met for the construction.
Over the past decades cryopreservation and cryo-imaging techniques have been intensively developed for structural and functional studies of biological samples at the sub-cellular level. To achieve this, ultra-high resolution imaging techniques such as cryo fluorescence microscopy, cryo electron microscopy, or cryo mass spectrometry are employed. Often these methods make use of commercially available vitrified sample transfer systems. But nearly all these transfer systems are built for a specific cryo-imaging or –analysis instrument and cannot be used for correlation studies. The aim of the present project is to develop a more generally applicable, light-weight system for transferring vitrified samples among imaging modalities, even over significant (i.e. 200 km) distances.
Our cryogenic transfer system consists of three building blocks: a storage chamber, adaptation flanges that allow the connection to different imaging modalities, and a mobile liquid N2 refilling unit. The storage chamber is furthermore equipped with a laser-welded vacuum-isolated low consumption liquid nitrogen cryostat and an innovative thermally shielded cryo-sample stage. This system produces a high vacuum environment, optimized transfer temperature, as well as both horizontal and vertical sample exchange possibilities between high-resolution cryo-imaging instruments. A liquid N2 level monitoring system, powered by a single 3V cell battery, is developed to ensure the cryogenic transfer conditions for vitrified samples over long distances. The complete transfer system has a weight of ~ 5.3 kg and maintains stable cryo-conditions at the sample stage for 2 hours. With the mobile liquid N2 refilling unit, this transportation system can extent stable cryo-conditions that permit transport over long distances of hundreds of kilometers.
In summary, our system allows contamination-free sample transportation between different imaging modalities without active components, e.g. vacuum pumps, cryo-coolers, and other power-requiring systems. Because of its flexible configurability it can come to play a vital role in cryobiology imaging and research.
The temperature distribution of the simulated living tissue is measured for the improvement of the cooling rate during cryopreservation when the surface condition of the test sample is changed. Agar with the 1.5 wt% is used as a simulated living tissue. The test sample is the cylindrical shape and the size is ϕ8.2 x 45 mm. The inside of the test sample is filled with agar. The surface of the test sample is covered with the stainless steel mesh. The variation of the transient temperature with the specification of the mesh by the directly immersion in the liquid nitrogen is measured. The temperatures on the sample surface and the inside of the sample are measured by use of type T thermo couples. It is confirmed that on the sample surface there is the slightly temperature increase than that in the saturated liquid nitrogen at the atmospheric pressure. It is found by the comparison of the degree of superheat with or without the mesh that the surface temperature of the test sample with the mesh is lower than that without the mesh. On the other hand, the time series variations of the inside temperature located in the center of the sample does not change with or without the mesh. It is considered that the center of the sample used in the present study is too deep from the surface to respond to the boiling state on the sample surface.
Interest in low temperature treatment is constantly increasing. Whole-body cryotherapy (WBC) devices are becoming available not only in medical centers but also in local gyms and spa centers. A new group of users are professional sport clubs where 3-minutes session of whole-body cryotherapy is post-training procedure to improve and speed up the recovery process.
Currently, there are four types of WBC devices available on the market and offered to commercial (non-medical) users. European and American market is dominated by two of them: classic cryochambers and cryosaunas, respectively. Both constructions are supplied with liquid nitrogen. Low temperature inside classic cryochamber is produced by evaporating of liquid nitrogen in two or more heat exchangers. There is never a direct contact between user and cryogenic medium in any of system operation mode. Therefore, supply system is categorized as closed one. Cryosauna is cooled down by filling with cold vapor of liquid nitrogen. Supply system is considered open because it allows for direct contact between user and cryogenic gas. Open supply system of cryosauna is primary and most questionable issue of its operational safety, particularly after tragic accident in October 2015.
This paper presents the comparative analysis of classic cryochamber and cryosauna from safety point of view. Both devices have been analyzes and tested on existing systems in operation. Paper gives detailed analysis of constructions, supply systems and working parameters. Special attention has been focused on problem of oxygen deficiency hazard. Different failure or accident scenarios have been analyzed and discussed.
Molecular technologies in cancer diagnosis require fresh and frozen tissue, which is obtained by means of snap-freezing. Currently, coolants such as solid carbon dioxide or liquid nitrogen are used to preserve good morphology of the tissue and to keep the molecular activity intact. Using these coolants, snap freezing of tissues for diagnostic and research purposes is often time consuming, laborious, even hazardous and not user friendly. For that reason snap-freezing is not routinely applied at the location of biopsy acquisition. Furthermore, the influence of optimal cooling rate and cold sink temperature on the viability of cells is not well known. In this paper, a snap-freezing apparatus powered by a small cryocooler, is presented that will allow bio-medical research of tissue freezing methods and is safe to use in a hospital. To benchmark this apparatus, the cool down of an aluminium cryo-vial in liquid nitrogen is measured, which has a cooling rate of -25 K/s. A forced convective helium gas flow through a gap around the cryo-vial obtained sufficient cooling rates and is chosen as the preferred cooling method. A conceptual design of the snap-apparatus with forced flow is discussed.
Cold storage of biological specimens generally falls into two categories: (1) "Ultra-low" mechanical freezers, which are technologically close cousins of domestic vapor-compression freezers, and (2) liquid-cryogen-cooled dewars. The first type are expensive to run, and give off a lot of waste heat which must in turn be removed from a laboratory or work area, and can only reach moderately cold temperatures (-86 C, typically), well above the 'glass transition temperature'. The second type enable very cold storage, and don't consume electricity or waste heat--but they consume sacrificial cryogenic liquid which must continually be replenished. This is not economical or convenient without bulk cryogen storage and permanent VJ piping to automatically refill the freezers, which is not practical for many locations. Recently, Chart Inc. has combined its expertise in storage dewars with its efficient Q-Drive cryocoolers to produce efficient biofreezers that require no sacrificial cryogen. Using a dewar instead of a standard refrigerator box for the storage space reduces the heat leak to only a few watts, which can easily be overcome by a cryocooler mounted on the top of the dewar. The first such product from Chart, the "Fusion" freezer, uses an internal 50-liter cryogen tank to provide both heat exchange surface for cooling the storage space and also 'hold time' in case of a power outage. The cryocooler is mounted directly to this internal tank, and reliquifies the cryogen as it boils off. The 1500-liter storage space is maintained below -160 C for an average power draw of 320 watts. The cost of the system is expected to be comparable to existing -86 C freezers.
Fully superconducting power systems in electric aircraft and all-electric ships will have many power conversion and conditioning stages between the generators, transmission cables, storage devices, and loads such as motors. The system level efficiency suffers from heat leak from ambient if the power has to leave the cryogenic environment of a superconducting device for power conversion and conditioning before entering a second superconducting device. A substantial share of the total heat leak is located at the interfaces between cryogenic devices and room temperature devices. It is, therefore, an important goal to minimize the number of non-cryogenic power devices and cryogenic to normal interfaces.
To increase the system-level efficiency, simpler designs, and to increase reliability, power electronic converters operating at cryogenic temperatures are needed. Besides minimizing the heat loads at the interfaces, cryogenic power electronics can offer other benefits such as higher power density and simpler integration of various devices. However, there are several obstacles to overcome before cryogenic power electronics technology reach maturity. While semiconductors and small power electronic devices have been studied at cryogenic temperatures and certain topologies have been identified as promising candidates for cryogenic power electronics, their packaging, interconnects, dielectric aspects, and cooling protocols are still areas of active and much needed research. The topology of the converter has to take into account the limitations and the efficiencies associated with the individual components at cryogenic temperatures. One example is the matrix converter topology, which does not require a DC link capacitor and therefore limits the risk with respect to the need for large cryogenic capacitors.
This paper presents the opportunities and challenges of cryogenic power electronic systems and the results of our attempts in developing suitable topologies and address system and device level issues related to cryogenic thermal and dielectric aspects.
Advanced superconducting generators, cables and fault current limiters have allowed highly-integrated power distribution systems to become more compact and efficient. For the purpose of constructing parallel, multi-terminal cryogenic power systems, switching devices are required to offer protection and control. However, conventional switchgear which connects superconducting components to ambient temperature may lead to substantial heat leak. This heat leak could be significantly reduced if switchgear is designed to operate at cryogenic temperature. This paper evaluates the three conventional switchgear technologies: oil circuit breakers, SF6 circuit breakers and vacuum interrupters with respect to their potential for cryogenic implementations. Their cryogenic counterparts would require substantial changes in both dielectric media and structural design. Cryogenic liquids such as liquid nitrogen (LN2), liquid methane (LCH4), liquid natural gas (LNG), and liquid hydrogen (LH2) are promising candidate fluids for classical oil circuit breakers. We compare dielectric, thermal, and arc quenching properties of cryogenic liquids with those of oil circuit breakers. Similarly, a number of cryogenic gases are compared with SF6 gas concerning their performances. The challenges for cryogenic vacuum interrupters are material compatibility and fatigue. Besides dielectric media, structural designs of cryogenic circuit breakers also need special modifications to include thermal interface between cryogenic switching chamber and control devices in ambient temperature.
High speed, compact, lightweight and highly efficient motors and generators are needed for applications in power and transport systems. Here we discuss one application in an energy storage system for subway station regenerative braking energy storage. In this application high rotational speed (> 25,000 RPM) and rapid two-way high power transfer (> 500 kW) within a small footprint are key performance requirements
An AC Homopolar synchronous machine is an ideal choice for such applications. These machines employ a conventional high speed AC armature winding but utilise a stationary DC excitation winding on the stator that simplifies a design for high rotational speed. The rotor is also simplified to a ferromagnetic solid rotor, with the speed only constrained by the mechanical stress limit of the rotor material. Homopolar machines have been demonstrated that can deliver electrical frequencies in multiple kHz and rotational speeds past 60,000 RPM, but delivering power levels past 10’s of kW has been challenging at high electrical frequencies due to significant cooling losses for the DC field coils. Modern HTS materials are ideal candidates to provide low-volume, high JE, high field DC coils to meet this challenge; replacing the DC field excitation coil with a suitable superconducting coil will lead to MegaWatt class machines.
We describe the design of a homopolar machine with a high temperature superconducting DC excitation coil, an integrated novel brushless flux pump exciter, and analyse the performance for application as a flywheel energy storage unit. The brushless exciter fundamentally reduces the thermal load upon the cryogenic system by removing the need for thermally inefficient normal-conducting current leads and the impact on cryogenic overhead is discussed.
Recent advances in the Nb technology have resulted in the development of superconducting radio-frequency (SRF) resonant cavities capable of producing accelerating fields up to 50 MV/m and achieving very high quality factors exceeding 1010 @ 1-2 GHz and 2K. At such strong RF fields, the density of screening currents flowing at the inner surface of the Nb cavities approaches the fundamental depairing limit, so any further increase of accelerating gradients requires materials with thermodynamic critical fields and superconducting transition temperatures higher than those of Nb. In this talk I will give an overview of basic physics and materials mechanisms which limit the performance of SRF cavities and discuss new opportunities to increase the accelerating gradients by surface nanostructuring using Nb3Sn, NbN, MgB2 or iron-based superconductors in the form of thin films and multilayers deposited on the inner surface of the Nb cavities.
Several particle accelerators like the LHC at CERN use superconducting cavities to increase the energy of charged particles produced by sputter coating a thin niobium film on a copper substrate. Coating technologies used are diode and DC magnetron sputtering (dcMS). Compared to the bulk niobium technology the performance of such thin film cavities is limited by the field dependent RF residual surface resistance. The current application space is therefore usually at relative low frequency (up to 400 MHz), high temperature (4.2 K) and moderate accelerating gradient (a few MV/m). Several new techniques are currently being developed to overcome this limitation. The HiPIMS technology is very similar to dcMS. Films have been deposited and tested on 1.3 GHz test cavities. Other coating techniques like electron cyclotron resonance (ECR) are not yet developed to be deposited on cavities. Here sample tests can give invaluable information on the RF performance. A suitable device which can measure the surface resistance with unpreceded accuracy is the Quadrupole Resonator from CERN, which has more recently been rebuilt and further developed at HZB. Additionally DC methods can be used to probe the superconducting properties of samples and guide the development of the coating process. Two techniques which have been proven to be very informative for SRF developments are muon spin rotation and point contact tunneling. This article reviews RF and DC methods and results on test cavities and samples for SRF application.
MgB2 thin films grown by hybrid physical-chemical vapor deposition (HPCVD) have been investigated for SRF cavity applications. Clean MgB2 thin films have a low residual resistivity (<0.1 µΩcm) and a high Tc of 40 K, promising a low BCS surface resistance. Its thermodynamic critical field Hc is higher than Nb, potentially leading to a higher maximum accelerating filed. The lower critical field Hc1, which marks the vortex penetration into the superconductor and the vortex motion related dissipation, is lower for MgB2 than Nb, but it can be enhanced by decreasing the film thickness. I will present results on the enhancement of Hc1 in thin MgB2 films and coatings, deposition of MgB2 films on Cu, and the coating of RF cavities by MgB2. These results are encouraging for the application of MgB2 for SRF cavities.
Bulk Niobium (Nb) SRF (superconducting radio frequency) cavities are currently the preferred method for acceleration of charged particles at accelerator facilities around the world. However, bulk Nb cavities suffer from variable RF performance, have high cost and impose material & design restrictions on other components of a particle accelerator. Since SRF phenomena occurs at surfaces within a shallow depth of <1 m, a proposed solution to this problem has been to deposit a superconducting Nb thin film on the interior of a cavity made of a suitable alternative material such as copper or aluminum. While this approach has been attempted in the past using DC magnetron sputtering (DCMS), such cavities have never performed at the bulk Nb level. However, new energetic condensation techniques for film deposition offer the opportunity to create suitably thick Nb films with improved density, microstructure and adhesion compared to traditional DCMS. One such technique that has been developed somewhat recently is High Power Impulse Magnetron Sputtering (HiPIMS). In order to test HiPIMS, a systematic study was performed in which Nb films were deposited on coupon samples in multiple “series” where only one parameter (Ion Fraction, Average Condensation Energy, Temperature, Pressure…etc.) is varied at a time. Subsequently, the sample properties were measured using: XRD, AFM, SEM, EBSD and TEM, and correlations were made between deposition parameters and film properties. Here we present the results from the systematic studies performed and show the evolution of the Nb thin film properties as a function of the deposition parameters used across the HiPIMS regime.
A novel patented electro-chemical technique to produce Nb3Sn thin films was reproduced in US labs. The Nb3Sn phase is obtained in a two-electrode cell, by electrodeposition from aqueous solutions of Sn layers and Cu intermediate layers onto Nb substrates. Current densities are between 20 mA/cm2 and 50 mA/cm2, and bath temperature is between 40C and 50C. Subsequent thermal treatments in inert atmosphere are realized at 700C to obtain the Nb3Sn superconducting phase, which is typically between 5 and 10 m in thickness. Nb3Sn benchmark samples were first produced at ANL. Then the technique was further optimized, and samples were characterized for superconducting properties, including Tc0 by transport and inductive measurements, using the existing FNAL infrastructure. The samples critical temperature Tc0 ranged from 17.0 K and 17.7 K, and the samples upper critical field Bc20 ranged between 22 T and 24 T. Flux pinning models in granular A-15 based on Josephson-coupled arrays and anisotropic flux pinning by grain boundaries predict that the Jc of A-15 superconductors could be largely improved by elongating their grain structure and/or nano-engineering the materials. In a next phase of this work, these thin films will be used to test theoretical predictions, as well as flux pinning properties of additional elements inexpensively and with fast turnaround.
Since the electrochemical deposition method is scalable in size and controllable on curved surfaces, applications to superconducting magnetic shields and SRF are in principle possible. In parallel to sample development and fabrication, some R&D effort was put in the electro-polishing of the samples’ outer surface at JLab for future surface resistance measurements, to test adequacy to SRF applications.
Theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor (SIS) structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities. The technological challenges include realization of high quality superconductors with sharp, clean, transition to high quality dielectric materials and back to superconductor, with careful thickness control of each layer. Choosing NbTiN as the first candidate material, we have developed the tools and techniques that produce such SIS film structures and have begun their characterization. Using DC magnetron sputtering and HiPIMS (high power impulse magnetron sputtering), NbTiN and AlN can be deposited with nominal superconducting and dielectric parameters. Hc1 flux penetration field enhancement is observed for NbTiN layers with a Tc of 16.9 K for a thickness less than 150 nm. The optimization of the thickness of each type of layers to reach optimum SRF performance is underway. This talk describes this work and the rf performance characteristics observed to date.
The low temperature measurement station called CABTR (Centrale d’Acquisition Basses Températures Rapide) is an instrumentation, recently developed by CEA, and dedicated to the cryogenic temperature measurement.
Thanks to its data rate acquisition up to 1 kHz/channel and its lock-in measurement to be lowly sensitive to the industrial harsh environment, the CABTR permits to observe fast temperature transients, such as temperature oscillations due to pulse tube cryo-coolers..
Its bandwidth (max 100Hz) can be reduce to increase the accuracy and the distance between the sensor and the station. As an example, this paper will present 4K measurement results with a 300m long thermometric chain.
We also described all means of communication available to integrate easily the CABTR into your installation equipped for example with PLC. Different housings are available and will be described from 8 channels in lab box type to 40 channels in 19inch rack for cubicle mounting (8U).
CEA/SBT has to deliver 277 flowmeters for the control of the ITER superconducting magnets. Some of the flowmeters will operate at room temperature while the remaining ones will operate at cryogenic temperature (5 bar and 5 K, typically). Within the framework of this contract, CEA/SBT has to measure the flow coefficient of the flowmeters that takes into account the fact that the fluid is not completely incompressible and that the pressure drops are not equal to zero. As the use of supercritical helium involves very high Reynolds number, this coefficient was chosen to be measured in the Helios loop coupled to the 400 W @ 1.8 K refrigerator available at CEA/SBT. Since all the refrigerator cooling capacity is absorbed by the cold circulator while characterizing the largest flowmeters, an optimisation of the loop was required in order not to add any electrical heater even if the operating temperature of the loop has to be higher than the temperature of the helium bath of the refrigerator. This optimization allows the whole cooling capacity to be dedicated to the circulating pump in order to maximize the mass flow rate in the flowmeters. The design of the loop was carried out with an EXCEL model resulting from a thorough work. In a second time, a model made with the Simcryogenics library for MATLAB/Simulink was used. The latter demonstrated a great ability (compared to the model made with EXCEL) to solve the problem and the results obtained were compared with those obtained with the EXCEL model. Finally, the results of these simulation tools were compared to the experimental results.
A new approach for automotive hydrogen storage systems is the so-called cryo-compressed hydrogen storage (CcH2). It has a potential for increased energy densities and thus bigger hydrogen amounts onboard, which is the main attractiveness for car manufacturers such as BMW. This system has further advantages in terms of safety, refueling and cooling potential.
The current filling level measurement by means of pressure and temperature measurement and subsequent density calculation faces challenges especially for precise evaluation of the filling level. A promising alternative is the capacitive gauge. This measuring principle can determine the filling level of the CcH2 tank with significant smaller tolerances. The measuring principle is based on different dielectric constants of gaseous and liquid hydrogen, which is successfully utilized in liquid hydrogen storage systems (LH2).
The present theoretical analysis shows that the dielectric values of CcH2 in the relevant operating range are comparable to LH2, thus achieving similar good accuracy. The present work discusses embodiments and implementations for such a sensor in the CcH2 tank.
A cooling system is developed for femtosecond laser experiment. The system includes a vacuum tank and a cooling chamber. It uses liquid nitrogen and helium as cold source and resistive heater as power source which heats the cooled crystal. With the controlling strategy of PID, it can make the temperature of the cooled crystal changed continuously from 5 to 300K. In this paper, the structure of the whole system is introduced and the numerical simulation of the heat leakage and temperature field is presented. Finally, the experiment and the analysis of the difference between experiment and numerical simulation are given. From 5 to 80K, we use liquid helium as cold source, and the fluctuation of the temperature is lower than±0.5K; from 80 to 300K the liquid nitrogen as cold source and the fluctuation of the temperature is lower than±0.8K. Besides, for this system, a flexible pipeline transporting cryogenic liquid nitrogen and helium is invented. Using this flexible pipeline and a two-dimension move platform which is used for fixing the cooling chamber, the angle of the crystal can be changed more than±30°and the location can be changed more than±10mm.
Flow balancing orifice (FBO) are used in ITER Toroidal Field coil to uniform flow rate of the cooling gas in the side double pancakes which have a different length of the conductor of 99 m and 305 m,respectively.FBO consist of straight parts, elbows which are produced from 316L,tube 21.34 x 2.11 mm and orifices which are machined from the 316L rod. Each of right and left FBO contains 6 orifices, straight FBOs contain 4 and 6 orifices.Before manufacturing of qualification samples,JSC NIIEFA proposed to IO ITER new approach to provide the seamless connection between tube and plate therefore the most critical weld between orifice with 1mm thickness and tube was removed from the final design of FBOs. Since the proposed diameter of orifice is 4.5 mm which is three times less than the minimum requirement of the ISO 5167, therefore has been tasked to define correctness of calculation flow characteristic at room temperature and compare with experimental data. In 2015, the qualification samples of flow balancing orifices were produced and tested. The results of experimental data shown, that the deviation of calculated data less than 7%. Based on this result and other tests IO ITER approved design of FBO,which made it possible to start the serial production.In 2016 JSC “NIIEFA” delivered 50 FBOs to the IO ITER, i.e. 24 left side, 24 right side and 2 straight FBOs.To define the quality of FBOs has been prepared the test facility in NIIEFA.The helium tightness test at 10-9 m3·Pa/s under the pressure up to 3 MPa,the measuring of flow rate at the various pressure drops, the non-destructive tests of orifices and weld seams(ISO 5817,class B).Also other tests such as check dimensions and thermo cycling 300 - 80 - 300 K were carried out for each FBO.
A fundamental problem with high temperature superconductors (HTS) is the high Tc values themselves and the stability that they impart. Low normal propagation velocities and high stability of HTS wires cause localized damage of magnet coils when there is a quench. Protection of HTS magnets for reliable operation has proven to be a challenge, particularly in Rare Earth Barium Copper Oxide (REBCO) superconductor, with the amount of energy that is required to get enough of the current into the metallic stabilizer to properly distribute the magnetic energy and minimize peak hot spot temperatures. A twist of a relatively new technique that relies on AC losses to distribute energy is Frequency Loss Induced Quench (FLIQ). FLIQ like CLIQ, drives an imbalance in the transport current between two or more sections of a magnet. In order to drive this imbalance, FLIQ uses an H-bridge design with IGBTs, whose gates are driven based on the feedback response of the voltage across the bridge. This system optimizes frequency, as current resonates at the frequency of the LC network across the bridge. This paper will discuss the novel circuit design, its working principle, and present representative data obtained on an insulated REBCO insert magnet coil.
40 T hybrid magnet combining a set of resistive magnet with a superconducting outsert, was carried out at High Magnetic Field Laboratory, Chinese Academic of Science (CHMFL). The superconducting magnet is forced flow cooled with supercritical helium at a temperature of 4.5 K and pressure above 5 bar. The cryogenic Distribution Box distribute refrigeration power to the outsert superconducting magnets, and the helium temperature of the cryogenic Distribution Box is measured by cryogenic linear temperature sensor(CLTS).One CLTS nearest from 40T hybrid magnet appeared obvious magnetoresistance when superconducting outsert magnetic field is above 7T, and the magnetoresistance are plus or minus alternately with magnetic field,the largest temperature error is 1K.The magnetoresistance disappeared when superconducting magnetic field is below 7T.
This papers deals with the Japan Torus-60 Super Advanced fusion experiment JT-60SA cryogenic system. It follows the results exposed in [1], in which a model of the whole JT-60SA cryogenic system has been presented, and in which PI controllers parameters have been calculated and simulated with a model-based approach. This paper will present the experimental results obtained on the refrigerator during the commissioning phase of the cryoplant. The PI loop that maintain the low pressure stable from the warm compression side has been calculated automatically with a model of the warm compression station and the resulting PI parameters have been applied to the cryogenic system. The same procedure has been applied on the pressure regulation of the supercritical helium loops using a model of the auxiliary distribution cold box. . This paper will prove that it is possible to calculate the PI parameters of the control loops before the machine has been built (with better results than the one that would have been tuned on-line) and thus to save time and reduce cost on utilities (fluids, electricity, etc.) on site, during the commissioning phase. This work is partially supported through the French National Research Agency (ANR), task agreement ANR-13-SEED-0005.
[1] : Modelling and Model-Based-Designed PID Control of the JT-60SA Cryogenic System Using the simCryogenics Library, F. Bonne, P. Bonnay, C. Hoa, G. Mahoudeau, B. Rousset. In proceedings of the 26th International Cryogenic Engineering Conference & International Cryogenic Materials Conference 2016, to be published.
Increasingly, exported forces and torques (EFT) from cryocoolers and other mechanisms are a system level concern with lower levels becoming the norm for instruments with cryocoolers. EFT targets of ≤ 50 mN force and ≤ 25 mN-m torque in the 0-500 Hz range are expected. To meet these targets, Ball Aerospace developed both a low EFT cryocooler mount and a facility in which to make these measurements. This facility and its capabilities will be described herein.
Present cryogenic valves are mostly driven by pneumatic actuators. In general, PLC generated electrical analogue or digital signals are guiding control valves via an electro-pneumatic positioner and digital valves by switching an electromagnetic pneumatic pilot valve. One important advantage of pneumatic actuators is the failsafe function, either closed or open, in case of energy loss. However, the pneumatic air supply system and the electric signal cabling is complicated and the complexity increases with the number of valves. The pneumatic system is energy intensive, needs space and continuous servicing. Therefore operation and capital costs for such an electro-pneumatic system are quite high.
There are new developments in in the refrigeration, natural gas and energy industries which use pneumatic free electric driven control and shut-off valves.
Based on the positive experiences in these industries, innovative cryogenic and warm valves, actuated by an electrical stepper motor were developed. Together with the control module the full functionality including fail open or fail closed positions as well as many further control advantages are available. Using this type of valve allows a highly simplified installation. These advantages open a possibility to reduce operation and capital costs remarkably.
Already available are valves driven by an electrical stepper motor up to size DN40 depending on the requested shut-off pressure. For larger valves and higher shut-off pressures, innovative actuator systems with their own electro-hydraulic drive control system are available.
Examples of such valves will be shown and described. Development perspectives will be discussed.
The JT-60U is being upgraded to a full-superconducting tokamak referred as the JT-60 Super Advanced (JT-60SA) as one of the JA-EU broader approach projects. JT-60SA will use superconducting magnets to confine the plasma and achieve a plasma current with a typical flat top duration of 100 second in purely inductive mode. The JT-60SA refrigerator will provide supercritical helium at 4.4 K for the superconducting toroidal field and poloidal field magnets, 50 K for High Temperature Superconductor Current Leads, 80 K for Thermal Shields, and 3.7 K supercritical helium for the divertor cryopumps. During typical plasma discharge scenarios magnets currents have to be ramped and controlled, helium pressures and flow rates in the cooling loops of the coils and structures have to be adjusted and temperature stability of several components has to be supervised. In abnormal situations the magnet system has to be discharged quickly and brought to a safe condition.
A supervising system called “magnet controller” is being developed to perform the different operation scenarios of the magnet system of JT-60SA.
One of the main control functions of the magnet controller is the smooth cool down of the magnet system. During the cool down, temperature differences between different sections of the magnet system and the structures have to be limited and the cooling requirements have to match the refrigerator´s capacity. Helium flow rates have to be split and distributed to the different JT-60SA loops in proportion to the their masses and specific heat capacities
In case of quench, the magnet controller triggers the ramp-down of the coil current by passing the quench signals from the quench detectors to the Supervisory Control System and Data Acquisition System (SCSDAS) and in parallel to the cryogenic system. In the contribution, the current status of the development of the magnet controller will be presented.
Cryogenic valves built into vacuum isolated coldboxes have to meet high requirements when it comes to tightness to vacuum, tightness to ambient, seat tightness or operational behavior. Since cryogenic tests are cost and time expensive, testing of valves during the manufacturing process is usually done at room temperature. Cryogenic tests however are sometimes necessary due to specific customer requirements or in form of a type test during the development and qualification process. Especially safety relevant cryogenic valves have to reach the highest operating reliability and should thus be tested under conditions as close as possible to the real operating conditions. This poster explains the different tests that were executed during the development, qualification and manufacturing process of cryogenic safety valves. It focuses in detail on the cold tests that were performed on the valves with cryogenic fluids and at cryogenic conditions.
Use of Fiber Bragg Grating (FBG) sensor is very appealing for sensing low temperature and strain in superconducting magnets because of their miniature size and the possibility of accommodating many sensors in a single fiber. The main drawback is their low intrinsic thermal sensitivity at low temperatures below 120 K. Approaching cryogenic temperatures, temperature changes lower than a few degrees Kelvin cannot be resolved, since they do not cause an appreciable shift of the wavelength diffracted by a bare FBG sensor. To improve the thermal sensitivity and thermal inertia below 77 K, the Bare FBG (BFBG) sensor can be coated with high thermal expansion coefficient materials. In this work, different metal were considered for coating the FBG sensor. For theoretical investigation, a double layered circular thick wall tube model has been considered to study the effect on sensitivity due to the mechanical properties like Young`s modulus, Thermal expansion coefficient, Poisson’s ratio of selected materials at a various cryogenic temperatures. The primary and the secondary coating thickness for a dual layer metal coated FBG sensor has been determined from the above study. The sensor was then fabricated and tested at cryogenic temperature range from 4- 300 K. The cryogenic temperature characteristics of the tested sensors are reported.
Through the control system front pressure, temperature, flow rate and other process variables, ADS injector I cryogenic system is operated stably of 4k/2k. We adopts PlC control and EPICS integrate to realize the automatic intelligent control of the superconducting devices. The main function of PLC is building temperature realtime monitor system, logical control system, controlled by using PID of closed loop, safety interlock system, automatic SMS alarm system etc. EPICS is developed to integrate dates from pump system, refrigerator system, cryogenic equipment. This paper describes the ADS injector I cryogenic control system and how this is done.
The Cryomodule Test Facility (CMTF) is a research and development facility, it houses a large state of the art cryogenic plant capable of providing a total of 500W of cooling capacity at 2 Kelvin. Its first test Cryomodule Test Stand (CMTS), 1.5m diameter and 9m long, is to test both 1.3 and 3.9 GHz cryomodules in Continuous Wave (CW) mode for the LCLS-II project. The cryogenic control system includes three subsystems, they are MyCom compressors, Linde super cryogenic plant and CMTS cryomodule cavity. Each subsystem control has to be independently design, but operate integrated together. Therefore, the CMTF multi-level distribution control system consist of two redundancy SIMATIC manager central controls, three Siemens PCS7-400 controllers as subsystem and seven DL205 PLCs as field control. Those authorized remote control centers are to be operate by synoptic HMI through Fermilab ACNET.
This paper presents a method which has been successfully used by many Fermilab distribution cryogenic control systems.
The SuperKEKB accelerator and the BELLE II detector have been developed to conduct high energy physics experiments at KEK.
A remote monitoring system was developed based on the software architecture of EPICS (The Experimental Physics and Industrial Control System) for the cryogenic system of superconducting magnets in the Interaction Region of the SuperKEKB accelerator.
These superconducting magnets are divided into three groups, the BELLE II detector solenoid, QCSL accelerator magnets and QCSR accelerator magnets. They are contained in three separated cryostats. Three helium cryogenic system are used to cool the cryostats respectively.
These cryogenic components of three groups are controlled by Hitachi integrated instrumentation system EX8000 on a dedicated local network from the perspective of security. The developed remote monitoring system enabled the persons concerned to monitor realtime data from the EX8000 on the KEK-LAN (a common local network in KEK) easily and safely. Users also can access and refer the past data easily.
EPICS offered software tools of IO control to communicate with the EX8000 using TCP/IP, archiving techniques using database and easy man-machine interface including various graphical tools.
The remote monitoring system realized to take more than 1000 data at once with the same cycle time of data acquisition as the EX8000. The data includes information of temperature, pressure, liquid-helium level, flow rate, electric current value, valve states and so on of three systems. The realtime and historical graphs, which are same as the EX8000, were made. The graphics displaying the all components of each cryogenic system were also developed to help users grasp the state of the system easily. It enabled users to refer to the same information as those on the EX8000 remotely, through the KEK-LAN.
The automatic control of a helium refrigerator includes three aspects, that is, one-button start and stop control, safety protection control, and cooling capacity control. The 2kW@20K helium refrigerator’s control system uses the SIEMENS PLC S7-300 and its related programming and configuration software Step7 and the industrial monitoring software WinCC, to realize the dynamic control of its process, the real-time monitoring of its data, the safety interlock control, and the optimal control of its cooling capacity. This paper firstly detailed describes the control architecture of the whole system, including communication configuration and equipment introduction; and then introduces the sequence control strategy of the dynamic processes, including the start and stop control mode of the machine; finally tells the precise control strategy of the machine’s cooling capacity, including the safety interlock control strategy of the machine. Besides, in order to realize the unmanned operation, a remote control system is also simply described. Eventually, the whole system achieves the target of one-button starting and stopping, automatic fault protection and stable running to the target cooling capacity.
The European X-ray Free Electron Laser (XFEL) is a research facility and since December 2016 under commissioning at DESY in Hamburg. The XFEL superconducting accelerator is 1.5 km long and contains 96 superconducting accelerator modules. The control system EPICS (Experimental Physics and Industrial Control System) is used to control and operate the XFEL cryogenic system containing the XFEL refrigerator, cryogenic distribution systems and the XFEL accelerator. The PROFIBUS fieldbus technology is the key technology of the cryogenic instrumentation and the link to the control system. More than 650 PROFIBUS nodes are implemented in the different parts of the XFEL cryogenic facilities. The presentation will give an overview of PROFIBUS installation in these facilities regarding engineering, possibilities of diagnostics, commissioning and the first operating experience.
Conservation of helium has become more important in recent years due to global shortages in supply and increasing prices. MRI superconducting magnets use approximately 20% of the world’s helium reserves in liquid form to cool down and maintain operating temperatures at 4K. Efforts are being made to conserve helium in transporting superconducting MRI magnets by shipping them warm and cooling them down at end user locations (i.e. hospitals). These conservation efforts can also be extended to the service model at end user facilities.
This paper describes a mobile cryogenic refrigeration system that has been developed by Sumitomo Cryogenics for this purpose. The system can cool a typical magnet from room temperature to 40K in less than a week. The system consists of four single-stage Displex®-type GM expanders in a cryostat with heat exchangers integrated on the cold ends that cool the helium gas, which is circulated in a closed loop system through the magnet by a cryogenic fan.
The system is configured with heaters on the heat exchangers to effectively warmup a magnet or any remote thermal load. The system includes a scroll vacuum pump, which is used to evacuate the helium circuit with or without the remote load or magnet. Vacuum-jacketed transfer lines connect the cryostat to the magnet. The system is designed with its own controller for continuous operation of precool, warmup and evacuation processes with automatic and manual controls. The cryostat, pumps and gas controls are mounted on a dewar cart. Additionally, the compressors and system control are mounted on mobile carts to increase system flexibility.
The shortage of helium, particularly liquid helium has made the use of cryogen free magnets attractive. The attractiveness of cryogen free device depends on the operating temperature of the device, the distance from the cold head to the device being cooled, the thermal conductivity of the connection, and the size of the object being cooled or cooled down. Connecting a cold source to something being cooled is similar to to connecting a vacuum pump to a device through a long pipe. This report will discuss cooling-down and cooling a device that operates over the temperature range from less than 2 K to 70 K. Two approaches will be discussed cooling using conduction through a high thermal conductivity metal straps and cooling using a thermal siphon cooling loop. The thermal siphon cooling loop can be designed to operate like a conduction cooled cryogen free device, where all of the fluid is stored in the cooling loop.
In the frame of the High Luminosity upgrade of the LHC, improved collimation schemes are needed to cope with the superconducting magnet quench limitations due to the increasing beam intensities and particle debris produced in the collision points. Two new TCLD collimators have to be installed on either side of the ALICE experiment to intercept heavy-ion particle debris. Beam optics solutions were found to place these collimators in the continuous cryostat of the machine, in the locations where connection cryostats, bridging a gap of about 13 m between adjacent magnets, are already present. It is therefore planned to replace these connection cryostats with two new shorter ones and a by-pass cryostats in between where the collimators can be placed close to the beam pipes. The connection cryostats, of a new design as compared to the existing ones, will still have to insure the continuity of the technical systems of the machine cryostat (i.e. beam lines, cryogenic and electrical circuits, insulation vacuum). This paper describes the functionalities and the design solutions implemented, as well as the plans for their construction.
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. This paper examines SMES energy densities of solenoid-type magnets for YBCO, MgB2 and Nb3Sn wires using present-manufactured wires and future advancements predicted from lab samples. Scaling of maximum energy density with the stored energy, length of the conductor and radius of the bore were established with numerical simulations, and studied for a range of stored energies from 0.1 MJ to 250 MJ and operating temperatures of 4.2, 18, 40 and 65 K. With dependence of critical current on field taken into account, the optimum magnet design for varying superconducting wires also including H//c is a pancake coil with scaling of energy density ε ~ E^1/3. Thus, current and magnetics limits achievable ε only at a fixed E. The overall limit on ε is also imposed by the virial theorem. Without additional structural support ε of SMES magnets is limited to ~ 30Wh/kg. However with introduction of light-weight and strong support materials the upper limit MSED of SMES is expected to exceed that of the best batteries ε ~ 150 Wh/kg.
Acknowledgments: Air Force Office of Scientific Research (AFOSR) and The U.S. Air Force Research Laboratory, Aerospace Systems Directorate (AFRL/RQ).
It is envisioned that High Temperature Superconducting (HTS) power cables could replace conventional cables in applications where space and weight are the limiting design factors. In situations where significantly higher power densities (both volumetric and gravimetric) are required and variable power ratings are preferred, it is necessary to operate HTS cables at temperatures lower than the LN2 range. Gaseous helium (GHe) circulation has been demonstrated as a viable option for cooling HTS power cables. GHe has a lower dielectric strength compared to LN2 and low partial discharge inception voltages have been noticed due to the helium gas trapped in the butt gaps of the insulation layers. Recent efforts on enhancing the dielectric strength of GHe by the addition of small mole fraction of hydrogen (H2) have shown that this mixture can double the dielectric strength of pure GHe.
To exploit this phenomena and to avoid the limitations posed by the traditional insulation designs, a new and novel cable design has been proposed where the helium-hydrogen gas mixture acts as both the coolant and insulation medium. Proof of concept experiments demonstrated that the new cable design allows higher operating voltages than what is currently possible as well as have other potential benefits. In terms of dielectric design, this idea is similar to SF6 gas insulated transmission lines (GIL) which operate at room temperature and hence we decided to name it “superconducting gas-insulated transmission line (S-GIL)”. This study extends our previous research and focuses on the optimization of the cable design. Experimental results on the dielectric rating for the different design parameter selected for the gas insulated HTS power cables will be presented. Details of the challenges encountered and innovative solutions devised for the S-GIL design will also be presented.
This work is funded by the Office of Naval Research.
Since energy deficiency and global warming become most serious, it is anticipated global PV installment will reach 230 GW. China has urgent need to use PV to replace its coal-based (over 70%) energy structure. In last 4-5 years China becomes the world largest PV produce and user. Moreover, in China’s plan, about half of the PV electricity are generated from distributed systems, the other half are from Gobi, which has an area of 1.3 million km2 and ample sunshine. In 2012, 9 GW PV power stations are completed in Gobi. Currently the largest PV stations in the world are built in Gobi (about 20 GW). There are still many problems for power transmission from these power stations in deserts. Using HTS transmission lines is promising, while the current density is uniform only within a few meters (not km), which still limit its production yields, resulting in high sale price. Advance HTS technology are still under development for low cost, which are the determined factors for future applications.
It is critical to solve the nonuniform composition problem of the YBCO films by either PVD or CVD for better quality. The composition variations in YBCO affects its critical current density. Therefore, it is challenge to control the YBCO film composition. Also, the pinning issue is still unsolved, and its relationship to the film uniformity is still not understood. In this work, we succeeded in developing Raman scattering as a tool to identify the change of film compositions. We also correlate it with XPS results. Finally we succeed in developing a Metal Organic Sputtering, which adjust the specific MO flows to tune the film compositions. In this work we will report the composition finding using Raman shifts and its correlation with XPS, which will help improve the control of YBCO current density distributions.
Superconducting and cryogenic power system components are understood to have strong advantages for MW-class power systems, such as greatly reduced weight, size and heat loss and increased energy efficiency. In this work, the unique properties and technical readiness assessment of cryogenic and superconducting components will be reviewed, and compared to alternate traditional technologies such as Cu-wire based and semiconducting. For almost every component considered, superconductor devices typically provide 5-10x and sometimes larger reductions of weight and heat loss, and even 3-10x reductions at the system level. There are also other advantages such as greatly increased lifetime and potentially much higher reliability in operation, because of significantly less mechanical degradation from high heat stressing and wear. The improved properties can enable the development of new capabilities for aerospace systems, such as vertical-take-off-and-lift (VTOL) with lightweight components, 2-5x higher improved energy efficiencies from electrical propulsion, and reduced operation noise.
Acknowledgments: Air Force Office of Scientific Research (AFOSR) and The U.S. Air Force Research Laboratory, Aerospace Systems Directorate (AFRL/RQ)
The quick adjustment capability of the excitation system plays a very important role in maintaining the normal operation of superconducting machines and power systems, but the eddy currents in the electromagnetic shield of superconducting machines will hinder the exciting magnetic field change and weaken the adjustment capability of the excitation system. To analyze this problem, a finite element calculation model for the transient electromagnetic field with moving parts is established. The effects of different electromagnetic shields on the exciting magnetic field are analyzed using finite element method. The results show that the electromagnetic shield hinders the field changes significantly, the better its conductivity, the greater the effect on the superconducting machine excitation.
A 6-pole superconducting synchronous generator without electromagnetic shield and with three different electromagnetic shields was calculated using finite element model for the transient electromagnetic field with moving parts. By means of doubling and reversing the exciting coil terminal voltage, the exciting current in the exciting coil of the superconducting machine is changed. The changing process of the magnetic field, the eddy current inside electromagnetic shield and the terminal voltage of the A phase stator armature winding with the exciting current is obtained by calculation. The better conductive property of the electromagnetic shield can improve its shielding ability, but also reduce the excitation adjustment ability of superconducting synchronous machines.
Acknowledgements
This work was supported by the National Nature Science Foundation of China (NO. 51377151).
Thanks to recent advances in flux pinning, current-carrying capacity, and conductor geometry, REBCO tapes are being considered more seriously for high-field magnet applications. However, the material remains intrinsically weak to transverse tensile stresses, and the buffer and/or superconducting layer in the tape can delaminate when subject to such stresses. In this work we use Auger Electron Spectroscopy (AES) to specify the composition of the delaminated layer, and use AES argon sputtering to determine the thickness of the buffer layers in a REBCO film, after fabrication and again in the delaminated layer after mechanical testing. A depth profile is created by alternating Ar sputtering and AES testing. The ratio of yttrium and aluminum (from two buffer layers in the delaminated tape) are compared and a cross-over point is defined (based on sputtering of samples with known buffer layer thicknesses) to allow quantitative comparison of the thickness of the surface buffer layer retained after delamination. Using this approach, the properties of the delaminated layer (such as the chemistry, thickness, and thickness variation) can be determined.
Acknowledgments: This work was financially supported by the U.S. Department of Energy, Office and High Energy Physics, award DE-FG02-13ER42036, and benefited from the support of the Materials Science & Engineering Center at UW-Eau Claire. The authors thank SuperPower, Inc. for providing the samples under investigation.
We will present the status of commercial production of 2G HTS Roebel cables along the advanced “Punch-and-Coat” route.
The “Punch-and-Coat” approach to 2G HTS Roebel cable fabrication was recently developed in collaboration between KIT and SuperOx. The approach is to prepare a meander-shaped strand for Roebel cable by mechanical stamping of silver-finished 2G HTS wire, and then electroplate stabilising surround copper coating onto the strand. As a result, the wire architecture, along the entire strand, is fully encased in copper and is thus geometrically symmetrical and protected from delamination. Moreover, the copper coating, added after punching, smoothens the punching burr on the substrate, making it no hazard for the adjacent strands. The “Punch-and-Coat” strand fully retains its original critical current after 200 thermal cycles between 77 K and room temperature. Before the cable is assembled, the strands are routinely characterised along the entire length by the magnetic non-contact and direct transport critical current measurements at 77 K.
SuperOx has successfully commercialised the fabrication of “Punch-and-Coat” 2G HTS Roebel cables, delivering multiple cables for HTS insert coils for high field accelerator magnets, as well as for stator coils for HTS rotating machines.
Y0.5Gd0.5Ba2Cu3O7-σ (YGBCO) and Ho0.5Gd0.5Ba2Cu3O7-σ (HGBCO) targets of similar density are prepared by solid-state reaction method. These targets are used to prepare superconducting thin film respectively using pulsed laser deposition (PLD). During the experiment, we alter laser energy by changing optical lens. X-Ray diffraction (XRD) is adopted to analyze the structure and texture of R0.5Gd0.5Ba2Cu3O7-σ (RGBCO, R=Y, Ho) thin film. Also, atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used to observe the surface morphology, and superconducting current is measured in 77K by employing standard four-probe method. The laser energy density and different doping element can affect properties of YRBCO thin film, which may be related to target particle ejection process and size of rare earth atoms.
Several improvements on ReBCO tape performance made it possible to reduce tape width and thickness thereby enabling the process of making thin CORC based ReBCO wires. A major improvement has been the reduction of the tape’s substrate thickness from 100 via 50 to 30 micron and even more reduction is expected in the years to come, leading to a lower minimum bending radius of ReBCO tapes. The combination of thinner substrate and narrower tapes allows production CORC wires with enhanced flexibility while maintaining a high current density. It makes CORC round wires suitable for application in all kinds of high field magnets and insert coils. It also opens up the application area of extremely stable magnets operating in 20 to 50 K range. Several CORC wires with different tape layouts were tested in the frame of the CORC wire development program of CERN, ACT and the University of Twente. The 3.0 to 4.5 mm diameter CORC wire samples built with 2 and 3 mm wide tapes are tested as few-turns solenoids at 4.2 K in a magnetic field up to 10.5 T. The tests are performed to demonstrate the ease of use and high performance of the new CORC wires. It also allows optimization of the wire manufacturing process, wire bending procedure and exercising joint terminal production. Step by step wire production has improved and wire flexibility as well as current density increased. Developments are ongoing and further increase in current density and wire flexibility is expected.
Rare-earth cuprate-based (REBCO) superconductors are a family of high-field, high-temperature superconductors fabricated in a tape geometry. The tape structure is composed of a nickel-based Hastelloy substrate base, with oxide buffer layers (to allow for epitaxial growth of the superconductor) and a superconducting film of thickness < 2 μm. The composite is finished with a silver cap layer and a Cu stabilizing layer. One limiting factor for REBCO tapes in a superconducting magnets is the possibility of transverse delamination within the tape; however, the microstructural features that control this delamination behavior are not fully understood. For this study we have developed new sample preparation methods (and subsequent imaging by SEM and laser confocal microscopy) to quantify the damage modes present in delaminated samples. Specifically, we investigate the morphology of the delaminated surface and the retained layers on the tape to ascertain the nature of the crack initiation and propagation. Ultimately, a more thorough understanding of the delamination behavior of this material may lead to improvements in the tape processing to minimize this effect in the future.
Acknowledgments: This work was financially supported by the U.S. Department of Energy, Office and High Energy Physics, award DE-FG02-13ER42036, and benefited from the support of the Materials Science & Engineering Center at UW-Eau Claire. The authors thank SuperPower, Inc. for providing the samples under investigation.
A standard tube-type Nb3Sn conductor was used for the winding of a sub-size MRI-like coil segment. The conductor was 0.8 mm OD and had 217 filaments, with a 45% non-Cu fraction. The wire was twisted, reacted, and then insulated with s-glass. After insulation, the coil was wound on a 1 m OD copper former. The total length of the conductor used was 1.6 km. The coil was instrumented for low temperature testing and then epoxy impregnated. Ten sets of voltage taps and ten thermocouples were used, along with two Cernox sensors and two hall probes (these latter for field measurements). The coil was installed into a large conduction cooled cryobox for cooldown and testing. The coil was cooled by a series of Cu straps which were bolted to the coil ID and then to a Cu cooling ring which was itself connected to two Sumitomo cryocoolers (1.5 W at 4 K each). The coil was surrounded with superinsulation and then sealed in the cryobox. Cool down hit a base temperature of 4 K, with a cool down time of 2 days. A small (1 A) current was applied to the coil during cool down and the coil was seen to have a Tc of 17 K. The maximum temperature difference across the coil was 1.5 K. After the initial cooldown the coil temperature was increased, and Ic was measured as a function of temperature with decreasing temperature. The coil transitioned by n-transition. The radial field of the coil was measured on the former (near the winding) and used to compare coil Ic to short sample Ic via a load line plot.
An important step in the development of fusion as a future power source is the development of plasma facing materials that can function over long periods of time. While ITER and other devices like Wendelstein 7-X and the Joint European Torus will provide insights into divertor and first wall performance, a dedicated device to advance the understanding of material performance in representative plasma environments is needed. The Material Plasma Exposure eXperiment (MPEX) has been proposed as a linear plasma device to generate fusion reactor-like plasma energy and particle flux at the target materials with electron temperatures of 1-15 eV and electron densities of 10^20 to 10^21 m-3. A design study was completed to assess the feasibility of superconducting magnets using materials such as Nb3Sn, NbTi, MgB2, and YBCO from liquid helium to liquid nitrogen temperatures with respect to commercially available conductors. for superconducting magnets need warm bore diameters of 43.2 cm with non-uniform central fields between 0.4 T and 2.4 T. While NbTi was selected for the superconducting magnet due to its low risk the use of MgB2 and YBCO presented unique benefits that could outweigh these risks if certain performance milestones can be met.
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
Nb used in Nb3Sn multifilamentary superconductor wire deforms throughout the fabrication process including the initial extrusion and subsequent drawing, restacking, re-extrusion, and final drawing steps. Unfortunately niobium, usually begins as a 300 mm diameter ingot with extremely large grains. While this ingot gets reduced to a 120-150 mm diameter bar before wire fabrication, the cast macrostructure persists. The result during wire fabrication is often non-uniform Nb – Cu co-deformation, the development non-circular Nb filaments, and the tendency for the filaments to sausage and fracture when the diameter gets small (5-10 microns). To improve conductor performance and meet the needs of advanced magnet applications, larger starting Nb bars and smaller diameter Nb filaments in Nb3Sn strands are needed. This can be accomplished by using highly grain-refined and homogeneous large cross section bars of Nb processed by severe plastic deformation. Microscopy including texture characterizations, and mechanical property measurements are reported on the grain refinement of a 175 mm diameter bar of Grade 1 Nb, to be used to fabricate a prototype multifilamentary Nb3Sn wire. This work presents success with scale-up of a new severe plastic deformation process as applied to starting Nb bar in the Nb3Sn wire fabrication process
This paper studies preparation process and its technology of high RRR value of Wire in channel (WIC) NbTi superconductor wires. It is generally accepted that the lower the oxygen content in the oxygen-free copper, the higher RRR value. In this paper, the results show that the RRR of WIC wire also can achieve relatively high levels under the high oxygen content condition.
Three methods were adopted in this article.
The first method is online annealing on medium frequency furnace, cooling, fluxing, and then soldering using C10100 copper channel wire. When the heating power was higher, the RRR value can meet the requirement of more than 175. But the surface quality of WIC wire and inserting effect were poor.
The second method is using C10100 copper channel wire heat in the vacuum furnace, fluxing, and then soldering. The RRR values of WIC wire were 213-256, with the surface quality and inserting effect were good.
The third method is using C11000 copper channel wire to solder directly. The oxygen content of the selected C11000 copper channel wire ranges from 75 to 200 parts per million (PPM). The RRR value of WIC wire can be improved to 240-260.
In order to study the problem, using C11000 and C10100 to heat at 500 ℃ for 2 hours, and then the microstructure was observed. The C10100 still exist dislocation etc. defects. And the C11000 have no dislocation and other defects basically, which increase RRR values. In addition, the second-phase was found in grain boundary of C11000, which was Cu2O phase.
The oxygen content of C11000 can exist in the form of Cu2O, which do not affect the increase of low temperature resistance. If oxygen element exists in the form of gap element, it will greatly increase the low temperature resistance, and reduce lower RRR value.
Knowledge of thermal-mechanical properties of epoxy-impregnated superconductor/insulation composite is important for designing and fabricating high field superconducting magnets towards their ultimate potentials. As a part of the 15 T dipole magnet program at Fermi National Accelerator Laboratory, we report the study of the mechanical properties and thermal contraction of epoxy-impregnated Nb3Sn Rutherford cable stacks made from the state-of-the-art RRP strands at room temperature and cryogenic temperatures. Stress-strain curves of such composite materials were tested under both monotonic and cyclic compressive loads. The effect of varying the insulation wrapping of the Rutherford cables is also investigated.
Tube type Nb3Sn conductor has been being explored by Hyper Tech Research Inc. Our standard conductor with 217 filament arrays have been generated with 12 T non-Cu Jc values of about 2400-2500 A/mm2 with filament size of 40 micros at the 0.85 mm strand. We also made 547 filament conductor which has filament size of 25 micros at the 0.85 mm strand without any drawing issue. We are working to improve the non-Cu Jc further. In this paper, creating artificial pinning centers has been used to increase flux pinning in order to raise the Jc overall in the 12-20T range within the tube type Nb3Sn strands. As a result, the artificial pinning centers refine the grain size by at least half, thereby increasing the layer Jc by at least 30%. This strand has been made to 61-filament restack and getting filament size of 45 micros at the 0.5 mm strand.
Nb3Sn wire used in accelerator magnets is purchased with a typical specification that copper residual resistivity ratio RRR should be >150, to assure that magnets have adequate thermal conductivity for quench protection. While the primary intention of the specification is to control internal contamination of copper by tin, what is not controlled is external contamination. Standard practice uses pure argon during coil reaction, which is assumed to be a clean environment. This presentation will describe results from strand procurement leading up to the HL-LHC Accelerator Upgrade Project, which cause the cleanliness assumption above to be questioned. Reproducible RRR of ~300 was obtained when 0.85 mm diameter wire samples were protected inside a 1 mm inner diameter quartz tube during reaction, or when reactions were carried out in a scientific high-vacuum furnace. However, RRR values closer to 200, and with much wider scatter, were obtained when the external strand surface was exposed to the argon environment. Evidently impurities in the argon gas or residues of furnace elements and prior heat treatments affect RRR. The difference for protected versus exposed strands has been cross-checked and validated between different furnaces at different laboratories. The presentation also explores whether the insulation on coils offers any protection, which has bearing on project risk. Actual RRR from strands extracted from insulated and exposed cables will be compared to results for raw strands. Analysis of externally introduced impurities in protected and exposed strands by secondary ion mass spectroscopy will also be presented. Guidance will be provided about reaction methods and interpretation of RRR data based on the results.
Traditionally either Niobium, Tantalum or a combination of both have been used as diffusion barriers in Nb3Sn Multi-filament wire. Vanadium has also been used successfully but the ultimate RRR of the copper is limited unless an external shell of Niobium is included. Niobium is preferred over Tantalum when alternating current losses are not an issue as the Niobium is more ductile but will react to form Nb3Sn. Pure Tantalum tends to deform irregularly requiring extra starting thickness to ensure good barrier qualities. Here we report that Tantalum lightly alloyed with Tungsten is compatible with the wire drawing process while deforming as well as or better than Niobium. Ta3wt%W has been processed as a single barrier and as a distributed barrier to fine dimensions. In addition, the higher modulus and strength of the Ta W alloy improves the overall tensile properties of the wire.
This work aims to improve stability of Nb3Sn superconducting wires and magnets by increasing specific heat of Nb3Sn conductors. A technique is put forward to introduce substances with high specific heat (e.g., Gd2O3, whose specific heat capacities are hundreds of times larger than those of Nb3Sn wires at ≤5 K) to Nb3Sn wires. This technique is well compatible with present Nb3Sn wire manufacturing technology. Wires based on this technique have been fabricated and drawn to 25 µm subelement size without breakage. Measurement results demonstrate that this technique can noticeably improve conductor stability, without causing bad side-effects (such as reduced RRR or Jc). This new type of Nb3Sn wires are promising for large-scale applications; compared with conventional Nb3Sn conductors, they are expected to greatly suppress training and instability of superconducting magnets.
In this work we explore the development of an optimum high-Jc multifilamentary (Nb,Ti)3Sn wire containing ZrO2 APCs. First, 61-filament powder-in-tube (PIT) wires containing oxide powders were explored. These wires consist of a Nb-1%Zr tube containing Cu, Sn, and oxide powders. SnO2 and CuO powders were used, and SnO2 was found to release oxygen more readily. These samples were heat-treated at 450°C for 100h and then 650°C for 200h, with a ramp rate of 50°C/h. Incomplete Nb3Sn formation was observed, indicating a need for higher Sn-Nb ratio and longer heat treatment time. New 61 subelement designs were made to achieve higher Sn/Nb ratios; these results are discussed. Next, we performed some initial work in order to develop a ternary wire. In this experiment, an externally oxidized tube-type wire was manufactured, starting from a precursor of Cu-Sn-Ti rod in a Nb-1%Zr tube. Samples were heat-treated in a vacuum sealed quartz tube with CuO present. Heat treatment schedules included 20°C/h up to 650°C for 300h, and 20°C/h up to 700°C for 100h. Grain refinement below 35nm was observed due to the influence of Ti and ZrO2. Then, a 61-filament tube-type wire was produced consisting of a Cu-Sn-Ti rod inside an oxide-containing Nb-Zr tube. Temperature ramp rates of 15, 20, and 30°C/h, as well as several final heat treatment times ranging from 100 to 300 hours at 650°C were evaluated to ensure complete diffusion of O, Ti, and Sn to maximize the quantity of ZrO2 precipitates, composition of ternary phase, and area fraction of fine-grain Nb3Sn, respectively. FG Nb3Sn grain sizes were maintained below 35nm, and superconducting layer Jc above 9600A/mm2 was observed at 4.2K and 12T.
The n value of wire in channel (WIC) NbTi superconductor wires represents the deformation uniformity of internal filament, which is one of the most important properties of superconductor wire. This paper studies the influence of processing methods and test methods on the n value of WIC superconductor wire.
In the processing methods, the filaments positions, filament diameters, twist pitch and processing rate are considered. And the results show that processing methods have no significant influence on the n value. In different filaments positions, the sizes of monofilament are uniform and no foreign body sensation. With the increase of filament diameters, the filament numbers decrease, the n values show no significant changes. And With the increase of twist pitch, the n values show no significant changes. With the increase of processing rate, the n values show no significant changes.
In the low-temperature test methods, many factors are considered. The results show that there have no effects on n value in different outer diameters and different materials of barrel, the connection, sample-preparation and assembling of low temperature part, winding direction in the processing of WIC wire sample-assembling, contact area of current lead. The different groove type of barrel, the slight different sample fastening, and the n value changes slightly. With the increase of loading speed of current, n values have no obvious change. When the current lead of sample holders gives out heat, the n value has no obvious change. Different signal acquisition modes are studied in data and X-Y recorder, the n value has no change. But the lorenz force have important effect on n value. When the direction of lorenz force departs from the barrel center, the n value can increase about three times than the direction of lorenz force towards to the barrel center because the barrel become loose.
An analytical approach is used to calculate the AC losses of round superconducting cables subjected either to external fields applied perpendicularly to the cable length. Losses for fields applied in one fixed direction but varying sinusoidally in time are compared to losses for applied fields with fixed (with time) amplitudes that rotate around the sample (rotating around an axis parallel to the cable length). Such losses are then calculated for fields which both rotate around the sample and have an amplitude which varies with rotation angle. It is shown that rotating fields can be treated as a superposition of orthogonally applied fields in some cases.
The influence of the shape of the strands that make up the cable are explored, with a round strand shape compared to a tape-like geometry. AC losses are divided into hysteresis loss, coupling loss, and eddy current loss, and the effects of both sample and field geometry are explored for each loss component. At last, the proposed analytical method is used to calculate the AC losses of some samples, and the results are compared with those from the numerical simulation based on Comsol Multiphysics and experimental data quantitatively.
A fifteen layer CORC (Cable on Round Conductor) cable, 82 cm long, was tested for stability and normal zone propagation at 77 K in liquid nitrogen bath. The cable had 15 layers, each layer containing 3 tapes, 4 mm wide each. The cable was instrumented with thermocouples, potential taps and wires including as well as excluding its current lug connections. 3 heaters were placed on top of the cable’s central part (one on each tape). The heaters were connected in series and allowed pulses of various powers and durations to be generated. Around the heaters thermocouples were distributed on each tape to measure heating during a quench. DC transport currents of some percentage of the cable critical current (1500 A) were applied. During and after the heat pulse current redistribution among the layers and within the cable current lugs was measured by high speed data acquisition card (DAQ) controlled via LabView software. These results were compared to a Roebel cable measured for quench at 4.2 K in liquid helium and 10 T.
Within the framework to establish standards of test methods for superconducting technical wires, various standards have been published by the International Electrotechnical Commission IEC (standard documents IEC 61788-1 to -20). Following the experience of the successful Round Robin Test RRT for Tensile Test on REBCO Wires at Room Temperature, the effort is extended to Tensile Test on REBCO Wires at Cryogenic Temperatures and is coordinated by CryoMaK lab in KIT. A round robin test is an inter-laboratory test (measurement, analysis, or experiment) performed independently several times in different laboratories. Identical samples are tested using identical or similar test procedure. Results analysis from different participants allows evaluation of the reproducibility of the test method and processes, and the proficiency of participating labs. Different commercially available five ReBCO wires from five different manufacturers and one BiSCCO wire from another supplier are purchased for testing. Materials are provided by VAMAS TWA 16. Samples are distributed between nine participating labs from five different countries. After the measurements are performed according to specified guidelines, the results will be evaluated statistically using F test to investigate the amount of scatter in the test results. The final goal of RRT is to issue an ISO/IEC Standard for cryogenic temperature tensile test for REBCO wires.
In this report the status and details of Round Robin Test on REBCO Wires at Cryogenic Temperatures are presented and discussed.
YBCO coated conductors are of interest in a number of possible High Energy Physics applications, like e.g. high field solenoids for muon colliders. A new approach in making YBCO magnets has been suggested recently, where the coils are neither insulated nor epoxied. It is believed that in this approach, the coil is much easier to protect, because one a given zone becomes normal, the lack of insulation lets it share its current to the next winding layer down. Essentially, the various coil windings are no longer completely in series once a normal zone forms. In principle, the current can be shared across the whole winding, thus essentially serving both to re-route the current, but also to distribute the energy, as quench heaters would in a normal active protection scheme. In the present work we have measured current sharing, stability, quench and normal zone propagation in such a YBCO pancake coil at 4.2 K in liquid helium bath. The experiments have been done in applied magnetic fields up to 10 T at transport currents of a certain percentage of the coil critical current. The coil winding was instrumented for voltage and temperature measurements at several places around the winding, such that both radial and azimuthal quench propagation could be measured. A heater was placed on the inner-most part of the winding. Heat pulses of various powers and durations were generated to measure quench and NZP. Obtained results are compared with our previous measurements on a coil wound using a kapton insulated YBCO tape.
Roebel cables from HTS coated conductors are used in the first real application, in dipole insert magnets for particle accelerators, performed in a work package of the EU-project Eucard2 of CERN. Following-up the first sub-size dipole magnet demonstrator, future full-size magnets require cable designs with significantly enhanced operation currents for favorable magnet impedance, for accelerator magnets as well as for TF-magnets of the future fusion reactor DEMO. The Roebel geometry is quite flexible to enhance the number of strands, either using stacks or increasing the transposition pitch. Both methods however have disadvantages for the application in coils and may lead to higher stress load depending on the coil details.
A proposed new concept extends the existing Roebel cable design by adding an additional Roebel shaped layer of strands around the standard cable resulting in the so-called double core (DOCO) cable. By keeping the strands width constant, the cable cross-section will double in width (12 to 24 mm) and increase in thickness by two layers of coated conductors. The favorable properties of the Roebel cable as full strand transposition and excellent bending ability are nearly completely preserved. An enhancement of the current by more than a factor of 2 is achieved. We demonstrate the feasibility of the concept with a 1.3 kA sub-size cable with experiment and modeling. The effects of parallel and crossed orientation of the two cable parts is investigated. The material for a full width DOCO-cable is under development at industrial partners and the status of the efforts for a full size cable will be reported. The future current carrying potential of the DOCO-approach will be discussed on basis of prototypes and the latest improvements of the industrial coated conductors.
Cable-in-conduit conductor has particular benefits for superconducting magnets. It is rugged and provides cable-level stress management, it has internal flow of cryogen, flared ends can be formed readily and are self-stable once formed. Fabrication of long-length cable presents several challenges: the center tube must be formed and drawn using perforated strip; the cable must be pulled through a long length of seamless sheath tube and then the sheath must be drawn down to compress the wires against the center tube and immobilize them.
Procedures and practical experience for CIC fabrication will be presented.
High temperature superconducting (HTS) cables are expected to play an important role in modernizing the electric power grid. Significant increase in the fraction of renewable power generation is forcing the society to rethink the structure of electrical power grid in the US and elsewhere. Multi-gigawatt capacity long distance DC power transmission and interconnection of the three US power grids are becoming essential for full integration of renewable energy sources and to manage the variability in generation capacity of the renewable sources. The most suitable sites for renewable power generation are typically located far from major load centers, requiring a substantial increase in transmission grid capacity and efficiency. HTS conductor manufacturing has matured and expanded with multiple suppliers around the world. Similarly, HTS cable manufacturing technology has been demonstrated with several demonstrations and installations in the power grid. Cross-country superconducting cables offer many benefits, but have several technical challenges that need to be addressed before making it a reality. This paper presents a study that addresses a few of the challenges for long distance DC superconducting cables: (i) high voltage dielectric and thermal designs, (ii) efficient power electronics and protection systems for multi-terminal DC cables, and (iii) costs associated with the technology. The paper discusses the technical challenges, currently available commercial solutions, gaps in technology, and potential solutions for the outstanding challenges.
The mechanical response of Twisted Stacked-Tape Cables (TSTC) experiencing large Lorentz loads generated during the operation of high-current, high-field magnets was investigated using finite element analysis. In previous work, the numerical analysis of an untwisted 40-tape TSTC under transverse compression was performed to identify cable configurations able to support the tapes against these loads. Two conductor configurations were originally investigated: a stack of tapes inside a solid cylindrical copper rod and a solder filled copper tube. In this paper, an optimization study is performed for the design of the solder filled tube configuration to define an optimal ratio between the thickness of the copper tube and the amount of solder used. A full scale numerical model of a twisted stacked cable is also analyzed and the results are compared with previous findings for the untwisted configuration. In addition, a study on the stress distribution inside a cable as a function of the tape width is conducted to highlight the advantages and disadvantages of using a wide tape compared to a narrow tape. Finally, based on the findings of the mechanical response of these cable configurations subjected to large Lorentz loads, the critical current performance of the TSTC conductors is discussed.
For the high luminosity upgrade of the large hadron collider the US accelerator research program is developing the quadrupole magnet MQXF wound with a 40 strand (N = 40) Nb3Sn Rutherford cable QXF. During the field ramping of accelerator magnets interstrand coupling currents flow through the crossover- and adjacent-strand contact resistances represented by Rc and Ra, respectively, and a combination of them by Reff. In order to control Rc during reaction heat treatment (RHT) thin stainless steel cores of specified widths (core cover, W%) are often included in Nb3Sn Rutherford cables. Cables with cores of various widths were prepared and reaction heat treated (RHT) under various conditions. In earlier studies by our group the cables were RHT under face-on uniaxial pressure of 20 MPa and vacuum impregnated with resin under 5 MPa. The close crossover contact produced an uncored average Rc of 0.26 μΩ. But with increasing core width Reff(Rc,Ra) increased rapidly reaching, for example, more than 240 μΩ at W ~ 90%. Reff versus W% results for QXF cable stacks agreed with prediction based on the fortran code CUDI(c) assuming Rc = 0.26 μΩ and 1000 μΩ for the uncored and cored contact, respectively. More recently cable RHT and vacuum impregnation in the absence of mechanical constraint has been recommended; the magnet winding or test cable stack is placed in a closed channel just large enough to contain it during RHT when small known expansions in both width and thickness occur. Reff versus W% results for QXF cable stacks treated in this way are compared with the earlier experimental results and the fortran prediction. It was deduced that crossover contact was absent (Rc essentially infinite) and that Reff which did not vary much with W% depended entirely on Ra (of order 20 nΩ) following the relationship Reff = (N3/20)Ra.
The James Webb Space Telescope (JWST) is the largest cryogenic instrument/telescope to be developed for space flight. The telescope will be passively cooled to < 50 K and the instrument package will be at 40 K with the mid-infrared instrument at 6 K. The final cryogenic test of the Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) as an assembly (OTE + ISIM = OTIS) will be performed in the largest 15 K chamber in the world, Chamber A at Johnson Space Center. The planned duration of this test will be 100 days in the middle of 2017. Needless to say, this ultimate test of OTIS, the cryogenic portion of JWST will be crucial in verifying the end-to-end performance of JWST. A repeat of this test would not only be expensive, but would delay the launch schedule (currently October 2018). Therefore a series of checkouts and verifications of the chamber and ground support equipment were planned and carried out between 2012 and 2016. This paper will provide a top-level summary of those tests, trades in coming up with the test plan, as well as some details of individual issues that were encountered and resolved in the course of testing.
The James Webb Space Telescope (JWST) is a cryogenic observatory that will provide unprecedented views of our universe. The spacecraft instruments are primarily cooled via passive cryogenic radiators. Ball Aerospace was responsible for designing, building and testing three of these radiators, the Fixed ISIM Radiators (FIR), with the largest designed to dissipate nearly 0.5W at 40K with a radiating area of 4.6m2. This paper will discuss the unique challenges in the design and fabrication of the FIR, and how these challenges were overcome to meet system requirements and deliver radiators with an emissivity of greater than 0.96 at 40K and 95% efficiency. Additionally, this paper will provide details on the thermal balance test design, which includes a large space background simulator with an emissivity of 0.98 at 13K. Testing results will also be provided which verified the performance and capacity of each radiator prior to delivery for integration on the JWST spacecraft.
We report a thermal analysis of a polarization modulator for use in a space-borne cosmic microwave background (CMB) project. A measurement of the CMB polarization allows us to probe the physics of early universe and currently this is known to be the best candidate to test the cosmic inflation experimentally. One of key instruments to achieve this science is to use a polarization modulator. The polarization modulator unit (PMU) consists of an optical element, called half-wave plate (HWP). The HWP has to rotate continuously at about 1 Hz below 10 K to minimize its own thermal emission to a detector system. A mechanical bearing produces friction, which becomes a source of heat to the cryogenic environment. The continuously rotating HWP system at cryogenic temperature can be realized by using a superconducting magnetic bearing (SMB) without significant heat dissipation.
While the SMB achieves the smooth rotation due to the nature of contactless bearing, estimation of a HWP temperature becomes challenging. We manufactured a one-eighth scale prototype model of PMU. We built a thermal analysis model based on the experimental thermal performance using the scale model and forecasted the projected thermal performance of PMU for a full-scale model based on the thermal model. From this analysis, we discuss the design requirement toward constructing the full-size model for use in a space environment.
This work is a part of study to design and build a PMU for a future CMB satellite mission, such as LiteBIRD.
NASA has completed a series of tests at the Kennedy Space Center to demonstrate the capability of using integrated refrigeration and storage (IRAS) to remove energy from a liquid hydrogen (LH2) tank and control the state of the propellant. A primary test objective was the keeping and storing of the liquid in a zero boil-off state, so that the total heat leak entering the tank is removed by a cryogenic refrigerator with an internal heat exchanger. The LH2 is therefore stored and kept with zero losses for an indefinite period of time. The LH2 tank is a horizontal cylindrical geometry with a vacuum-jacketed, multilayer insulation system and a capacity of 125,000 liters. The closed-loop helium refrigeration system was a Linde LR1620 capable of 390W cooling at 20K (without any liquid nitrogen pre-cooling). Three different control methods were used to obtain zero boil-off: temperature control of the helium refrigerant, refrigerator control using the tank pressure sensor, and duty cycling (on/off) of the refrigerator as needed. Summarized are the IRAS design approach, zero boil-off control methods, and results of the series of zero boil-off tests.
Launch vehicle propellants can be densified by an external thermodynamic vent principle operating sub-atmospheric pressure and benefits the space launch industry by reducing vehicle gross liftoff weight (1). However, this principle requires compressors to generate significant head (0.1 bara inlet to 1.1 bara discharge for hydrogen) which can either be achieved by high shaft speed or by multiple compression stages. Traditional propellant densification systems utilize compressors with grease packed ball bearings which limit shaft speed thereby driving the system design toward multiple compression stages and greater complexity while also shortening service intervals. In association with a NASA Small Business Innovative Research (SBIR) initiative to improve this process, Barber-Nichols Inc. (BNI) developed and tested liquid hydrogen lubricated foil bearings in a high-speed hydrogen gas compressor for the production of densified launch vehicle propellants. Foil bearings do not have the same shaft speed limitations allowing the compressor to run faster reducing the number of compression stages and simplifying the propellant densification system. The test results are presented here.
Recent demonstration of advanced liquid hydrogen storage techniques using Integrated Refrigeration and Storage (IRAS) technology at NASA Kennedy Space Center led to the production of large quantities of densified liquid and slush hydrogen in a 125,000 L tank. Production of densified hydrogen was performed at three different liquid levels and LH2 temperatures were measured by twenty silicon diode temperature sensors. System energy balances and solid mass fractions are calculated. Experimental data reveal hydrogen temperatures dropped well below the triple point during testing, and were continuing to trend downward prior to system shutdown. Sub-triple point temperatures were seen to evolve in a time dependent manner along the length of the horizontal, cylindrical vessel. The phenomenon, observed at two fill levels, is detailed and explained herein. The implications of using IRAS for energy storage, propellant densification, and future cryofuel systems are discussed.
The European X-ray Free Electron Laser (XFEL) is under commissioning at DESY. The superconducting XFEL linac will produce pulsed electron beam with energy of 17.5 GeV. The linac consist of 800 superconducting niobium 1.3 GHz nine cell cavities and 100 superconducting magnet packages assembled in 100 cryomodules. Each cryomodule has 12 m length and includes the 2K helium II bath circuit for the cavities and two radiation shields at temperatures of 5-8K and 40-80K. Before installation in the XFEL linac tunnel all cryomodules were tested in the Accelerator Test Facility (AMTF).We report about methods and results of static and dynamic heat load measurements of all XFEL cryomodules in AMTF and compare with first integral heat load mesurements in the XFEL linac.
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) is preparing for the Proton Power Upgrade (PPU) project to increase the output energy of the accelerator from 1.0 GeV to 1.3 GeV. As part of this project with the combination of increasing the output energy and beam current, the beam power capability will be doubled from 1.4MW to 2.8MW. In this project, seven new high beta cryomodules housing 28 superconducting niobium cavities will be added to the LINAC tunnel. Lessons learned from over ten years of operation will be incorporated into the new cryomodule and cavity design. The design and the fabrication of these cryomodules and how these will be integrated into the existing accelerator will be detailed in this paper.
Fermilab’s 1.3 GHz prototype cryomodule for the Linac Coherent Light Source Upgrade (LCLS-II) has been tested at Fermilab’s Cryomodule Test Facility (CMTF). Aspects of the cryomodule design have been studied and tested. The cooldown circuit was used to quickly cool the cavities through the transition temperature, and a heater on the circuit was used to heat incoming helium for warmup. Due to the 0.5% slope of the cryomodule, the liquid level is not constant along the length of the cryomodule. This slope as well as the pressure profile caused liquid level management to be a challenge. The microphonics levels in the cryomodule were studied and efforts were made to reduce them throughout testing. Some of the design approaches and studies performed on these aspects will be presented.
This paper describes the initial operational experience gained from testing Linac Coherent Light Source II (LCLS-II) cryomodules at Fermilab’s Cryomodule Test Facility (CMTF). Strategies for a controlled slow cooldown to 100K and a fast cooldown past the niobium superconducting transition temperature of 9.2K will be described. The test stand for the cryomodules at CMTF is sloped to match gradient in the LCLSII tunnel at Stanford Linear Accelerator (SLAC) laboratory, which adds an additional challenge to stable liquid level control. Control valve regulation, Radio-Frequency (RF) power compensation, and other methods of stabilizing liquid level and pressure in cryomodule 2.0 K SRF cavity circuit will be discussed. Several different pumping configurations using cold compressors and warm vacuum pumps have used on the cryomodule 2.0 K return line and the associated results will be described.
Thermoacoustic Oscillations (TAOs) are a well known phenomenon in cryogenics and in most cases is an undesirable effect. During LCLS-II prototype Cryomodule testing, TAOs were observed in both the Cryogenics Distribution System and in the LCLS-II Cryomodule JT and Cooldown Valves. The TAOs manifested themselves through the usual effect of added heat load to the cryogenic system and ice formation on the oscillating device. However, during cavity testing, the TAOs were also found to negatively affect microphonics detuning of the SRF cavities. Systematic studies were carried out and it was discovered that the TAOs could be "turned off" or substantially decreased by operating at subcritical pressures on the supply. Lastly, various dampening techniques were employed to allow operations at supercritical pressure with improved microphonics and reduced heat load.
NASA is designing an unmanned submarine to explore the depths of the hydrocarbon-rich seas on Saturn’s moon Titan. Data from Cassini Huygens indicates that the Titan polar environment sustains stable seas of variable concentrations of ethane, methane, and nitrogen, with a surface temperature around 93 K. The submarine must operate autonomously, study atmosphere/sea exchange, interact with the seabed, hover at the surface and at any depth within the lake, and be capable of tolerating different concentration levels of hydrocarbons. One of the major challenges with the thermal portion of the design is predicting the degree of nitrogen gas effervescence within the multicomponent sea (due to heat from the submarine) and the impact of nitrogen gas bubbles on science instruments, ballast systems, and submarine propellers. Effervescence measurements on various liquid methane-ethane compositions with dissolved gaseous nitrogen are presented from 20 psi to 80 psi at temperatures from 92 K to 96 K to simulate the conditions of the seas. These experimental effervescence measurements will be used to update the current design the Titan Submarine.
Application of partial pressure technology to combinations of one gas above its critical temperature (helium) mixed with a two-phase liquid (nitrogen) can result in liquid temperatures down to and below the nitrogen triple point. The thermodynamics of this process is developed and an experimental apparatus is described which was used to produce a helium/nitrogen bath temperature of 59.17 K, 4 K lower than the 63.2 K nitrogen triple point and lower than any liquid nitrogen temperature reported in the literature.
In this study, we use the Langmuir probe plasma diagnostics technique to investigate the dielectric properties of gas mixtures for cryogenic applications. In our previous studies we reported substantial enhancement in the dielectric strength of gaseous helium by adding small mole fractions of gaseous hydrogen. We performed the Boltzmann analysis to predict the dielectric strengths of several helium-hydrogen gas mixtures and validated the theoretical results by breakdown measurements conducted at 77 K and pressures up to 2 MPa. The present study uses the Langmuir probe, a well-known plasma diagnostics method, to obtain basic plasma characteristic parameters that represent the dielectric properties of gas media. The coefficients of electron kinetic processes such as the ionization and attachment coefficients are derived based on the measured electron energy distribution function and the electron scattering cross sections of helium and hydrogen. This paper presents the details of the Langmuir probe plasma measurements, the derivation of the ionization and attachment coefficients, and the comparison between the results of the Langmuir probe method and those of our previous studies.
This study investigates the dielectric strength of cryogenic gas mixtures containing helium, hydrogen, and nitrogen under the operating conditions of a continuous cryogenic cooling loop for shipboard power systems. Substantial enhancement in the dielectric strength of gaseous helium, a relatively weak dielectric medium compared to liquid nitrogen, the standard cooling medium for high temperature superconducting devices, has been achieved by adding various mole fractions of gaseous hydrogen and nitrogen as reported in our previous studies [1—3]. The continuous cryogenic cooling loop for shipboard power systems consists of several sections including those of power generation, power distribution, and power conversion, each operating at its optimum operating temperature. In the present study, we extend our investigations to the various cryogenic operating conditions of each section in the continuous cryogenic cooling loop. This work includes the estimation of the dielectric strengths of the cryogenic gas mixtures and maps the feasible mixtures of helium, hydrogen, and nitrogen gases with the goal of identifying those with highest dielectric strength. We conduct the Boltzmann analysis to estimate the dielectric strength of the gas mixtures in terms of the electron energy distribution function and the coefficients of electron kinetic processes. The chemical phase equilibrium is solved in this study to map the mole fractions of helium-hydrogen-nitrogen gas mixtures, which can serve as a cooling and dielectric media without condensing the hydrogen or nitrogen in the mixture. The study results serve as a practical guideline for the dielectric design of gas-cooled shipboard cryogenic systems containing superconducting power devices.
Prototypes of gaseous helium cooled High Temperature Superconducting (HTS) power cables and other high power density devices have been demonstrated. Additional superconducting power applications cooled with closed loop helium circulation are being explored either to exploit the higher power density of HTS cables at low temperatures (< 77 K) or to utilize superconducting materials such as MgB2 with lower Tc values. One of the challenges posed by gaseous helium is its low dielectric strength. We have reported significant enhancement of dielectric strength of gaseous helium when 4 mol% of hydrogen gas added [1,2]. We have extended this work with systematic studies on the effect of hydrogen mol% on the dielectric strength in an attempt to optimize the gas mixture that will further enhance the dielectric properties without causing safety concerns of the flammability. Studies have also been undertaken on tertiary gas mixtures containing hydrogen, helium, and nitrogen. Theoretical modelling of the tertiary mixtures predicts a significantly higher dielectric strength than pure helium. Details of the experiments, results of the variation of dielectric strength of the binary and tertiary mixtures compared to pure helium gas are presented.
The work is funded by the Office of Naval Research.
Many high temperature superconducting (HTS) power devices have been successfully demonstrated in the power grid. Most of the HTS devices are cooled using liquid nitrogen as the cryogen. Gaseous helium is being explored as a viable option for cooling HTS power devices where higher power density is required making the operation at temperatures less than 65 K is necessary. Helium gas is versatile in terms of the operating temperature of HTS systems. However, challenges in using helium gas as a cryogen exist due its weak dielectric strength and volumetric low heat capacity compared to that of liquid nitrogen. Gaseous helium mixed with small mole fractions of hydrogen has been shown to have enhanced dielectric strength. To be an effective cryogenic medium for HTS power systems with required cooling power, gaseous helium systems typically operate at pressure of over 1 MPa. When considering to use helium gas mixtures, it is essential that the additives such as hydrogen for helium gas need to preserve the thermal characteristics of pure helium gas. Thermal conductivity of high pressure gas mixtures at cryogenic temperatures is not available and is not easy to estimate using mixing theory. In this study, cryogenic thermal conductivity was measured experimentally for pure helium gas and helium gas mixtures containing up to 4 % volume fraction of hydrogen at 77 K and pressures higher than 1 MPa. These thermal properties would be useful for identifying a gas mixture with optimal dielectric and thermal characteristics essential for using the mixtures as cooling media for HTS power applications. Results of the experimental studies on thermal characteristics of gaseous helium mixtures are presented and their implication in gas cooled HTS applications is discussed.
A transient model for a cryogenic carbon dioxide capture (CCC) pump is presented. The pump separates carbon dioxide by desublimation from nitrogen in the gas mixture exhaust from power plants. Compared with other CCC methods, desublimation is commonly considered to be competitive when the concentration of carbon dioxide is low. It is necessary to explore the fully detailed physical mechanisms associated with the flow as well as mass and energy conservation. The pump is modeled as a tube-in-tube counter-flow heat exchanger including four control volumes, the nitrogen (or helium) coolant, the wall, the solid carbon dioxide layer and the mixture. The main task of the model is to study the speed and location of deposition and the capacity of the pump based on thermodynamics combined with numerical analysis. In order to verify the model, deposition processes under various pump conditions are simulated and the simulation results are compared with corresponding calculations that do not consider the solid carbon dioxide layer and with experiment data. The results demonstrate an improved accuracy by taking the solid layer into consideration. The model captures a variety of deposition parameters, and gives primary attention to the role of the frost deposition rate. The analysis approach also provides generic value to other systems with a gas-solid phase change.
Minor geometric features and imperfections are commonly introduced into the basic design of multi-component systems in order to simplify or reduce the expense of manufacturing. In this work, detailed 3D Computational Fluid Dynamic (CFD) models were used to investigate the impact of such apparently minor geometric imperfections on the performance of Stirling type pulse tube cryocoolers. A series of CFD simulations based on a prototypical cold tip was carried out. Temperature and velocity distributions in perfect and imperfect geometries were compared and analyzed. Predictions of cooling performance and gravity orientation sensitivity were compared with experimental results obtained with cryocooler prototypes. The results indicate that minor geometry imperfections in cold tip assembly can have considerable negative effects on the gravity orientation sensitivity of pulse tube cryocooler.
A novel type of PZT-based compressor operating at mechanical resonance, suitable for pneumatically-driven Stirling-type cryocoolers, was presented at CEC-ICMC 2015. The detailed concept, analytical model and the test results on the preliminary prototype were reported earlier and presented at ICC17. Despite some mismatch between the impedances and insufficient structural stiffness, this compressor demonstrated the feasibility to drive our miniature Pulse Tube cryocooler MTSa, operating at 103 Hz and requiring an average PV power of 11 W, filling pressure of 40 Bar and a pressure ratio of 1.3.
At ICC19 the prototype of a miniature passive warm expander (WE) was presented. The WE mechanism included a phase shifting piston suspended on a silicone diaphragm, a mass element, and a viscous damping system. Several technical drawbacks prevented perfect matching between the WE and MTSa; however, the presented prototype proved the ability to create any flow-to-pressure phase appropriate for a PT cryocooler.
This paper concentrates on integration of the MTSa cryocooler with the recently modified PZT compressor operating at corrected mechanical resonance and the modified WE, which was also updated recently to match the MTSa requirements.
High capacity Stirling-type pulse tube cryocooler (PTC) has promising application in high temperature superconductor cooling and gas liquefaction. However, with the increase of cooling capacity, its performance deviates much from that simulation by well-accepted one-dimensional model, such as Sage and Regen, mainly due to the strong field nonuniformity. In this study, several flow straighteners placed at both ends of the pulse tube are investigated in order to improve the flow distribution. A two-dimensional model of the pulse tube based on the computational fluid dynamic method has been built to study the expansion efficiency of the pulse tube under different flow straighteners including stainless steel screens, copper screens, taper transition and taper copper slots. The gas temperature, flow and pressure distributions are compared and analyzed. A PTC set-up which has more than one hundred watts cooling power at 80 K has been built and tested. The flow straighteners mentioned above have been applied and tested. The results showed that with the best flow straightener, the cooling performance of the PTC can be significantly improved. Both CFD simulation and experiment show that the straighteners have much great impacts on the flow distribution and the performance of the high capacity PTC.
An inertance tube is widely used to provide appropriate impedance at the warm end of the pulse tube in pulse tube refrigerator (PTR). The inertance tube is usually coiled around the outer surface of a linear compressor or in a reservoir to reduce installation space, which affect the cooling performance. The materials of the inertance tube would also influence the pressure drop of the helium gas within inertance tube and change the phase angle between pressure and mass flow. The influences are dependent on the operating frequencies. A numerical model is built to simulate the cooling performance of the PTR with different coiled types and materials (copper and stainless steel) operating at different frequencies. The results show that the phase shift ability of the inertance tube would decrease while increasing the number of coiling turns, which cause more PV power for the same cooling capacity. More PV power would also consume while change the material of the inertance tube from stainless steel to copper. The differences will be weakened while increasing the operating frequency. The results provide a new perspective that why the inertance tube can have better applications under higher frequency. Experiments are performed to verify the simulation results.
By using a well-designed transmission tube to recover the dissipated acoustic power at the hot end of the former PTC, the efficiency of the multi-stage cascade PTC is capable to approach Carnot efficiency. Based on this theory, a third pulse tube cryocooler (PTC) was connected in series with the existing two-stage cascade PTC. Experiments showed that the cooling power of the three-stage cascade PTC was 253.6 W @233 K, which was improved by 39.9% compared with that of the single-stage PTC. This moved the PTC efficiency forward one more step to approach Carnot efficiency.
Multi-stage pulse tube cooler normally uses U-type configuration. For compactness, it is attractive to build a completely co-axial multi-stage pulse tube cooler. In this way, annular shape pulse tube is inevitable. Although there are a few reports about annular pulse tube used in a cooler system, a detailed study and comparison with a circular pulse tube is lacking. In this paper, a numeric model based on CFD software is firstly carried out to compare the annular pulse tube and circular pulse tube used in a single stage in-line type pulse tube cooler with about 10 W cooling power at 77 K. The length and cross sectional area of the two pulse tubes are kept the same. The simulation results show that enthalpy flow in annular pulse tube is lower by 1.6 W (about 11% of the enthalpy flow) than that in circular pulse tube. Flow and temperature distribution characteristics are also analyzed in detail. Experiments are then conducted for comparison on an in-line type pulse tube cooler. With the same acoustic power input, the pulse tube cooler with a circular pulse tube obtains 7.88 W cooling power at 77 K, while using annular pulse tube leads to a cooling power of 7.01 W, a decrease of 0.9 W (11.4%) on the cooling performance. The study sets the basis for building a completely co-axial two-stage pulse tube cooler.
With the development of the pulse tube refrigerator, the efficiency increasing meets a technology neck with traditional phase shifter such as double inlet or inertance tube. A displacer as phase shifter is one method to overcome this problem. The displacer with a rod is the ideal phase shifter till now, the phase adjustment is free, and the stroke can be controlled by the rod diameter. Unlike Stirling refrigerator in which the diameter of the displacer is limited by the diameter of the cold finger, the diameter of the displacer in the displacer pulse tube refrigerator is free for design. The diameter effect of the displacer is investigated by numerical simulation, which shows that the diameter of the displacer with optimum displacer rod diameter has no big influence to the efficiency and cooling power while the stroke decreasing with the increasing of the displacer diameter. The regenerator length effect to the displacer is also investigated, too
We describe the general design and development progress of a cryogenically cooled 1-MW inverter. The goal is to achieve an efficiency of 99.3% at 500-kW power and a specific power of 26 kW/kg. The design must be compatible and scalable with cooling by both liquid hydrogen and liquid natural gas, but the experimental prototype will be cooled by liquid nitrogen. The input dc voltage is 1000 V, and the output frequency is 200-3000 Hz. The inverter requires sufficient filters to meet DO-160 EMI standard, and both conventional and superconducting inductors were evaluated for this purpose. The candidate commercial off-the-shelf power semiconductors were characterized from 77 K to room temperature for on-state resistance, breakdown voltage, and switching energy loss. The inverter design uses a three-level active neutral-point clamped topology that uses different power switches for the fast and slow switching. A calorimeter was developed that can measure the efficiency of the 200-kW and 1-MW prototypes by the dissipated losses to the liquid nitrogen to better than 0.1% of the total power. Phase I of the project is complete, with a design that meets the project goals. Phase II of the design is ongoing with fabrication of a 200-kW inverter to reduce the risk of key design elements. Phase III of the project will be construction and test of the 1-MW inverter.
This project was partially funded by NASA AATT under Contract No. NNC15AA01A.
Cryogenic Power Electronics, or CryoPower, has been proposed as an innovation for over two decades as a means of integrating power electronics and superconducting devices, particularly magnets, motors, and generators at cryogenic temperatures close to the operational temperature of superconductors. In these systems, power electronics specifically designed to operate in the cryogenic environment are installed in cryostats and in close proximity to superconducting devices. Among the benefits of cryogenic operation of semiconductors are reduced conduction losses, increased switching times, higher power density (reduced size and weight), and reduced system-level losses. Potential applications include wind turbines, maglev, all-electric aircraft and ships, utility-scale energy storage and transmission and distribution, and power systems for advanced computers, all of which may benefit from superconductivity in one form or another. Much progress has been made recently in scaling prototypes to commercial power levels.
To make CryoPower attractive, a large number of ancillary hardware and electronic components qualified for cryogenic operation is required. Most electronic components are not qualified to operate over an extreme temperature range. Consequently, difficult choices must be made and extensive testing is required to meet the demands of even a simple circuit. In addition, testing of circuits and sub-circuits often requires several cooling cycles, which must be done in a controlled fashion. As a consequence, development is much slower and more tedious than for room temperature circuits. However, this is a necessary process because of the critical reliability demands of power networks.
MTECH will summarize its most recent progress in developing fully integrated CryoPower systems, including development of a Superconducting Magnetic Energy Storage (SMES) system.
GaN-based field-effect transistors have shown great potential in the development of high-density power converters and also hold promise for cryogenic applications. In order to explore this potential, the cryogenic performance of an EPC gallium-nitride (GaN) power field-effect transistors (FETs) has been evaluated. At -195 C, an 85 % reduction in on-state resistance, and a 16 % increase in threshold voltage were experimentally measured without observing carrier freeze-out effects. Moreover, using a double-pulse test, no major changes in switching characteristics were noted.
Building on these results, a 1 kW, GaN-based, 3-level power converter was designed and successfully tested from room temperature down to -140 C, using a custom milled cold-plate. At -60 C, a 16% reduction in losses was achieved at rated power. An estimated power loss breakdown was performed by taking into account the decreasing conduction losses of the GaN FETs and estimates of losses for the passive components. It is clear that there is significant opportunity for additional gains in efficiency by combining high-performing GaN FETs with passive components optimized for low temperature operation. This work is the first demonstration of a flying capacitor multi-level converter and associated components at such low temperature, and highlights opportunity for further gains in density and efficiency in liquefied natural gas applications which offer readily available low temperature cooling.
Next generation electric power systems on Navy ships require higher capacity, efficiency, and stability to meet the demands of increasingly complicated grid systems. High-temperature superconducting (HTS) Conductor on Round Core (CORC®) power transmission cables provide unique solutions by offering high operating currents and current densities in a very small cable cross-section. Advanced Conductor Technologies is developing 2-pole dc and 3-phase ac power transmission cables, cable terminations and connectors to be cooled with pressurized cryogenic helium gas for shipboard use. The development and initial test results of 2-pole dc CORC® power transmission cables, rated at 4,000 A per phase, will be discussed. The development is not limited to only the power transmission cables, but also includes CORC® feeder cables that form the connection between the room temperature bus bar and the CORC® power transmission cable located inside the helium gas environment. Methods to significantly increase the current rating to exceed 10 kA per phase, and current densities of over 500 A/mm2 will be discussed. Efforts are underway to develop advanced dielectrics that are sealed against helium gas penetration, to enable operation of superconducting power transmission cables at a voltage in the order of 10 kV or above, resulting in a cable power rating of 10-100 MW.
As desired for a sustainable economy, efficient renewable energy generation, conversion, distribution, and storage technologies are indispensable to meet society’s increased need in energy utilization. Propulsion is one of the major functions the modern society needs, and electric-propulsion, rather than internal combustion based propulsion, will be a key player to help reach the goal of sustainability by directly linking the renewable energy sources to energy applications.
Unlike other energy storage means available, electricity storage in the form of electric current provides potential advantages of high performance, high conversion efficiency, and unique capability to meet high demand in power output in energy applications. Superconductivity at reasonable cryogenic temperatures will provide the foundation to develop energy related technologies.
This presentation will briefly overview some current effort in developing SMES as a means of energy storage that can be applicable in areas of hybrid-electric propulsion, power conditioning for a microgrids, and pulsed power source development for special energy applications. An example will be given for a first generation of HTS solenoid magnet design, fabrication, and test as an integrated SMES system.
Electrical energy storage devices are critical components of electric power systems of every aerospace vehicle. They are needed for many functions, such as to provide high-power for pulsed loads, as an electrical accumulator unit (EAU) to handle transient loads both on/off the buses, for emergency power during generator or hydraulic-system failure, and as a high-capacity energy source for hybrid-electric-vehicle (HEV) or electric-vehicle (EV) propulsion. Hybrid-electric propulsion for airborne vehicles is understood to provide significant energy efficiency benefits, including during taxiing, for climb, cruise and descent phases, and regenerative (regen) power during descent which has been successfully demonstrated. As electric propulsion of aircraft progresses to 1-10 MW expected in the next 5-10 years, SMES is considered one of the few technology options that can provide high power capability particularly for fast charging, with reasonable weights. SMES along with supercapacitors are the only two technologies able to provide pulsed power for railgun applications, and to handle MW-class transient pulse loads such as high-energy-laser (HEL) shots or absorb high-power-system-faults.
Superconducting-magnetic-energy-storage (SMES) devices offer attractive and unique features for airborne vehicles including the highest power densities known achievable for any technology of 10-1000+ kW/kg for both charge and discharge, 100% storage efficiencies for unlimited times, and for some designs virtually no degradation for up to 10^8 charge/discharge cycles. The energy density of SMES was traditionally < 10 Wh/kg, however recent computational investigations indicate the energy densities could reach > 100 Wh/kg and be competitive with Li-batteries. This paper will describe about the functions of SMES for aerospace electric propulsion, and provide a recent update on the development and performance of SMES devices being designed and built. In-house computation of the design of SMES devices optimized for mass-specific energy densities will be shown, and compared with devices presently existing or being developed.
Over the past couple of years we have carried out the thus far most extensive neutron irradiation study on Nb3Sn. Samples of five types of state-of-the-art multifilamentary wires as well as high-purity polycrystals were exposed to sequential fast neutron irradiation in the TRIGA Mark-II reactor in Vienna. Irradiation induced changes in the superconducting properties were assessed by means of magnetometry and transport measurements, and transmission electron microscopy was used to examine the defect structure resulting from the particle bombardment. We found a large increase in the volume pinning force up to very high neutron fluences, which can be described using a two-component pinning force model. Within this model irradiation induced defects are treated as point-like pinning centers, which enhance the original grain boundary pinning landscape. We put our results into context with other irradiation studies, and argue that the concept of pinning landscape enhancement through nano-scale defects should be transferrable to an industrial production process.
The record Jc of Nb3Sn conductors has plateaued since the early 2000s; however, new target has been put forward for the planned future circular colliders. This presentation aims to discuss prospects for further improvement of Nb3Sn conductors. The factors determining the non-Cu Jc are summarized, which include current-carrying Nb3Sn fraction in subelements, Nb3Sn Bc2, and pinning capacity; then prospects to improve each factor are analyzed respectively. A model is introduced for phase fractions in subelements; the limit of current-carrying Nb3Sn fraction in subelements is obtained based on this model. A model is also proposed to explore what determines Nb3Sn phase stoichiometry during diffusion reaction. It is seen that among all the possible means, the only opportunity for significantly improving non-Cu Jc relative to the present record values lies in improving pinning. To improve pinning, a comprehensive review of an internal oxidation technique is given in this talk, including its opportunities, challenges, and its applications in major types of Nb3Sn wires (PIT, RRP, and single-barrier wires). Recent progress in optimizing this method for further improving the performance of Nb3Sn conductors is also reported.
The heat treatment of internal tin Nb3Sn wires has historically used multiple low temperature stages designed to mix the Cu and Sn as to minimize liquid contact with the Nb filaments, to inhibit Kirkendall void formation, or to increase the Sn concentration surrounding the Nb filaments prior to the A15 reaction. Our recent studies have shown that the unique geometry of high-Jc RRP® wires, where Nb filaments in a Cu matrix are densely packed around the Sn core, benefits from a very different approach to optimization. In such wires the low Cu:Sn ratio requires the Cu-Sn mixing to occur within the sub element cores. This is facilitated by the early formation of a membrane-like ring of the Sn Nb Cu ternary phase Nausite around the core that allows Cu diffusion from within the filaments into the Sn-rich core, while inhibiting Sn diffusion into the filament pack. Although beneficial as a membrane, the growth of this layer must be controlled as it ultimately decomposes to a disconnected A15 phase. Extensive quantitative image analysis has allowed us to show the relationship between heat treatment temperature and time, the net Cu inward diffusion and the Nausite ring thickness, allowing us to develop optimized low temperature heat treatments that balance the amount of low melting point Cu-Sn with the amount of Sn and Nb lost to Nausite formation. We show that this new heat treatment strategy can significantly increase the Jc of RRP® strands, especially for small diameter sub-elements.
For cost-effective 15-16 T accelerator magnets, the critical current density Jc(15T,4.2K) of commercial Nb3Sn composite wires has to be pushed from the present state-of-the-art for RRP® wires of ~1,650 A/mm2 to ~2,000 A/mm2. Only so much improvement can be obtained through heat treatment optimization. Wire development was therefore carried out in collaboration with Oxford Instruments - Superconducting Technology (OST), which produced three R&D billets to optimize design and layout parameters of their trademarked RRP® process. These wires were studied and characterized virgin and deformed to at a number of sizes through flat-rolling process. The virgin OST 169-restack conductor within this study had an average Jc(4.2K, 16T) ~ 1,300 A/mm2 and its cost was ~$1,700/kg. This was obtained with a Nb to Sn ratio of 3.4:1, which corresponds to ~53%at. Nb, which is presently the achievable upper limit for Nb content in a wire. Results indicate that the Jc of Nb3Sn wires has plateaued. It is clear that to achieve the cost reduction required in magnets for a Hadron Collider, the target increase in Jc can only be achieved by disruptive progress, and that for this reason it is now necessary to invest in research aimed at improving the inherent flux pinning of Nb3Sn.
Prior to his passing in late 2016, Leszek Motowidlo
developed a method of applying the Nb-1Zr/SnO2 internal oxidation method
to APC Nb3Sn through a powder-in-tube (PIT) approach that used low-cost
Cu5Sn4 powder as the Sn source. Two designs of
multifilamentary PIT wire were successfully produced and fine-grain A15 layers
with average grain diameters as small as 30 nm were obtained. High
resolution field emission SEM also indicated the presence of point pinning
sites, particularly at grain boundaries. Magnetization and transport critical
current tests showed a shift in the peak of the pinning force curve toward
higher magnetic field. Deconvolution of the pinning force curves indicated a
strong point pinning component, perhaps produced by the ZrO2
precipitates. It was found that the degree of microstructural refinement was very
sensitive to the volume percent of SnO2 in the core. This
presentation will also look at some limitations of this technique, which
included a strong gradient in grain size, uneven distributions of point-pinning
sites and relatively low levels of conversion of Nb6Sn5
to Nb3Sn. Such compromises will need to be addressed to make this
approach competitive with more fully developed conventional internal Sn and PIT
Nb3Sn wires.
Support
The work is funded by the High Energy Physics division of
the US Department of Energy under a Phase I SBIR award DE-SC0009605. A portion
of this work was performed at the National High Magnetic Field Laboratory,
which is supported by National Science Foundation Cooperative Agreement No.
DMR-1157490 and the State of Florida.
The relatively low cost of multifilamentary Nb$_3$Sn strand compared to HTS alternatives makes it highly valuable to magnet builders to improve the critical current densities (J$_c$) beyond the current production limits of ~ 3 kA/mm$^2$ (12 T,4.2 K) available today. Future applications such as the proposed Future Circular Collider demand increased J$_c$ at higher fields (≥16 T) that current heat treatments have not been optimized for. The two commercially developed high J$_c$ Nb$_3$Sn strands, Powder In Tube (PIT) method, and Rod Restack Process, can be improved primarily in four ways; increase the fine-grain A15 area, increase T$_c$ and H$_{c2}$ homogeneity within the A15 volume, reduce A15 grain size to increase grain boundary pinning density, or introduce point pinning which favorably shifts the maximum pinning force to higher fields. Ideally, any method which accomplishes this should be utilized within the existing manufacturing processes to prevent long or costly R&D projects or impacting yield. Thus optimizing the heat treatment to reduce grain size, while increasing the volume of fine-grain A15 and increasing the H$_{c2}$ homogeneity would be the most desirable route, however, higher temperature heat treatments that better favor H$_{c2}$ also increase the grain size and thus the benefit of improving H$_{c2}$ is offset by fewer pinning sites. In conventional PIT strands, however, 30% of the superconducting A15 phase volume is large-grain (LG) A15, which does not contribute to transport current, and converting this volume to fine grain A15 would be highly beneficial. The LG A15 has proven historically difficult to avoid or control, however, in the past 5 years we have been able to identify the origin of the LG A15 morphology in PIT wires and have demonstrated heat treatments that control its nucleation and growth. Here we summarize our progress in improving the high field J$_c$ of Nb$_3$Sn PIT conductors.
For a list of Exhibitors, please visit: http://www.cec-icmc.org/exhibit/exhibitors/.
The drive for a greener grid is seeing baseload power generation increasingly displaced by intermittent renewables, forcing a change in how grid operators manage their networks. Energy Storage is a key component of the strategy to maintain a stable and reliable supply of electricity, shifting "wrong-time" energy and providing ancillary services from clean sources.
The bulk storage of energy represents a particular challenge. Even with recent cost reductions in battery technologies their costs are high, and the incumbent technologies used for large-scale storage are constrained by geographical requirements.
Liquid Air Energy Storage is based on components proven through decades of use in the Industrial Gas, Oil & Gas and Power Generation sectors and provides a low-cost solution for bulk-scale storage that is ready to be deployed today and can be located where the value is greatest.
Lightweight engineering polymers and additive manufacturing have enabled development of a new cryogenic liquid storage paradigm. State of the art cryogenic storage dewars typically conform to a vacuum jacketed thin wall stainless steel vessel with multi-layer insulation design. While resulting in low boil-off rates, the specific energy is often insufficient for use in weight sensitive aerospace applications. Using 3D printed polymers can increase the specific energy of the tank system by reducing the mass of structural components while matching the boil-off rate to that of the nominal flow demand from a fuel cell. This study investigates the performance of vapor cooled shielding using boil off vapors in a 3D printed polymer liquid hydrogen storage tank using experimental data from a prototype tank. COMSOL computational fluid dynamics is used to model the transient thermal performance during a liquid hydrogen fill and steady state boil-off with liquid nitrogen and liquid hydrogen. Steady state liquid nitrogen boil-off was modeled assuming half the surface area was cooled with vapor through natural convection, with the remaining surface area modeled by liquid natural convection or nucleate boiling. Empirical liquid nitrogen boil-off data was derived from measuring the change in tank mass over time which was 4% greater than modeled performance.
Cryogenic permeation of helium and hydrogen is important for the development of light-weight insulation systems. In this work, we utilized a custom membrane support structure to measure helium and hydrogen permeation rates with a calibrated Adixen Graph D+ variable mass leak detector. Preliminary steady-state and thermal-transient tests of cryogenic helium and hydrogen permeating through 1 mil polyethylene terephthalate (PET) have been conducted between 30 – 90 K. Initial results confirm early experimental efforts that cryogenic permeation strongly deviates from classical Arrhenius-based diffusion. Transient tests conducted with PET and helium have also been conducted between 30 – 300 K, and confirm that permeability begins to deviate from the Arrhenius relation at 150 K.
The Cryogenic Current Comparator (CCC) and its purpose built cryostat were installed in the low-energy Antiproton Decelerator (AD) at CERN in 2015. A pulse-tube cryocooler recondenses evaporated helium to liquid at 4.25 K filling the inner vessel of the cryostat at an equivalent cooling power of 0.55 W. To reduce the transmission of vibration to the highly sensitive CCC the titanium support systems of the cryostat were optimised to be as stiff as possible while limiting the transmission of heat to the liquid helium vessel.
During operation the liquid helium level in the cryostat was seen to reduce, indicating that heat load was higher than intended. To verify the reason for this additional heat load and improve the cryogenic performance of the cryostat an upgrade was undertaken during the 2016 technical stop of the AD.
This article presents the studies undertaken to understand the thermal performance of the cryostat and details the improvements made to reduce heat conduction, techniques employed to reduce transmission of thermal radiation, and procedures used to reduce the diffusion of helium to the vacuum space through ceramic isolators. Finally the upgraded cryogenic performance of the cryostat is presented.
In this paper, a thermal switch used in an integrated cooler system, which consists of a single stage pulse tube refrigerator integrated with a small amount of a phase change material, will be introduced. During the heat load operation, the phase change unit absorbs heat loads by melting a substance in a constant pressure-temperature-volume process, meanwhile, the refrigerator is stopped to avoid vibrations and the thermal switch automatically turns off to reduce the heat leakage between the refrigerator and the phase change unit. Once the substance has been completely melted, the refrigerator begins to work and the thermal switch automatically turns on to reduce the thermal resistance and then the phase change material can refreeze.
The working principle, structure and material selection criteria of the thermal switch will be described in detail in this paper. In addition, the corresponding experimental device was set up and the performance of the thermal switch has been tested. At present, the measured temperature difference between the cold end and the warm head of the thermal switch is less than 0.2 K. The tested “on” and the “off” resistance ratio is 2245, and the “on” resistance and the “off” resistance is 0.224 K/W and 503 K/W, respectively. The heat loss of the test thermal switch is 137.5 mW, while without the thermal switch, the leakage heat is 549.9 mW.
Boil-off calorimetric measurements of Multilayer Insulation (MLI) performances between 4.2 K and shield temperatures varying between 20 K and 60 K are in preparation at CERN for an extensive characterization of MLI blankets of the LHC type. These tests will extend the performance measurements of the blankets to thermal shield temperatures lower than nominal as well as providing performance data for MLI systems with thermal shields operated at lower temperatures as is being proposed for new large accelerators like the Future Circular Collider (FCC). Tests will also cover MLI with different number of layers and layer densities and measure the performance in degraded vacuum. The vertical test cryostat in use has been formerly developed by Wroclaw University of Technology, and consists of an inner liquid Helium tank surrounded by a liquid Nitrogen vessel. In order to have a thermal shield at variable temperatures, an aluminium screen has been designed to be inserted between the two vessels and in thermal contact through a weak link with the guard LHe chamber, thus ensuring a lowest temperature of 20 K. Higher temperatures are obtained by electrical heating of the shield. This paper presents the design of the cryostat and the first qualification tests of the system. The experimental campaign will also be outlined.
Long duration storage of cryogenic fluids is an essential requirement for space missions. Thermal optimization of the storage system is a key objective of the design process to minimize environmental heat leak. The objective of this research is to focus on the thermal optimization of the vapor cooled shield (VCS) in cryogenic liquid storage. Two types of the vapor cooled shield have been studied: those that use the boil-off gasses from the cryogen and those that require additional fluid mass to compensate for the boil-off losses. The effects of the VCS positon, the VCS temperature, the VCS flow rate on the insulation performance on the insulation performance will be simulated and analyzed. An insulation performance testing device has also been designed, built and tested. The simulation results, together with the typical test results of VCS, will be presented in this paper.
Abstract：In the start-stop phase, the foil in the gas foil bearing and the shaft are in a dry friction state. The solid lubricating coating on the foil and rotor has a crucial effect on bearing‘s using life. The friction and wear characteristics of several coating materials， like molybdenum disulfide, aluminum oxide, dense Cr, polyamide，were tested on the friction and wear test rig. The parameters（the bonding strength of the coating and the base material, surface roughness, friction coefficient，etc.） were measured to analyze the effect of the different friction pairs and the preparation process of coating. In this paper, the test materials were also tested on the turbine start-stop test rig.
Keywords：gas foil bearing； tribological properties； start-stop performance； solid lubricant coating
coating
The numerical simulation included solid blades with four different leading-edge thicknesses and four different leading-edge geometries. One of the geometries was square, one was ellipse a(ellipse ratio is 1), one was ellipse b(ellipse ratio is 2), and the other was ellipse c(ellipse ratio is 3). The four thicknesses were 0.7mm, 0.6mm, 0.5mm, 0.4mm. The results show increased efficiency loss for increased leading-edge thickness for square geometry. For ellipse geometries, there was no significant difference when the leading-edge thickness changed at the positive incidence range. For the same leading-edge thickness(0.7mm), square leading-edge caused more loss than ellipse leading-edge. For square geometry, the optimal incidence angle was about -8 degree(0.7mm). For ellipse geometries, the optimal incidence angle was about -30 degree(0.7mm). And with the decrease of leading-edge thickness, the square's optimal incidence angle was toward to zero degree, the ellipse's optimal incidence angle was toward to larger negative angle.
An extensive experimental program has been carried out on a 22 mm tip diameter radial-axial flow cryogenic turboexpander, in order to directly compare performance characteristics by varying the vaneless space. A reference nozzle with radial clearance 0.5 mm was used in the refrigeration system, and seven other nozzles were designed with radial clearance of 0.1 mm, 0.2 mm, 0.8 mm, 1.0 mm, 1.2mm , 1.5 mm and 2mm. As part of the design process a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each design. In this way the variations in the stage efficiency could be attributed to the different vaneless space only, thus allowing direct comparisons to be made. Interstage measurements were taken to capture the static pressure distribution at the rotor inlet and these measurements were then used to validate subsequent numerical models. The overall losses for different stators have been quantified and the variations in the measured and computed efficiency were used to recommend optimum values of the ratio of the nozzle vane trailing edge radius to the rotor leading edge radius (Rte/rle).
Turbo-expander is the core machinery of the helium refrigerator. Bearing as the supporting element is the core technology to impact the design of turbo-expander. The perfect design and performance study for the gas bearing are the premise to ensure the stability of turbo-expander. In this paper, numerical simulation is used to analyze the performance of gas bearing for a 500W helium refrigerator turbine, and the optimization design of the gas bearing has been completed. And the gas bearing structure parameters have a guiding role in the processing technology. Finally, the turbine experiments verify that the gas bearing has good performance, and ensure the stable operation of the turbine.
Most modern medium and large capacity helium liquefaction/refrigeration plants employ high speed cryogenic turboexpanders in their refrigeration/liquefaction cycles as active cooling devices. The operating speed of these turboexpanders is in the range of 3000-5000 Hz and hence specialized types of bearings are required. Floating pad journal bearing, which is a special type of tilting pad journal bearing where mechanical pivots are absent and pads are fully suspended in gas, can be a good solution for stable operation of these high speed compact rotors. The reference to the use of such bearings for cryogenic applications, using process fluid as bearing gas to eliminate contamination, can be found in literature. This type of bearing is a combination of aerodynamic and aerostatic bearing in which both the actions are interdependent. The pads are separated from shaft as well as from housing by fluid film between them, and both these sides of pad are interconnected by a network of feed holes. In the present work, the aim is to characterize floating pad journal bearings through parametric studies. The steady state performance characteristics of the bearing are represented by load capacity and static stiffness coefficients of the bearing. The geometrical parameters such as bearing clearances, preload of pads, etc. are varied and performance characteristics of the floating pad journal bearing are studied and presented. The dependence of stiffness coefficients on operating pressure and rotational speed of shaft is also analyzed. Finite element formulation of Reynolds equation is used for computation of pressure profiles on the bearing area. A brief description of numerical model and solution technique used for analysis of the bearing is also discussed in this paper.
Coal-bed methane (CBM) reserves are rich in Sinkiang of China, and liquefaction is a critical step for the CBM exploration and utilization. Different from other CBM gas fields in China, CBM distribution in Sinkiang is widespread but scattered, and the pressure, flow-rate and nitrogen content of CBM feed vary significantly. The skid-mounted liquefaction device is suggested as an efficient and economical way to recover methane. Turbo-expander is one of the most important parts which generates the cooling capacity for the cryogenic liquefaction system. Using the two-phase turbo-expander, more cooling capacity and higher liquefied fraction can be achieved. In this study, two skid-mounted CBM liquefaction processes are analyzed: one process is based on the direct expansion of feed gas and another process is based on nitrogen expansion cooling cycle. Cryogenic two-phase turbo-expander is employed to improve the efficiency of CBM liquefaction process. The unit liquefaction power consumption for CBM feed gas is used as the object function for process optimization, and optimum parameters of the two liquefaction processes with different pressure, flow-rate and nitrogen content are obtained. Based on the optimal results, the off-design performance in a wide operation range and the effects on liquefaction performance of two-phase turbo-expander are investigated.
Modern infrared imagers often rely on split Stirling linear cryocoolers comprising compressor and expander units interconnected by the configurable transfer line. The relative position of the cryocooler components is governed by the optical design along with packaging constraints.
Vibration export produced by such a cryocooler is a pair of tonal and coherent forces. The resulting angular and translational vibration may produce excessive line of sight jitter and defocusing affecting imaging performance in the long range and high resolution infrared imagers.
Since linear cryocooler is usually driven at a fixed and precisely adjustable frequency, a tuned dynamic absorber is ideally suited and cost effective tool for attenuation the cooler induced vibration and improving optical performance. As different from the traditional unimodal concept, the authors are considering multimodal tuned dynamic absorber made in the form of weakly damped mechanical resonator, where the frequencies of useful dynamic modes are essentially tuned to the driving frequency. Dynamic analysis and experimental testing show that the dynamic reactions (forces and moments) produced by such a device may simultaneously attenuate both translational and angular components of cryocooler-induced vibration, thus improving the imagery quality. The authors are considering different embodiments and their suitability for different packaging concepts. The outcomes of theoretical predictions are supported by full scale experimentation.
Sorption compressor is the most critical component in a sorption-based cooler that is appealing to many applications because of its plausible feature of vibration-free. To design a sorption compressor, it is essential to understand the thermal and hydraulic behaviors within the sorption cells. In this paper, based on a dynamic model developed previously, the detailed heat and mass transfer in the sorption-compressor cell has been numerically simulated. The simulated results reveal the inhomogeneous desorption/adsorption phenomenon due to the temperature and pressure distribution within the sorbent during a sorption-cycling period. The analysis is useful to help further optimizing the cell configuration to improve the performance and reduce the size.
Contamination gas is one of the four key factors degrading the long life of pulse tube cryocooler. In this paper, in order to optimize the contamination control measure and improve the life of cryocooler, the transmission of contamination gas had been deeply studied. The fluent software was used to simulate the diffusion of contamination gas among piston clearance, intermediate connecting pipe and regenerator. Mass flow of contamination gas and gas partial pressure in the regenerator were calculated. It would provide support for mechanism of contamination gas condensation and studying regenerator failure.
JT compressor is one of the Key components in space 4K JT cryocooler. The oil-free linear compressor becomes issue of the space JT compressor research because of its high reliability, high efficiency, long life and simple structure.
In this paper, the linear JT compressor developed by our laboratory is experimentally studied for the purpose of improving its pressure ratio. The stiffness of the plate spring is optimized. Besides, the influence of charge pressure, input power and operating frequency are tested to find out its optimum working condition. And the stroke of the piston is measured to evaluate the performance of the JT compressor. Eventually, pressure ratio of the JT compressor increases from 7.5 to 12 in two-stage compression. And pressure ratio of 17.6 is gained in three-stage compression.
A high efficiency and low vibration stirling cooler has been demonstrated for cooling down the sensitive IR devices. A high efficiency compressor implementing the technology of dual opposed moving magnet and flexure bearing has been optimized to drive pneumatically a stirling cold finger also implementing flexure bearing technology. Through theoretical study and experimental study on the spring stiffness and the stroke of the displacer, the cooler could reach performance of 3W/80K under 60 W of electrical power.
It is also particular important that the suppression of the vibrations coming from the compressor and the stirling cold finger. The vibration of the compressor was caused by the unbalance force between dual opposed structures. It was suppressed by reducing the weight of moving-mass and controlling the process of assembling. The vibration suppression of the stirling cold finger was implemented in terms of a mass-spring passive balancer. The vibration of compressor and the stirling cold finger could decreased to 10mg and 5mg respectively under the above solutions.
One of the most important characteristics of spaceborne stirling cryocooler is its reliability over a lifetime. The wear abrasion and gas contamination existing in stirling cryocooler are the most failure modes that influence the reliability of spaceborne stirling cryocooler. While design improvements have reduced the probability of the wear abrasion, the excessive gas contamination is still a major risk, typically in excess of 10 years.
Aimed at gas contamination failure mode in stirling cooler, experiments were realized in order to study the effect of contamination on the working gas of stirling cryocooler operating at 80 K. The accelerated contamination experiments were performed to quantify the effect of impurity gas. The curve of the outgassing rate as a function of the time in the stirling cooler was obtained and discussed. The results supported the reliabilty design and test of stirling cooler.
Investigating cooling cycles operating with gas mixtures require the ability to evaluate the thermodynamic properties of mixtures, usually as a function of temperature, pressure, and composition. Working with mixed refrigerants for Joule-Thomson (JT) cryocoolers, it is desired to calculate the enthalpy of mixtures for determining their specific cooling power. Evaluating the mixture enthalpies is essential at the earliest stage of the research, in order to determine the mixture composition. Most researchers use available data bases for determining the properties of mixtures; however, it appears that data base results are often limited by temperatures, pressures, and components.
In this paper an analytical method for calculating the enthalpy of mixtures is presented. The method consists of equation of state calculations, and the results are compared with the enthalpies provided by REFPROP™ data base. This method is implemented in our research procedure for developing mixed refrigerant JT cryocoolers.
Cryogenic adsorber is essential in large cryogenic engineering system due to the high quality gas demand, the design of the adsorber requires accurate adsorption data. A cryosorption setup has been built to investigate the cryogenic adsorption of helium and nitrogen on commercial PICA activated carbon, molecular simulation of helium and nitrogen on activated carbon is also studied based on amorphous carbon model. Combined with the cryosorption data, a revisit to the design of a 80K cryogenic adsorber is also included, it helps in the lateral design of the cryogenic adsorber in large cryogenic engineering.
For decades NASA has used helium to pressurize liquid hydrogen propellant tanks to maintain tank pressure and reduce boil-off. This process causes helium gas to dissolve into liquid hydrogen creating a cryogenic mixture with thermodynamic properties that vary from pure liquid hydrogen. Traditional NASA models have been unable to account for this dissolved helium due to a lack of fundamental property information. Recent measurements of parahydrogen-helium mixtures enabled the development of the first multi-phase EOS for parahydrogen-helium mixtures. This new EOS has been implemented into NASA’s Generalized Fluid System Simulation Program (GFSSP) to determine the significance of mixture non-idealities. A model was developed for a simple self-pressurization of a liquid hydrogen propellant tank due to boil-off. The model was run assuming that the liquid propellant was pure liquid hydrogen and then assuming helium dissolved into the liquid using the new helium-hydrogen EOS. The analysis shows that having dissolved helium in the propellant does not have a significant effect on the tank pressurization rate but does affect the rate at which the propellant temperature rises.
Numerical study of cryogenic gas dispersion benefits for the risk reduction of leakage of hazard cryogenic gases. Up to now, phase change physics of small quantity of water involved in the cryogenic gas has not been considered in numerical modeling of the dynamic dispersion behaviors of cryogenic gas in the atmosphere. The present study develops a computational fluid dynamic (CFD) model considering water phase change to simulate the atmospheric cloud flow resulting from the cryogenic gas leakage. Numerical simulation of liquefied natural gas (LNG) dispersion was performed, in which two-phase flow was modeled based on the single-fluid mixture model, and the species dispersion of natural gas, water vapor, oxygen and nitrogen in the atmosphere were calculated based on the respective convective-diffusion conservation equations. The original Hertz-Knudsen relation was modified to determine the mass transfer between the water vapor and the droplet, in which, the sensitivity of condensation and evaporation coefficients on simulating results were examined. The results of the calculation were compared with the counterparts without accounting for the phase change, the experimental data from Burro and Coyote trials and the simulation results with software SLAB and FEM3. The comparisons validate the improvements of the present two-phase modeling approach. Simulations and analysis of nitrogen gas dispersion were also presented.
The SUPRAPOWER consortium, an EU FP7 funded research project, is developing an innovative 10 MW class superconducting generator (SCG) to provide an important breakthrough in the offshore wind industry. It is a partial SCG with MgB2 wires used in the field coils while conventional copper conductors are used in the armature coils. Due to the requirements of handling, maintenance, reliability of long-term offshore operation, the cooling system of SUPRAPOWER SCG adopts a modular and cryogen-free design. The SCG contains 48 identical superconducting coils and each coil is enveloped in one of the 48 identical modular cryostats.
Benefiting from the modular concept, the key challenges of such innovative 10 MW SCG e.g. the modular superconducting (SC) coil and associated cryogenic systems could be validated through a scale-down experiment. This validator consists of two modular SC coils rotating together with the iron poles and yoke to generate the magnetic field. The modular cryostat enveloping the coil consists of a vacuum vessel, an active cooled thermal shield with multi-layer insulation and corresponding supporting structures. In order to achieve the SC coils working temperature of 20 K, a two-stage G-M cryocooler will be installed and linked to the two modular cryostats by means of conductive copper connection. A non-modular cryostat was developed to envelop the cold head of the cryocooler, the thermal link, and three binary current leads to feed electrically the coils while keeping the heat load from ambient as low as possible. A rotary union with Ferrofluid sealing was developed to transfer the helium gas between the rotating cold head and stationary oil-lubricated compressor. In this paper, the design and manufacturing of each component will be described, and the assembly and some preliminary experimental test of the cryogenic cooling system for the validator will be also presented.
The SUPRAPOWER, an EU FP7 funded research project, are developing an innovative 10 MW class superconducting generator (SCG) to provide an important breakthrough in offshore wind industrial solutions. It is a partial SCG with MgB2 wires used in the field coils while copper wires at ambient temperature are implemented in the armature coils. The cryogenic cooling system of SUPRAPOWER SCG adopts a cryogen-free design in view of the handling, maintenance, and reliability of long-term offshore operation, that is, the superconducting coils are cooled down to working temperatures with regenerative cryocoolers by means of conduction.
By evaluating the availability and required cooling capacity in the temperatures range around 20 K, we finally selected a Gifford-McMahon (GM) cryocooler among all the candidates since GM cryocoolers are becoming readily available from many manufacturers at relatively low cost and service periods of one or two years. The cold head of GM cryocooler will be directly attached or linked to the rotating superconducting coil. Hence, the cold head is supposed to rotate together with the rotor. However, the compressor of GM cryocooler is sensitive to pitch, and must not be kept beyond 5 degrees, not to mention rotating conditions since it normally utilizes oil lubricated Helium scroll compressor which is well commercialized and extensively used in the refrigeration industry. As a consequence, a rotary union (RU) utilizing Ferrofluidic® sealing technology was developed to transfer helium gas between the rotating cold head and stationary helium compressor at ambient temperatures. It contains a high-pressure and low-pressure helium path with multiple ports, respectively. Besides the helium path, slip rings with optical fiber channels are also integrated into this RU to transfer current and measurement signals. In this paper, the design, manufacturing and preliminary test of the RU will be conducted.
Many cryogenic systems around the world for cost, preventative damage, safety or other reasons are concerned with the sudden catastrophic loss of vacuum.
The experiments in this paper were designed to simulate the sudden vacuum break in the beam-line pipe of a liquid helium cooled superconducting particle accelerator. This paper expands previous research conducted at the NHMFL and looks at the differences between normal helium (He I) and superfluid helium (He II). For the experiment, a straight pipe was evacuated and immersed in liquid helium at 4.2K and 2 K. Vacuum loss was simulated by opening a solenoid valve on a buffer tank filled with 760 Torr nitrogen gas. The nitrogen passed through a venture tube so the mass flow rate could be metered. Temperature was monitored along the tube at regular intervals and a measured temperature rise indicated the arrival of the gas front.
Our preliminary results suggested that the speed of the gas front through the experiment decreased exponentially along the tube for both normal liquid helium and super-fluid helium. Furthermore, the decay of the gas front speed does not show obvious difference between the two distinct helium phases despite the difference in helium heat transfer mechanisms: convection vs thermal counterflow. More systematic measurements are planned in a helical tube system to further verify the results.
Keywords: Air Propagation, Loss of vacuum, Superfluid helium, Particle accelerator
Cryogenic energy storage (CES) systems are promising alternative to existing electrical energy storage technologies such as a pumped hydroelectric storage (PHS) or compressed air energy storage (CAES). In CES systems the electrical energy is used to liquefy a cryogenic fluid. The liquid can be stored in large cryogenic tanks for a long time. When a demand for the electricity is high the liquid cryogen is pumped to high pressure and then warmed in a heat exchanger using ambient temperature or an available waste heat source. The vaporized cryogen is then used to drive a turbine and generate the electricity. Most research on the cryogenic energy storage focuses on the liquid air energy storage, as atmospheric air is widely available and therefore it does not limit a location of the energy storage plant. Nevertheless, the CES with other gases as the working fluids can exhibit a higher efficiency. In this research a performance analysis of simple CES systems with several working fluids was performed.
Production of LNG with an Active Magnetic Regenerative Liquefier
By Corey Archipley1, John Barclay1, Jamie Holladay2, Kerry Meinhardt2, Evgueni Polikarpov2, and Edwin Thomsen2
1 Emerald Energy NW, LLC. (EENW); 2 Pacific Northwest National Laboratory (PNNL). The support of this work by the U.S. DOE/EERE/FCTO is appreciated.
The figure of merit (FOM) of a liquefier is the ratio of ideal to real specific work required to liquefy a unit mass of gas. Because liquid cryogens are excellent for storage, transport, and delivery of industrial gases and cryofuels like LNG and LH2, conventional gas-cycle liquefier technology has been well developed with a maximum FOM of ~0.35. Demonstration of regenerative magnetic cycles near room temperature in 1976 and invention of the active magnetic regenerator in 1982 identified the potential of magnetic liquefaction technology for higher FOMs. We have designed an efficient active magnetic regenerative liquefier (AMRL) to liquefy ~1000 gallons/day of LNG at 123 K using 200 psia natural gas feedstock at 280 K. Eight stages with different magnetic refrigerants with large magnetocaloric effects near the average hot temperature of each stage were selected. A numerical model was used to calculate thermodynamic performance as a function of key design choices. The 1-D transient model updates pressure, temperature, flow, magnetic-field dependent properties of magnetic refrigerants and helium heat transfer gas each microsecond time step. It uses a finite difference Eulerian technique to solve five coupled non-homogeneous partial differential equations that describe operation of each AMRR stage in the AMRL. The model tracks each regenerator vs time through the four AMR cycle steps: hot-to-cold flow in demagnetized regenerators; no flow during magnetic field changes; cold-to-hot flow in magnetized regenerators and no flow during opposite magnetic field changes. The design performance, size, cost, and FOM of this LNG liquefier are presented and discussed in this paper.
Due to the nature of fluctuation and intermittency, the utilization of wind and solar power will bring a huge impact to the power grid management. Therefore a novel hybrid wind-solar-liquid air energy storage (WS-LAES) system was proposed to solve the problems. In this system, wind and solar power are stored in the forms of liquid air by cryogenic liquefaction technology and thermal energy by solar collector, respectively. Owing to the high density of liquid air, the system has a large storage capacity and no geographic constraints. The WS-LAES system can store unstable wind and solar power for a stable output of electric energy and hot water.Combined with organic Rankin cycle (ORC), the energy cascade utilization was also achieved. Moreover, the thermodynamic analysis was carried out to investigate the best system performance. The result shows that the increase of ambient temperature has a negative effect on the system performance, while the increase of turbine inlet temperature has a positive effect.
Analytical and numerical investigations of a Heisenberg Vortex Tube (HVT) are performed to estimate the cooling potential with cryogenic hydrogen. The Ranque-Hilsch Vortex Tube (RHVT) is a device that tangentially injects a compressed fluid stream into a cylindrical geometry to promote temperature separation between inner and outer flows. The HVT is the result of lining the inside of a RHVT with a hydrogen catalyst. This is the first concept to utilize the endothermic heat of para-orthohydrogen conversion to aid primary cooling. A review of 1st order vortex tube models available in the literature is presented and adapted to accommodate cryogenic hydrogen properties. These first order model predictions are compared with Computational Fluid Dynamics (CFD) simulations.
Small, modular, efficient hydrogen liquefiers are needed to expand use of hydrogen as an energy currency. The Heisenberg Vortex Tube (HVT) is a novel cooling concept based on the Ranque-Hilsch Vortex Tube (RHVT) with a catalytic liner – the first concept to reverse the exothermic ortho-parahydrogen conversion to directly aid primary hydrogen cooling. Analysis of the design parameters of the HVT and experiment are presented. Initial experimental measurements are presented of the efficiency gains by the HVT concept over traditional RHVT.
A hybrid magnet which includes a water-cooled magenet and a superconducting magnet has been developed at the High Magnetic Field Laboratory of the Chinese Academy of Sciences. The superconducting coils which are made of Nb3Sn cable-in-conduit conductor (CICC) are forced-flow cooled by 4.5 K supercritical helium. In this paper, a mathematical method is proposed to simulate the pressure, temperature and mass flow rate distribution of each coil in the process of cooldown from room temperature to 4.5 K with maximum temperature differences of 50 K. The experimental results show that it takes 24 days to cool down all the superconducting coils to 4.5 K and the characteristics of the supercritical helium in CICCs are measured. As a conclusion, the functions of the input temperature for the cooldown, the distributions of mass flow rates in each coil are summarized, and the friction factor, as well as heat transfer coefficient in each CICC channel is calculated and the related former empirical formula has been revised.
In order to improve the stability of the superconducting magnets, e.g. MRI magnets, the NbTi superconducting wires were used to wind magnets without electrical insulation layers. The magnets were made with different induction values. As comparisons, the same kind of wires with insulation layers were used to wind magnets of similar induction values. The magnets were tested at 4.2K in a LHe bath. The results were analyzed and theoretically investigated. The results reveal that non-insulation winding is beneficial to magnet stability, however, the long charging and discharging period make it unacceptable for the technique to be put into practical applications.
This article mainly introduces the treatment of the internal leakage of the helium liquefier. The Linde L70 helium liquefier I run was found to be difficult to maintain the vacuum, the system is difficult to carry out. Gradual investigation of the problem, that is cold box internal pipeline leakage. Then I and my colleagues in the Linde company's proposal to develop a maintenance plan, the first pipeline separation, and then split the cold box, leak detection, welding repair. Because the leak is very small, leak detection takes a lot of time, try a variety of leak detection methods, and ultimately find the leak and repair successfully. After the repair, helium liquefier works well so far.The maintenance was carried out at the location of the plant, to avoid the cold box sent back to the original factory testing and maintenance. It is hoped that these experiences will help the helium liquefier users in a similar situation.
In this paper, a 500W@4.5K helium refrigerator for ADS (Accelerator Driven Subcritical) project of CAS (Chinese Academy of Sciences) has been designed and constructed. The function requirements and process analysis of this helium refrigerator are described. Based on the floating pressure cycle, the balanced design between the refrigerator and its liquefier for an equal Carnot work with the same high efficiencies is presented. The constraints of components and operation strategies in refrigeration mode and liquefaction mode are discussed. Commissioning results indicate that this 500W/4.5K helium refrigerator can provide 5.17g/s (or 150L/h) LHe in liquefaction mode or 500W at 4.5K in refrigeration mode with the FOM (Figure of Merit) of 14%. Exiting problems are analyzed and discussed through comparing the theory calculation, dynamic simulation and experimental data, and some suggestions end this paper.
A new 4.5K cold box at Jefferson Lab (JLab) Cryogenic Test Facility (CTF) was recently installed and commissioned to upgrade the existing 4.5 K refrigeration system and work in parallel with the existing 4.5 K cold box. This new 4.5 K cold box is equipped with two turbo-expanders and, at its maximum capacity condition, can support up to 6.6 g/s of helium liquefaction or 650 W of refrigeration at 4.5 K. It can also handle up to 10 g/s 30 K return flow for 2 K refrigeration recovery that supports cryo-module and superconducting cavity testing. Performances of the cold box at its maximum capacity conditions as well as several other operating modes were tested for acceptance. We will briefly review the new 4.5 K cold box design features and discuss the commissioning and performance testing results.
The Facility for Rare Isotope Beams (FRIB) will be a scientific user facility for the Office of Nuclear Physics in the U.S. Department of Energy Office of Science (DOE-SC). The FRIB LINAC will be comprised of cryomodules each with multiple Superconducting Radio Frequency (SRF) cavities operating at 2 K. A helium refrigeration system was designed, fabricated, installed and commissioned in the SRF high bay building to test and certify these cavities and cryomodules before installation in the FRIB LINAC tunnel. The helium refrigeration system includes a helium refrigerator which has nominal capacity of 900 W at 4 K, 5000 L liquid helium storage dewar, helium gas storage, two room temperature vacuum pumps capable of 2.5 g/s each for 2 K testing, purifier, purifier recovery compressor, and the distribution system for liquid nitrogen and helium. The helium refrigeration system is now operational supporting three below grade cavity testing dewars and one cryomodule testing bunker meeting the required throughput of 1 cavity per day.
The Shanghai Synchrotron Radiation Facility (SSRF) is an intermediate energy light source built at Zhang-Jiang Hi-Tech Park in Shanghai, China. The SSRF consists of a 432 m circumference storage ring with operating energy of 3.5 GeV and minimum emittance of 2.9 nm-rad, a full energy booster, a 150 MeV electron Linac. The RF power and voltage required for storing the electron beam are provided by means of three SC cryomodules, each containing one 499.654MHz superconducting cavity. The cavities, made of Niobium, are bath-cooled with saturated liquid helium at 4.5 K. A cryogenic plant with cooling capacity of 650 W at 4.5 K has been in operation since August of 2008 to provide cooling for the three superconducting cavities.
In order to further improve the performance of SSRF, the following SC devices will be applied as the SSRF Phase II project:
1) One third harmonic SRF cavity with 1.5 GHz，to be positioned at the SSRF storage ring, will run at 2 K (31 mbar) by bath cooling.
2) One superconducting wiggler is to be used for one of the new-built beam lines, ultra-hard multi-functional beam line. The SC wiggler will be cooled by cryocoolers at 4.2 K region by bath cooling.
For the purpose of supporting operation of the above SC devices, a new cryogenic system ( SSRF-II cryoplant) with equivalent cooling capacity of at least 650 W at 4.5 K (including at least 60 W at 2 K) will be designed, fabricated, test and operated for the SSRF-II.
Additionally, the new cryoplant will be used as the back-up of current 650 W refrigeration system at 4.5 K to support normal operation of the online three 500MHz SRF cavities in case of any failure occurred to the current 4.5 K cryoplant.
This paper will present the whole plan of SSRF-II cryoplant.
Based on the traditional heat exchanger design method, the sub-atmospheric plate-fin heat exchanger in superfluid helium refrigeration system is designed by calculating with distributed parameter differential element method. This enables to obtain the geometry，temperature distribution and the pressure drop inside the heat exchanger. So that the optimal solution can be selected after comparing a series of calculation and experimental results. Such method can provide a reference for the design and further exploration of sub-atmospheric heat exchangers.
Wall-type heat exchanger(WTHX) and Fin-type heat exchanger(FTHX) are attached to the first and second stage cold head of two G-M crycoolers respectively in the simulating experimental platform of the internal purifier(SEPEIP). WTHX and FTHX play a significant role in SEPEIP, WTHX is designed to remove heat from helium and freeze-out extremely few impurities, FTHX is for further cooling the helium. In this study, numerical simulation and experimental results for WTHX and FTHX are carried out. According to the comparison, Numerical results are well consistent with the theoretical results. It is presented the better performance of the WTHX and FTHX..
Both numerical and analytical models are developed to characterize the heat and mass transfer processes in a cryogenic CO2, N2 mixture gas de-sublimating within a cross-flow finned duct heat exchanger system. Heat is transferred across the exchanger from the mixture gas to a flow of cold gas (either nitrogen or helium). The approach follows analyses similar to those used to characterize the condensation of water vapor out of a moist-air mixture. The models enable variations in the outlet temperatures of the gas mixture and coolant, the CO2 mole fractions at the outlet, and the temperature distribution and de-sublimating rate of CO2 to be studied as a function of the mixture and coolant flow rates, the inlet mixture composition, and the geometric parameters of the finned heat exchanger.
A computational fluid dynamics (CFD) model with simplified structure and periodic boundary conditions is applied to the shell side of spiral-wound heat exchangers. And a series of numerical investigations on heat transfer and flow characteristics are carried out using this model. The heat transfer coefficients on the bottom of tubes increases first and then decreases with radial angle, because of the influence of the back flow and the axial velocity for inclined tubes. The mean absolute deviation between simulated heat transfer coefficients and measured values for methane, ethane, nitrogen and a mixture (methane/ethane) is within 5% for Reynolds number over 30000. As for the pressure drop, the simulated values are smaller than the measured values and the mean absolute deviation is within 9%. The results of numerical simulation show that the pressure drops and heat transfer coefficients on shell side of spiral-wound heat exchangers decrease with the increase of the winding angle of the tubes. To consider of the winding angle, the modified correlations of Nusselt number and friction factor, and , are proposed.
To design the heat exchanger, whose effectiveness and pressure loss meet the process requirements, by using the minimum volume, the effects of geometric parameters on multi-stream parallel flow pilate-fin heat exchangers’ effectiveness and pressure loss should be studied. Using both numerical and experimental methods, this paper studies these effects. The results obtained in this paper are valuable for the optimum design of multi-stream plate-fin heat exchanger.
With high specific heat and density, supercritical helium can be used to reduce the temperature fluctuation and improve temperature uniformity in the low temperature conditions. However, the natural convection of the supercritical helium has a great influence on the suppression of the temperature oscillation. In this paper, a transient three-dimensional numerical simulation is carried out for the natural convection in the cylinder with aspect ratio of 3 to analyze the effect of natural convection on transferring of temperature fluctuations. According to the results of numerical calculation, a cryogenic system cooled by GM cryocooler is designed to study the influence of natural convection of supercritical helium on temperature fluctuation suppression.
Fully superconducting rotating machines produce the advantages of lightweight, compactness and high efficiency compared with conventional ones. When those are applied to electric propulsion aircrafts, tremendous innovation will be brought about to air transportation. To realize that, it is necessary to reduce the ac loss in superconducting armature windings, also to enhance the current capacity and to develop cooling systems with lightweight and availability of cold heat of liquid fuel such as hydrogen and methane. Our research group has developed these required techniques for REBCO superconducting transformers so far. The ac loss of REBCO superconducting windings was reduced by laser-scribing of a REBCO tape and its special winding. The current capacity of windings was enhanced without increment of ac loss by forming transposed parallel conductors. Turbo-Brayton refrigerators with neon gas as a working fluid were also developed. The compressor and expander both had turbines with a non-contact magnetic bearing. As a result, a 3φ-66kV/6.9kV-2MVA model transformer was successfully built with REBCO superconducting tapes. Currently, we are developing fully superconducting rotating machines applying the developed techniques to field and armature windings under the support of JST. Our first task was the verification of the applicability of ac loss reduction technique for transformer windings to the armature windings. The current sharing properties among the filaments in laser-scribed REBCO tapes wound into the armature winding of a small test motor were investigated during the operation in liquid nitrogen at 77K. The almost even current sharing among the filaments suggested the fact that no shielding current was induced and the ac loss was reduced in proportion to the filament width since the shielding current is a loop current. In addition we are developing superconducting triaxial cables. In this conference we will introduce out recent works in relation to the development of electric propulsion aircrafts.
Synchronous generators employing rotor coils wound from high-Tc superconducting (HTS) wire, are attractive for a range of applications requiring very high torque and power densities. However, the injection of large DC currents into rotating HTS coils presents a technical challenge. In this paper we discuss the development of a new type of brushless exciter for HTS rotors, which is based on a dynamo-type HTS flux pump. This device applies a rotating magnetic field across the cryostat wall which leads to the injection of a DC superconducting current into the rotor coil circuit.
Our approach fundamentally reduces the thermal load upon the cryogenic system by removing the need for thermally inefficient normal-conducting current leads. It also obviates the need for high current slip-rings which can be subject to very high wear rates.
We report results from an experimental laboratory device and show that it behaves as a constant DC voltage source with an effective internal resistance. We then discuss the design of a prototype brushless exciter based on our experimental device, and describe its integration with a demonstration 10 kW HTS generator. We estimate the thermal load presented by our prototype exciter, and show that this can be further minimised by utilising duty cycle operation of the device. In this manner, the steady-state heat load is reduced by more than an order of magnitude below that of equivalently-rated metal current leads.
References:
Interest in fully electric and hybrid electric aircraft is being driven by gains in efficiency, fuel savings, noise and emission reductions and increased flexibility of aircraft and propulsion system design. magniX is developing and prototyping superconducting electric machines with the goal of demonstrating power densities in excess of 25 kW/kg.
Superconducting generators and motors are synonymous with enhanced efficiency, reduced weight and compact size compared to conventional technologies. magniX is building superconducting generators and motors suitable for intense energy and efficiency sensitive applications such as all electric aircraft motors and generators —it is the only known technology capable of satisfying these requirements.
magniX has unique capabilities and proven intellectual property in high power density electric motors suited to aircraft propulsion embodied in our magnifluxTM technology. Our approach overcomes many of the historical issues associated with superconducting machines by eliminating rotating cryogenic joints through the use of a stationary cryostat and non-cryogenic normal conducting rotor. Our novel flux directing coil arrangements maximize the air gap flux density while also eliminating the need for ferromagnetic shielding reducing overall weight significantly. A discussion of the progress of the magniflux alpha prototype design, construction and testing will be presented.
In the short and medium term, permanent magnet machines have a place in the electric aircraft segment. Results of the development and testing of our magni5 permanent magnet motor with a power density of 5kw/kg will be presented along with a discussion on thermal management and the optimization of the electromagnetic design of this class of machine.
In-field current transport property is one of the most important properties of high Tc superconducting tapes for practical applications. Usually the current-voltage (I-V) characteristics or critical current (Ic) are characterized by the four probe transport measurement or magnetization measurement using a short piece sample. In a practical application, however, the piece length of the tape strands reach more than hundreds of meters or km scale. This indicates that the influence of positional variation of Ic should also be taken into account to describe the I-V characteristics in a real device. In fact, the characterization of spatial Ic variation attracts much attention as a quality control of the long length tapes. However, the relationship between the spatial Ic variation and the local- and/or global-I-V characteristics are not well established. In this study, we have succeeded in measuring in-field Ic variation as a function of longitudinal coordinate, x, in reel-to-reel manner under external magnetic fields up to 4 T at 77 K and 65 K, respectively. We also obtained position-dependent I-V characteristics by site specified transport measurements using the same sample. We proposed an analytical model to describe the position-dependent I-V characteristics based on the Ic(x) in the long length tape. It has been shown that the analytical expression shows good agreement with the position-dependent in-field transport measurements. Namely, this approach allows us to describe the I-V characteristics as function of B, T, and x including position dependent n-index and localized flux flow dissipation in the long length tape.
Acknowledgements: This work was supported by “JSPS KAKENHI (16H02334)”.
The AC loss of different HTS cable types were measured in alternating magnetic fields including Conductor On Round Core (CORC) cables, stacked tape conductors and Roebel cable. The applied AC magnetic field is sinusoidal with amplitudes in the range of 5 to 400 mT and frequencies up to 0.1 Hz. The AC loss of CORC and Roebel cable was measured at 4.2 and 77 K. Inter-tape contact resistance measurements showed differences for current sharing between REBCO tapes in HTS cables.
In addition detailed method of stress-strain state modeling in CORC conductors was developed. The model is based on Finite Element Method (FEM) and extensive strain measurements on REBCO tapes. Systematic measurements on single REBCO tapes were carried out combining axial tension and torsion as well as transverse loading. The FE model takes into account temperature dependence and the elastic-plastic properties of the tape materials and includes initial processing conditions during tape manufacture up to magnet operating conditions. Furthermore a comparison of FEM simulations with CORC cable bending experiments is presented with special attention for the critical bending radius as the threshold where the tapes in the CORC become irreversibly degraded. The influence of tape inter-layer friction was also investigated. A brief overview of the results is presented.
A new facility for the measurement of AC loss in superconductors at high dB/dt has been developed, and recently tested and calibrated for operation. The test device has a spinning rotor consisting of permanent magnets arranged in a Halbach array; which exposes samples in a stator position with a peak radial field of 0.57 T, and with high rotation speeds up to 3600 rpm achieves a radial dB/dt is 543 T/s and tangential dB/dt is 249 T/s. Loss is measured by calorimetry using nitrogen boiloff from a double wall calorimeter feeding a gas flow meter, and the system was calibrated using power from a known resistor. For calibration, Cu-tape and YBCO-tape losses were measured and compared to results of a solenoidal magnet AC loss system measurement of the same samples but limited to a field of amplitude 0.1 T and a dB/dt of 100 T/s. Herein the use of this system for measuring AC losses of a variety of YBCO coated conductors and cables will be performed, and results will be compared to measurements with a a solenoid magnet system and theory. Coated conductors are provided by several manufacturers with different architectures including filamented, varying width, and different quench protection metal layers with varying thickness. Also AC losses will be reported on several types of cable structures, including stacked tapes and conductor-on-round-core (CORC) structures.
Acknowledgement: Air Force Office of Scientific Research (AFOSR), U.S. Air Force ResearchLaboratory – Aerospace Systems Directorate (AFRL/RQ)
Measurements were performed on a 40 centimeters length of 27-strand cored (F095) and 27-strand RRP non-cored Nb3Sn Rutherford cable which were mounted onto a U-shaped holder. For the cored cable: the core material was 316 S.S, the core was centered and had a width of 10.8mm, the cable was keystoned with a 0.95 degree angle, and the strands were OST-RRP with a 1.0mm OD and 60 filaments. For the un-cored cable: the cable wasn’t keystoned and the strands were OST-RRP with a 1.0mm OD and 60 filaments. All samples were reacted under 20 MPa and one of each sample was epoxy impregnated using standard magnet protocols. Current was injected into a single strand at varying I/Ic and a heat pulse from a carbon paste heater was used to initiate current sharing. Current-distribution was measured using voltage taps. The ICR for the un-cored cable was less than that of the cored cable and the current sharing was greater for the un-cored cable. These measurements were performed as a screening for cable and cable preparation protocol for larger scale measurements.
A robust detection of spontaneous quenching is essential for protecting superconducting magnets and machinery from thermal damage. In coils of high-temperature superconductors (HTS) slow propagation of the normal zone makes common voltage-based quench detection schemes unreliable. Here, we propose and validate an alternative quench detection technique for HTS conductors based on monitoring their internal temperature with acoustic waves. Periodic pulsed excitation is applied using a piezo-transducer to a conductor or coil under test, and the transient mechanical response is recorded, providing a unique acoustic "fingerprint" of the system. Temperature-induced variations of the Young's modulus of <0.01% can then be readily detected by comparing the transient waveform to its undisturbed reference. We demonstrate by simulations and experiments a capability to resolve a temperature rise of < 1 K in the conductor quenching inside a stack at 77 K, on par with voltage detection at 1 microvolt/cm. Acoustic quench detection in a single 120 cm-long HTS conductor at an equivalent voltage sensitivity of 10 microvolt/cm is also demonstrated. The technique is simple, non-invasive, and applicable to a wide range of superconductor devices and beyond where thermal monitoring of interior of a solid object is required.
Air Liquide Advanced Technologies started the development of Turbo-Brayton refrigerators with the goal to have a reliable, plug and play, maintenance-free and efficient solution, introducing oil-free centrifugal compression and single skid system. These refrigerators are able to cover a wide range of temperature between 35K and 150K. This product is particularly adapted for High Temperature Superconductivity refrigeration at 65-70K. The development of HTS cables technology and the market growing will lead to the need for higher cold power as the length of the cable is increasing. This is why the range has been extended and new products are now available, going from 7 to 50kW@77K. As an illustration of this need, 20kW@70K are requested for the ComEd project in Chicago and a TBF-350 unit will be delivered in 2017. The first TBF-350 was manufactured and tested in June 2016. A complete test protocol was defined and this paper presents the commissioning results of the refrigerator.
A superconducting transmission line is being developed for applications requiring distribution of electric power among a number of locations along its length.
AC losses are inevitable to be considered for effective design of High Temperature Superconducting (HTS) cables. Various analytical techniques are available to estimate these AC losses however not sufficient to accurately predict the same. Hence, computational methods are being widely used in the prediction of AC losses as the experimental techniques are complicated to be implemented. YBCO (Tc=90K @ 0T) and BSCCO (Tc=110K @ 0T) are generally used in the construction of HTS cables. However, the critical temperature reduces as the external magnetic field is experienced by the tapes increases giving lower temperature margin for cooling purposes. In the present work, Computational Electrodynamics (CED) is used to predict the AC losses in coated conductors (Second Generation) HTS tapes used in constructing the HTS cables. These losses which are dissipated as heat must balanced by the cooling the requirements. The effect of external magnetic field on the degradation of critical current is examined. Finite Difference Time Domain (FDTD) approach is used for discretization of governing equations in solving for the AC losses. Further, electric field distribution in coated conductors due to the applied magnetic field is investigated. Hence, the results of the present analysis guide the thermohydraulic design of HTS cables.
Typically high temperature superconducting (HTS) cables utilize solid dielectric materials such as PPLP and Cryoflex for electrical insulation layer. A solid dielectric is destroyed once an electrical breakdown has occurred. However, a gaseous dielectric design retains the same dielectric strength once breakdown has occurred. Research at the Center for Advanced Power Systems (CAPS) has focused on developing a gaseous helium (GHe) cooled HTS cables in which GHe acts as the sole dielectric material. To assess the ruggedness of gas insulated HTS cables against multiple breakdown events, it is necessary to assess the effect of breakdown events not just on the gaseous insulation medium, but also on the HTS tapes. It was therefore decided to study the effect breakdown events on the critical current of HTS tapes. The superconductive layer only represents approximately 1% of the total crossection of a typical second generation HTS tape. Studies have been performed on the critical critical current of HTS tapes before and after breakdown events. The ability of a HTS cable to be suitable for operation after multiple electrical breakdown events is an important characteristic of a superconducting gas insulated cables. This paper will present the details of the breakdown experiments performed and their effect on the critical current of several types of commercially produced HTS tapes. This work is funded by the Office of Naval Research.
In the stage Ⅲ(2016 – 2018) of JST/Strategic Innovation Program, 4 teams are developing HTS application prototypes to demonstrate to verify fundamental component technologies such as DC power cables for railway, compact accelerator magnets, high field NMR systems, and SQUID systems. Main targets of this program are to establish fundamental component technologies for each application and to demonstrate prototypes incorporating these technologies.
Typical achievements to date are as follows;
(1) Design of HTS DC cables for railway application and demonstration of application of HTS DC cable in a commercial railway was tried.
(2) Prototype of HTS model magnet for accelerators have been developed.
(3) High-field NMR system have been developed, including high sensitive probe and compact NMR magnets using HTS materials.
(4) HTS SQUID systems for medical and biotech have been developed.
Details of R&D achievements will be introduced.
Refrigeration at 2 K and below has become the new standard in cryogenically cooled particle accelerators. Up to four cryogenic turbo compressors need to be operated in series in order to reach the required sub-atmospheric helium bath pressure. Such highly developed systems shall operate at high reliability not interrupting the entire research facility. Linde Kryotechnik successfully supplied several cold compressors over the last 20 years. This long experience is the basis for a deeper understanding of the behavior of such sophisticated systems. Typical process arrangements for transient and part load operation, optimized control concepts as well as potential risks and corresponding mitigation measures will be discussed.
Together with the unique in-house developed control logics for multistage cold compressors these machines present a fully packaged solution for highly efficient and reliable refrigeration at 2 K and below.
In order to effectively characterize the performance of the cryo-viscous compressor (CVC) prototype, supercritical helium (SCHe) was required in order to mimic the conditions that the CVC would see in its installation site at ITER. Given the specific requirements for SCHe (2.0 g/s, 4.5 K, and 3.0 bara), a collaboration between US ITER and the Spallation Neutron Source Research Accelerator Division cryogenic group resulted in the utilization of existing infrastructure, the Cryogenic Test Facility (CTF), to achieve these conditions. While the CTF is normally used in superconducting radio frequency R&D, it has the ability to provide two distinct SCHe flows with a total flow rate of 10.0 g/s, temperatures near 4.5 K, and at pressures approaching 6 bar. A network of vacuum jacketed transfer lines piping and flow control interfaces was designed, fabricated, and installed to supply 2.0 g/s of SCHe to the CVC, while utilizing the remaining SCHe as a shield supply to minimize heat load to the supply and provide a 100 L liquid He precooler to reduce the supply temperature. A description of the individual components and their performance in the successful demonstration testing of the CVC will be presented.
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. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
To effectively process the mixed exhaust from the regeneration of the ITER torus cryopumps, a cryo-viscous compressor (CVC) prototype has been designed, fabricated, and subjected to successful performance testing. This testing, which was performed at the Spallation Neutron Source Cryogenic Test Facility, involved cooling a set of twenty-four 5-cm diameter, 1.27-m long stainless steel tubes with embedded static mixer flow enhancements with supercritical helium (SCHe) at flow rates between 1.0 g/s and 8.0 g/s, supply temperatures near 5 K, and supply pressures near 2.6 to 2.7 bara. The CVC prototype was able to cryopump deuterium at all SCHe flow rates from helium/deuterium process gas mixtures at helium percentages between 0.1% and 2.0% and at peak process gas flow rates up to 366 Pa-m3/s (0.6 g/s). Once the deuterium was cryopumped, regeneration operations were completed over a 15 to 20 minute period through the introduction of 30 K “warm” He gas to remove the deuterium from the CVC. In addition to the functional responses of the CVC prototype, performance considerations for the CVC once installed within the ITER vacuum system are presented.
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. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
The linear compressor for cryocoolers possesses the advantages of long-life operation, high efficiency, low vibration and compact structure. It is significant to study the match mechanisms between the compressor and the cold head, which determines the working efficiency of the cryocooler. However, the output characteristics of linear compressor are complicated since it is affected by many interacting parameters. The existing matching methods are simplified and mainly focus on the compressor efficiency and output acoustic power, while neglecting the important output parameter of pressure ratio. In this study, a mechanical phasor model basing on analyzing the forces of the piston is proposed. It can be used to predict not only the output acoustic power, the efficiency, but also the pressure ratio of the linear compressor. Calculated results agree well with the measurement results of the experiment. By this phasor model, the theoretical maximum output pressure ratio of the linear compressor can be calculated simply based on a known charge pressure and operating frequency. Compared with the mechanical and electrical model of the linear compressor, the new model can provide an intuitionistic understanding on the match mechanism with faster computational process. The model can also explain the experimental phenomenon of the proportional relationship between the output pressure ratio and the piston displacement in experiments. By further model analysis, such phenomenon is confirmed as an expression of the unmatched design of the compressor. The mechanical phasor model may provide an alternative method for the compressor design and matching with the cold head.
The loss of insulating vacuum is often considered as a reasonable foreseeable accident for the dimensioning of cryogenic safety relief devices. The cryogenic safety test facility PICARD was designed to investigate such events. In the course of first experiments, discharge instabilities of the spring loaded safety relief valve occurred, the so-called chattering and pumping. These instabilities reduce the relief flow capacity, which leads to impermissible over-pressures in the system. The analysis of the process dynamics showed first indications for a smaller heat flux at opening pressure than the commonly assumed 4 W/cm2, resulting in an oversized discharge area for the correspondingly reduced relief flow rate.
This contribution presents further experimental investigation, where the insulating vacuum was vented with atmospheric air under variation of the venting diameter, the size and the set pressure of the safety relief valve and the helium filling level. Based on dynamic process analysis, the results are discussed in terms of effective heat fluxes and operating characteristics of the spring-loaded safety relief valves.
The sudden loss of insulating vacuum is a potentially severe event to be considered in the safety analysis of cryogenic applications. When insulating vacuum is broken, large heat fluxes can heat up and expand cryogenic fluids inside the vacuum-insulated apparatus in a very short time.
The effect is particularly pronounced in applications involving helium, hydrogen and neon at temperatures below the condensation temperature of air, where air condensation on the cold surfaces leads to instantaneous peak heat fluxes that have been reported to be on the order of tens of kilowatts per square meter in some cases.
The effect is currently being investigated at several institutions worldwide. However the incorporation of the vacuum loss scenario into the safety design, and particularly the sizing of relief devices of cryogenic apparatus based on existing norms and standards, is not immediately obvious. We take a look at existing norms and present a way forward which we consider to be prudent and appropriate.
Reclassification of diesel engine exhaust as a carcinogen, has led to the mining industry exploring zero-emission alternatives to power underground mining equipment. Most interest lies with electric driven mining machines, however a new possibility is engines fueled with cryogens. This research conducts a formal risk assessment for cryogenic fueled equipment in underground environments. These include fans, load haul dump units, and trucks. The motivating advantage is zero-emissions production in the subsurface and simultaneous provision of cooling for ultra deep mine workings. The driving force of the engine is the expansion of the reboiled cryogen following flash evaporation using ambient temperature heat. The cold exhaust mixes with warm mine air and cools the latter further. The use of cryogens as 'fuel' leads to much increased fuel transport volumes and motivates special considerations for distribution infrastructure and process including: cryogenic storage, distribution, handling, and transfer systems. Detailed specification of parts and equipment, numerical modelling and preparation of design drawings are used to articulate the concept. The conceptual design process reveals new hazards and risks that the mining industry has not yet encountered, which may yet stymie execution. The major unwanted events include the potential for asphyxiation due to oxygen deficient atmospheres, or physical damage to workers due to exposure to sub-cooled liquids and cryogenic gases. The Global Minerals Industry Risk Management (GMIRM) framework incorporates WRAC and Bow-Tie techniques and is used to identify, assess and mitigate risks. These processes operate upon the competing conceptual designs to identify and eliminate high risk options and improve the safety of the lower risk designs.
In the event of an underground mine emergency that makes the ambient air irrespirable, mineworkers need to use Self-Contained Breathing Apparatus (SCBA) for escaping or to be rescued, and if trapped, be provided with breathable air to sustain life in shelters termed Refuge Alternatives. NIOSH explored cryogenic technologies for these applications and with the help of NASA built Cryogenic Breathing Apparatuses (CryoBA) for continued escape, Air Storage and Filling Stations (CryoASFS) for refilling CryoBAs along the escape route, Refuge Alternative Storage Systems (CryoRASS) for life support and cooling and a Liquid Oxygen Kit (LOXK), for closed circuit long duration rescue breathing apparatuses. The prototypes developed are described in this presentation together with their design specifications. Two versions with single and twin dewars of the CryoBA, which are open-circuit SCBA were built with refilling capability via a CryoASFS while being worn on the user’s back. The CryoASFS and CryoRASS stored the cryogen in large dewars, preventing commodity loss before use by employing cryocoolers in their designs. The CryoRASS employs a delivery module that recirculates and adds breathing gas within and into the shelter, while providing cooling inside it including removing moisture. The prototypes functioned well and were demonstrated on the surface and underground. The cryogenic SCBA prototypes were shown to be capable of meeting performance standards for subsequent approval of production grade units for underground mine use in USA. One manufacturer has shown an interest towards producing the CryoBA and CryoRASS and getting the respective approvals.
Cryostats contain large cold surfaces, cryogenic fluids, and sometimes large stored energy (e.g. energized magnets), with the potential risk of sudden liberation of energy through thermodynamic transformations of the fluids, which can be uncontrolled and lead to a dangerous increase of pressure inside the cryostat envelopes. The consequence, in the case of a rupture of the envelopes, may be serious for personnel (injuries from deflagration, burns, and oxygen deficiency hazard) as well as for the equipment. Performing a thorough risk analysis is an essential step to identify and understand risk hazards that may cause a pressure increase and in order to assess consequences, define mitigation actions, and design adequate safety relief devices to limit pressure accordingly. Lessons learnt from real cases are essential for improving safety awareness for future projects. We cover in this paper our experience on cryostats at CERN and the design-for-safety rules in place.
High-temperature superconducting (HTS) materials offer a mature core-technology for propulsion motor/generators in transportation. In Japan, 1-3 MW synchronous motors for ship propulsion have been developed by industry-national institute-academia liaison using HTS wires. As alternative choice for field poles, melt-growth bulk HTS provides a successful design and making of prototype modules for 10-30 kW rotating machines. An effective magnetization for the HTS bulks is a key to achieving a high magnetic flux density, which provides a superior field pole compared with conventional machines. For practical applications, the pulsed field magnetization (PFM) after cooling below Tc continues to be developed to attain a compact fixture. Employing several milliseconds rise time and a duration of four seconds with a waveform control made by active feedback of the Hall sensor voltage as a function of time, the HTS bulk traps a high magnetic flux density that exceeds 90 % of that obtained by conventional and slow field cooled magnetization. In a rotating machine application, the design of the armature/magnetization coil must meet the requirements of the field-pole bulks and be compact and light weight. In contrast to HTS tape-wound coils, using either 1G and/or 2G wires, active control of the magnetic flux generated by dc pulsed current control can be accomplished by applying complementary magnetization or demagnetization. Research also continues on the magnetic flux dynamics towards an optimum set of PFM parameters. A Neon thermosyphon cooling has been applied to enhance and control useful field pole strength. In large output power applications, such as wind/ocean renewable energy generators and ship/aeronautic propulsion motors, these machines are highly desirable because of their potential for high energy density per weight/volume. In this paper, we review the current status, and the worldwide progress with the development of superconducting PM machines.
Superconducting electric machines have shown potential for dramatic increases in power density for applications such as offshore wind generation, marine propulsion, and turbo-electric distributed aircraft propulsion. Superconductors exhibit zero loss when in dc conditions, though ac current produces considerable loss due to hysteresis, eddy currents, and coupling. For this reason, many present machines are designed to be partially superconducting, meaning that the dc field components are superconducting while the ac armature coils are normal copper conductors. Fully superconducting designs can also provide increases in power density due to a significantly higher peak armature current; however, ac loss analysis is then required to determine the feasibility of the machine’s intended operating conditions.
This research aims to characterize the expected losses in a fully superconducting machine targeted towards aircraft, whose design is based on an actively-shielded, partially superconducting machine from prior work. Various factors are examined such as magnet strength, operating frequency, temperature, and machine load to produce a model for the loss in the superconducting components of the machine. This model is then used to optimize the design of the machine for minimal ac loss while maximizing power density.
High temperature superconductive (HTS) power machines, such as a power cable, a transformer and a fault current limiter, have been tried to approach commercialization recently. In commercializing of HTS power machines, a cooling system shall have cooling capacity from 2kW to 10kW at 70 K, long maintenance interval and high efficiency (low input power). The HTS power machines are cooled by circulating of sub-cool liquid nitrogen and returned liquid nitrogen from HTS power machines will be cooled down using refrigerator. There are few kind of refrigerator for cryogenic field. A Stirling cycle refrigerator and a turbo-Brayton cycle refrigerator will be candidate to cool HTS power machines.
Taiyo Nippon Sanso Corporation had been developed a 2kW class turbo-Brayton cycle refrigerator in NEDO project from FY 2008 to FY 2012. The 2kW refrigerator is using Neon gas as working fluid. And an active magnetic bearing was adopted for turbo-compressor and turbine of the refrigerator. That is one of an advantage for applying HTS power machines. Because the magnetic bearing can levitate the shaft of the turbo machines therefore the refrigerator can become long term maintenance interval. After developing of 2kW refrigerator, 10kW turbo-Brayton refrigerator also has been developed for long length HTS power cable. Two types of refrigerator have operation experience about one year in field test.
Present status and technology detail of turbo-Brayton cooling system will be introduced in this presentation. And also subjects of turbo-Brayton cooling system for applying to electric propulsion aircrafts will be discussed.
As useful applications for superconductors continue to expand, required cooling methods still tend to be custom tailored for each application. The performance, capabilities, and economies of varying cryogenic cooling options are therefore an important concern for machine designers and end users. Features that are critical in the initial design and must be included in trade-offs when analyzing the options include many criteria, including weight, size, geometry, capacity at temperature, cooling rate from ambient, sensitivity to the environment (gravity, vibration, motion etc..), machines lifetimes, and also machine acquisition and lifetime costs. Since weight is critical for air and space applications, and short mission cycles from minutes to days are typical, different options for cooling need to be considered, including liquids with freezing points from 112K (natural gas), to 20K (liquid hydrogen), to 4.2K liquid He, and hybrid systems incorporating cooled liquids as upper reservoirs with multi-stage cryocoolers for lower temperatures. Solid-cryogens are also of interest for short-missions. AFRL is interested in cutting edge applications incorporating both low- and high-temperature-superconductors (LTS and HTS), and therefore has great interest in a broad range of cryocooling capabilities.
Herein we present a survey and comparison of cryocooling technology options, including traditional mechanical cryocoolers, and also properties of liquid cryogen cooling storage and liquification technologies. Efforts are made to include the parameters critical for aerospace systems, and transient missions. While many reviews are available in the literature, they do not always consider specific masses for varying machine input powers. Also updates for cryocooler technologies will be provided, for a limited survey.
Acknowledgements: Air Force Office of Scientific Research (AFOSR) and The U.S. Air Force Research Laboratory, Aerospace Systems Directorate (AFRL/RQ)
The authors give an overview of cooling technologies for cryogenic transportation machines that are most promising, followed by a brief survey and analysis in which way commercially available cryocoolers could be applicable.
This talk will review the status of 2G HTS wire production and integration at SuperOx, with an emphasis on the recent facility expansion at the Moscow location.
As of January 2017, full production cycle of 2G HTS wire has been established at SuperOx in Moscow. This includes the commissioning of a new buffer deposition line in January 2016 and of a new PLD-HTS deposition system in December 2016. These new facilities were installed in addition to the similar existing production facilities at SuperOx Japan LLC, which remain in operation. The expansion essentially doubled 2G HTS wire production capacity of the SuperOx group of companies. The wire produced at both locations is of identical high quality.
We will also present an overview of our industrial R&D programmes run in parallel with wire production, which are aimed at improving the wire performance in magnetic field, optimising buffer layer architecture, expanding the range of customisation options, etc.
In addition to the HTS material production, SuperOx has been developing HTS devices such as cables, fault current limiters, coils, rotating machines, current leads, and 2G HTS composite bulk. Examples of the SuperOx HTS device activities will be given in the talk.
REBCO coated conductors are produced nowadays in lengths long enough for first demonstrative applications. Due to that also several HTS cable concepts are being developed, as Roebel Assembled Coated Conductor (RACC) cable, Coated Conductor on Round Core (CORC) cable and diverse stack cable concepts.
Approaching demonstrative applications, middle lengths of the RACC cable need to be assembled and supplied. Going from short length (couple of meter) to intermediate lengths (∼ 30 m) is a significant development step due to coated conductor geometrical inhomogeneity’s and strand forming technology issues. Up to now in the HTS cable development the focus is mostly on critical current (Ic) requirements. Thinking about long length not only Ic criteria but also geometrical homogeneity and superconducting properties homogeneity across and along the tape need to be taken into account.
Thanks to EU project EuCARD2 and its ‘’future magnets’’, development task for HTS magnets for accelerator use the cable development is pushed forward. Such accelerator focused demonstrators need customized intermediate HTS cable length which were prepared by advanced routes and supplied for coiling.
The crucial steps from short lengths of the RACC cable (below 6 m) towards intermediate lengths (∼ 30 m) will be addressed in this contribution. Geometrical irregularities of the coated conductor will be quantified, qualified and compared with RACC strand inconsistency. Internal tape inequalities of the critical current will be quantified and qualified using transport methods as well as induction measurement methods. A new punching tool for strand preparation in collaboration with CERN designed on basis of the collected experience led to significantly improved strand performance. First results with the impact on the cable performance will be shown.
Two new ReBCO-CORC based Cable-In-Conduit Conductors are developed by CERN in collaboration with ACT-Boulder. Both conductors feature a critical current of about 80 kA at 4.5 K and 12 T. The first conductor is designed for operation in large detector magnets, while the second is aimed for application in fusion type magnets. The conductors are using the six-around-one cable geometry with six flexible ReBCO CORC strands twisted around a central tube. Each cable comprises six CORC strands each having 42, 4mm wide Superpower SCS4050 tapes with a 5 µm copper layer for a total of 252 tapes per conductor. The cable layout in both conductors is practically the same but they feature different jacket material and cooling mode. Detector type magnets require stable, high-current conductors and conduction cooling is highly preferred for its simplicity. Therefore, this CORC Cable-In-Conduit Conductor comprises an OFHC copper jacket with external conduction cooling. Contrary the heat load on most superconducting magnets in a fusion plant is too high for allowing a conduction cooled conductor. Therefore, the second conductor has internal forced flow cooling through the central tube and voids between the CORC strands. In addition, the cable is enclosed by a stainless steel jacket to cope with the high level of Lorentz forces in such magnets. A 2.8 m long sample of each conductor is manufactured and prepared for testing in the Sultan facility at PSI Villingen. In the paper the conductor design and assembly steps for both record size CORC type Cable-In-Conduit Conductors is highlighted.
A Bi2212-based rectangular wire approach has been developed, with up to 400 MPa stress tolerances and useful current densities for building transposed cables that are problematic with wide HTS tapes, and that need to operate beyond the field and temperature limits of low temperature superconductors. We are applying this recently established Bi2212-wire capability to develop robust, transposed, HTS cables for use in winding large, relatively low inductance magnets where ramped- or ac-field conditions require narrow, low-loss wires in transposed, high winding current, cabled configurations. As a first step, we modified a commercial, planetary 6-strand machine for cabling our wires with thicknesses / widths in the 0.5 – 1 mm / 0.8 – 2 mm ranges. The operational capability of the setup, as well as settings and calibrations were established using copper wires with similar dimensions to our Bi2212 wires. Bend tests of the reinforced Bi2212 wires in their pre-reacted conditions also demonstrated that they could be edge bent to ~1 cm diameter without indications of damage, and following reaction after bending, without adverse effects on Ic / Je, thereby underpinning our development objectives. Subsequently, transposed 6-wire samples were cabled to an ~ 4.5 cm pitch length using wires in their pre-reacted conditions. The cables exhibited flat top and bottom surfaces, without indications of wire damage. Bend tests indicated that they could be bent to minimum diameters of about 5 cm, and as a result a number of 6 cm inner diameter initial test coils have been produced, followed by reaction to form high Jc 2212. Ic test data demonstrated that they exhibited very useful transport current density levels. These results pave the way towards development of first-of-their-kind, transposed, robust, high-current, narrow-wire HTS cables that are of interest for winding some advanced particle accelerator and fusion reactor development magnets.
Advanced Conductor Technologies is developing high-temperature superconducting Conductor on Round Core (CORC®) magnet wires, wound from REBCO tapes with 30 μm thick substrates, for use the accelerator magnets. Round, isotropic CORC® wires of 3-4 mm thickness could offer operating currents in excess of 10,000 A and engineering current densities Je of over 600 A/mm2 at 4.2 K and 20 T, while allowing bending to diameters below 50 mm. CORC® wires are a very attractive candidate for use in Canted-Cosine-Theta (CCT) magnets in which the dipole field is generated by winding an even number of layers at opposite tilt angles.
Lawrence Berkeley National Laboratory is developing magnet technologies for dipole fields beyond 16 T by combining a CCT outsert, wound from low-temperature superconductors, with a CCT insert wound from high-temperature superconductors. Here we focus on insert magnets based on the CORC® wires. The CCT insert magnet will be developed in several steps, including a double-layer, 40 turn per layer CCT magnet (C1) wound from CORC® wires containing 16 superconducting tapes and a 4-layer, 40 turn per layer CCT magnet (C2) wound from high-Je CORC® wires containing 29 tapes. The results of two double-layer, 3-turn, sub-scale CCT magnets containing CORC® wires with the C1 and C2 architecture, and that of CCT magnet C1 wound from a total of 40 meters of CORC® wire are presented. The dipole field in the magnet aperture was measured in self-field in liquid nitrogen and liquid helium up to the critical current. The results show a clear path forward to achieve at least 5 T in the CCT insert magnet that would operate in a background field of 15 T resulting in a total field of 20 T.
Acknowledgement
This work was supported by the US Department of Energy under agreement numbers DE-SC0009545, DE-SC0014009, DE-SC0015775 and DE-AC02-05CH11231.
This paper focuses on the second stage regenerator of a 4K Gifford-McMahon (G-M) cryocooler. A three-layer layout of lead (Pb), HoCu2 and Gd2O2S spheres in the second stage regenerator derives a good performance at the temperature of 4 K. From the latest test, we confirmed that the cooling power of 1.60 W at 4.2 K was achieved by using this three-layer layout. The two-stage G-M cryocooler is RDK-408D2 (SHI) and the compressor is C300G (SUZUKISHOKAN) with an electric input power of 7.3 kW at 60 Hz. In order to further improve, a new regenerator structure that was named a double pipe regenerator developed by Masuyama in 2016 was applied to the second stage regenerator. As a double pipe, a stainless steel pipe with thin wall was inserted in the coaxial direction into the second stage regenerator. The helium flow in the second stage regenerator is expected to be non-uniform flow because of the distribution of helium density and the imperfect packing of regenerator material. The double pipe regenerator is considered to have an effect which rectifies the helium flow. From the experimental result, the cooling power was improved by 1.67 W at 4.2 K. This result proves that the double pipe regenerator is an effective method to improve the cooling power.
Compared to rotary motor driven Stirling cryocoolers, linear motor coolers are characterized by small volume and long life, making them more suitable for space and military applications. The linear motor Stirling coolers are directly driven by a linear motor and both the components are integrated as a single unit. Therefore, the motor characteristics have direct effect on the operation of the cooler. In this context, plenty of scope exists in understanding the behavioral features of linear motor systems. In the present work, the authors compare and analyze the moving magnet linear motor with and without teeth to finalize the geometry suitable for the Stirling cryocooler. The required axial forces in the linear motors are generated by the current flowing in a magnetic field. The compact size, commercial availability of permanent magnets and low weight requirement of the system are quite a few constraints for the design. The finite element analysis using Maxwell software serves as the basic tool to analyze the magnet movement, flux distribution in the air gap and the saturation levels on the core. A number of material combinations are tried out for core before finalizing the design. The effect of varying the core geometry on the flux produced in the air gap is also analyzed. From the analysis, it is observed that the motor without teeth is advantageous over the motor with teeth in terms of effective utilization of magnetic flux in the air-gap in order to provide the required force.
The cooling power of stirling cooler is the most important performance. But in some special field, for example in IR seek, the cooling down time was more important. Thus, it is a great challenge for improving cool down time of the stirling cooler. A new model SCI09H split Stirling linear cryogenic cooler was designed by us. A new structure of linear motor was used in the compressor, and the machine spring was used in expander. In order to reducing the cooling down time, the stainless steel mesh of regenerator is optimized. The cooler’s weight is 1.1 Kg, the cooling down time to 80K is 2 min at 23℃ with a 250J thermal mass, the cooling power is 1.0W at 80K, and the input-power is 60Wac.
Sub-kelvin refrigerator has many applications in space detector and manned space station, such as for the transition-edge superconducting (TES) bolometers operated in the 50 mK range. In order to meet the requirement of space applications, the high efficient, vibration free and high stability refrigerator need to be designed. VM/PT hybrid cryocooler is a new type cryocooler capable of attaining temperature below 4K. As a low frequency Stirling type cryocooler, it has the advantages of high stability and high efficiency. Combined with the vibration free sorption cooler and ADR refrigerator, a novel sub-kelvin cooling chain can be designed for the TES bolometer. This paper presents the recent experimental progress of the 4K VM/PT hybrid cryocooler in our laboratory. By optimizing of regenerators, phase shifters and heat exchangers, a lowest temperature of 3K was attained. Based on this cryocooler, a preliminary sorption cooler was designed and built.
We have been developing large Stirling cryocooler for cryogenic cooling system of HTS electric power devices. The developed Stirling cryocooler is driven by a dual-opposed linear compressor and has a gamma-type configuration. Three Stirling cryocoolers are integrated to produce 2 kW of cooling capacity. The liquid nitrogen circulation loop is prepared to simulate the cooling system of HTS cable. The cold head of cryocoolers is designed and fabricated to remove heat from subcooled liquid nitrogen flow. The cooling capacity is measured from enthalpy difference between inlet and outlet of liquid nitrogen. In experiments, temperature and pressure at several points are measured as varying mass flow rate of liquid nitrogen. With experimental results, temperature distribution in cold-head, characteristics of heat exchanger for liquid nitrogen, and performance of liquid nitrogen pump are discussed.
An appropriate mixed gas fluid can provide lower temperatures and higher cooling power when used in a Joule-Thomson (JT) cycle than is possible with a pure substance. However, selecting gas mixtures to meet specific cooling loads and cycle parameters is a challenging design problem. Previous research at UW-Madison has been focused on developing computational tools that optimize compositions of gas mixtures for specific operating parameters. This study expands on prior research by exploring higher heat rejection temperatures, lower cold-end temperatures, and smaller recuperator sizes than previously investigated. A thermodynamic model of a mixed gas JT system has been developed and will be integrated with a mixture optimization model. This allows optimal mixture compositions and operating parameters to be determined for a mixed gas JT system with cold-end temperatures down to 110 K and hot-end temperatures above room temperature.
Regenerative heat exchanger is the most vital component in a Stirling cryocooler. The performance of the cooler depends on the thermal and hydrodynamic properties of the regenerator used in the system. The computational fluid dynamics (CFD) modeling is the best technique to design and predict the performance of a Stirling cooler. But the accuracy of the results depends on the hydrodynamic and thermal transport parameters used as the closure relations for the volume averaged governing equations. This paper proposes a new friction factor correlation based method to obtain the viscous resistance term D and the inertial resistance term C required for modeling the regenerator as a porous media using FLUENT. Using standard friction factor correlations, friction factor was obtained for flow of helium through different wire matrices and compared with the correlation proposed by Clearman et al. in terms of permeability and Forchheimer's inertial coefficient. Friction factor data obtained from Blass and Tong/London correlations are in agreement with that of Clearman et al. Viscous resistance term D and inertial resistance term C are calculated from this data and used to model the steady and oscillatory flow through the regenerator. Comparison of the predicted and experimental pressure drop reveals good predictive power of the correlation based method. For oscillatory flow, the predicted pressure amplitude and the phase at the regenerator exit are compared with the experimental data. The correlation based method could predict the pressure amplitude and the phase difference accurately. Using this method, Darcy permeability and Forchheimer's inertial coefficient are obtained for 200, 250, 300, 450 and 500 mesh regenerators. Parametric investigation was conducted on these regenerators under steady and steady - periodic flow conditions. The effect of different operating and geometric parameters on the performance of the regenerator are presented.
This paper mainly presents a numerical investigation on a VM type pulse tube cooler. Different from previous systems that use liquid nitrogen, Stirling type precoolers are used to provide the cooling power for the thermal compressor, which offers the flexibility of changing working temperature range of the thermal compressor. Firstly, main component dimensions were optimized to achieve a lowest no-load temperature. Then the dependency of system performance on average pressure, frequency, displacer displacement amplitude and thermal compressor cold end temperature were studied. Finally, based on the simulation results, distributions of acoustic power, enthalpy flow, phase relationship between pressure wave and volume flow rate are presented. A lowest no-load temperature of 5.15 K was predicted with an average pressure of 2.5 MPa, a frequency of 3 Hz, displacer displacement amplitude of 6.5 mm, ambient end and cold temperature of 300 K and 90 K, respectively.
Keywords
VM type Pulse Tube Cryocooler; Thermal Compressor; Cryogen-free; Numerical Simulation
Under the situation of sufficient heat energy and shortage of electric energy,the heat-driven refrigerators can exploit their advantages sufficiently. The experimental study of heat-driven coupled VM-PTC cryocooler with He4 has already obtained the on-load temperature blow 4K. For enlarging the application limits,the refrigerating capacity of VM-PTC cryocooler with He3 as the working fluid ,which has more potential physical properties,should be researched further. This paper bases on a VM-PTC model established by Sage software. In numerically study,the no-load temperature under different precooling temperature on intermediate cavity and heating temperature on hot cavity are considered. Also, the structure parameter of VM-PTC machine and its attachments are optimized by Sage. On the basis of above,the relationship between variable load and cold end temperature is studied at last.
VM cryocooler is one kind of Stirling type cryocooler working at low frequency. At present, we have obtained the liquid helium temperature by using a two-stage VM/pulse tube hybrid cryocooler. As a now kind of 4K cryocooler, there are many aspects need to be studied and optimized in detail. In order to reducing the vibration and improve the stability of this cryocooler, a pulse tube cryocooler was designed to get rid of the displacer in the first stage. This paper presents a detail numerical investigation on this pulse tube cryocooler by using the SAGE software. The low temperature phase shifters were adopted in this cryocooler, which were low temperature gas reservoir, low temperature double-inlet and multi-bypass. After optimizing, the structure parameters and the best diameters of orifice, multi-bypass and double-inlet were obtained. With the pressure ratio of about 1.6 and operating frequency 2Hz, this cryocooler could supply above 40mW cooling power at 4.2K, and the total input power needs no more than 60W at 77K. Based on the highest efficiency of 77K high capacity cryocooler, the overall efficiency of this VM type pulse tube cryocooler is above 0.5% relative Carnot efficient.
Since 2012, a new, compact Gifford-McMahon (GM) cryocooler for cooling superconducting single photon detectors (SSPD) has been developed and reported by Sumitomo Heavy Industries, Ltd. (SHI). It was reported that National Institute of Information and Communications Technology (NICT) developed a multi-channel mounted on a GM cryocooler of SSPD system. However, the size and power consumption reduction becomes indispensable to apply such system to the optical communication of AdHoc for mobile system installed in a vehicle. The objective is to reduce the total height of the expander by 33% relative to the existing RDK-101 GM expander and to reduce the total volume of the compressor unit by 50% relative to the existing CNA-11 compressor. In addition, considering the targeted cooling application, we set the design temperature targets of the first and the second stages to 1 W and 20 mW of heat load at 60 K and 2.3 K, respectively. In 2016, Hiratsuka reported that an oil-less compressor was developed for a 2K GM cryocooler. The cooling performance of a 2K GM expander operated by an experimental unit of the linear compressor was measured. A no-load temperature of below 2.1 K and the cooling capacity target of 20 mW at 2.3 K was successfully achieved with an electric input power of only 1.1 kW. After that, the compressor capsule and the heat exchanger, etc. were assembled into one vessel as a compressor unit, and a compact inverter electricity box was developed. Also, the noise vibration characteristics and the effect of the compressor unit inclination and the environmental temperature on the cooling performance were evaluated. The detailed experimental results are discussed in this paper.The research results have been achieved by the National Institute of Information and Communications Technology (NICT), JAPAN.
Thermodynamic performance of mixed-refrigerant Joule–Thomson cycle (MRJT) and pure refrigerant reverse Brayton cycle (RBC) for cooling 80 K ~ 120 K temperature-distributed heat loads was analyzed and compared in this paper. Nitrogen under various pressures was employed as the heat load. The research was conducted both under ideal and nonideal condition, adopting exergy analysis method. Both the two cycles were single-stage configuration. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distribution in each process of refrigeration cycle was also analyzed.
Under the ideal condition, the highest exergy efficiency and volumetric cooling capacity of RBC was obviously inferior to MRJT in 90 K ~ 120 K temperature zone. The large exergy loss in recuperative process was a critical reason for the low efficiency of RBC, which was caused by the inferior heat capacity match of warm and cold stream. As a large fraction of neon was added in the 80 K MRJT, the performance of recuperative and throttling process in MRJT degraded severely. Thus RBC could achieve higher exergy efficiency and volumetric cooling capacity than MRJT under certain operating pressures at 80 K. The simulation result under nonideal condition (extrinsic irreversibilities were considered) was similar with that under ideal condition. MRJT showed obvious advantages over RBC in exergy efficiency and volumetric cooling capacity in 90 K ~ 120 K, but still inferior to the RBC at 80 K. The exergy loss in nonideal expansion process of RBC was obviously larger than the throttling process in MRJT, especially at higher refrigeration temperatures. The high discharge temperature of RBC also lead to a large exergy loss in after cooler. The performance degradation of recuperative and throttling process was still account for the inferior exergy efficiency of 80 K MRJT.
The accuracy of correlations of colburn(j) and friction(f) factor has important effect on the accuracy of simulation results in the dynamic simulation of large scale cryogenic helium systems. However，air was commonly used as heat transfer medium to derive most correlations available in the literatures and experimental results. In order to study the heat transfer and pressure drop characteristics of the offset strip-fin heat exchanger in helium systems, the steady-state three-dimensional numerical models were built. Orthogonal arrangement was adapted to reduce the numbers of simulation. Re, fin length, fin height, fin space, fin thickness were chosen as the parameters in the orthogonal simulation. Through numerical analysis, the j and f factor correlations were developed under different Reynolds (Re<800), which can predict 90% simulation data within ±20% deviation. These results were compared with the existing results obtained by air to find the influence of different fluid medium. The general correlations of j and f presented here probably provides a selection in dynamic simulation of heat exchangers.
A 250 W@4.5 K helium refrigerator has been developed in the Technical Institute of Physics and Chemistry, CAS. To establish operation control strategies and provide a user friendly human machine interface, a dynamic real-time simulator has been developed for this helium refrigerator based on software EcosimPro and Siemens PLC S7-300. This helium refrigerator which consists of one screw compressor, two turbo expanders, ten heat exchangers and a 500 liters liquid helium reservoir is modelled by software EcosimPro. The PLC interactives data with EcosimPro model by OPC technology. The cool-down process of this 250 W@4.5 K helium refrigerator has been simulated. Comparison between simulation results and experimental data has been discussed. This dynamic simulator can be used as an operation training system.
Guo et al introduced the physical quantity entransy to describe the heat transfer ability of an object, and then use the entransy dissipation to measure the loss of such ability due to the irreversibility of heat transfer. Liu and Guo defined the entransy dissipation based-thermal resistance (EDTR) for heat exchanger. The formulation of EDTR by heat capacity and effectiveness is introduced in this paper and then EDTR and the exergy efficiency of heat exchanger are calculated in Collins cycle as the heat capacity varies. The relations between heat capacity and thermal resistance, thermal resistance and exergy efficiency are drawn while effectiveness of heat exchanger is given. Study results reveal the mechanism of the influence of turbine flow rate on productivity of liquid helium. The conclusion has guiding significance for turbine mass distribution in a helium liquefier.
The Linac Coherent Light Source II (LCLS-II), a 4 GeV continuous-wave (CW) superconducting electron linear accelerator, is to be constructed in the existing two mile Linac facility at the SLAC National Accelerator Laboratory. The first light from the new facility is scheduled to be in 2019. The LCLS-II Linac cryomodules consist of thirty-five, 1.3 GHz and two, 3.9 GHz superconducting cryomodules. The Linac cryomodules require cryogenic cooling for the super-conducting niobium cavities at 2.0 K, low temperature thermal intercept at 5.5-7.5 K, and a thermal shield at 35-55 K. The equivalent 4.5 K refrigeration capacity needed for the Linac operations range from a minimum of 11 kW to a maximum of 24 kW. Two cryogenic plants with 18 kW of equivalent 4.5 K refrigeration capacity will be used for supporting the Linac cryogenic cooling requirements. These cryogenic plants are based on the Jefferson Lab’s CHL-II cryogenic plant which uses the “Floating Pressure” design to support a wide variation in the cooling load. In this paper we describe the cryogenic process for the integrated LCLS-II cryogenic system with the help of a simulation for a 4.5 K cryoplant in combination with a 2 K cold compressor box, and the Linac cryomodules.
Abstract: In this paper, a dynamic modeling and simulation of a large-scale helium refrigerator was set up and analyzed. Numerical models of the critical equipment including a screw compressor, six plate-fin heat exchangers, two turbine expanders, and four pneumatic valves are individually developed. In order to increase the simulated accuracy of the temperature profile of the heat exchangers, every heat exchanger is divided into a number of zones. Taking metal properties of coldbox having temperature dependence into account, the logarithmic equation for calculating the thermo-physical properties of metal is used. The curves of 300~4.5K cool-down and warm-up processes of the 250W@4.5K helium refrigerator are acquired. The simulated results based on the actual geometrical parameters and characteristics curves of the critical equipment are compared with the experimental data. The deviations between the simulation and experiments are discussed, which is helpful to increase the accuracy of the model further. This modified model can be used to design and optimize other large scale helium refrigerators.
Keywords: Large-scale helium refrigerator; modeling; dynamic simulation.
Acknowledgement
This work was supported by the fund of the State Key Laboratory of Technologies in Space Cryogenic Propellants (SKLTSCP 1502) and National Research and Development Project for Key Scientific Instruments. (ZDYZ2014-1)
A helium phase separator with a condenser is under fabrication and assembly at National Synchrotron Radiation Research Center (NSRRC). The objective of a helium phase separator with its condenser is to separate two-phase helium flow and to re-condense vaporized gaseous helium with a cryo-cooler of Gifford-McMahon type. We developed a 100L helium phase separator with a small heat loss as a prototype, include resist radiation layers. The experimental results for the temperature difference and total heat load of the phase separator are consistent with simulation results; the deviation is within 20 %, which includes the effect of thermal conduction and thermal radiation. The total heat loss of the helium phase separator from experiment is 1.1 W and from simulation is 0.841 W. The mechanism of heat transfer in phase separator was investigated and is discussed. This paper presents the experiment and design of the condenser in the capacity of 100L separator.
The China Fusion Engineering Test Reactor (CFETR) is envisioned to be constructed in the 2020s and start operation in the 2030s, according to the roadmap of China magnetic confinement fusion development. The updated design of the CFETR magnet system consists of 12 toroidal field (TF) and 6 poloidal field (PF) coils, a central solenoid (CS) coil stacked with 6 modules and 12 correction coils (CC). These superconducting coils (including their model or prototype coils) need to be cold tested in a coil test facility. Therefore a 5 kW @ 4.5 K helium refrigerator is being designed and analyzed in the Institute of Plasma Physics Chinese Academy of Sciences. In the present study, a 3D conceptual engineering design of the horizontal refrigerator cold box is conducted. In order to validate the feasibility and optimize the design, the thermal-mechanical analysis of the cold box is performed, including the steady state thermal analysis and thermal-mechanical coupling analysis of the components and pipes. Besides, the thermal loads of the key components due to conduction and radiation are estimated. According to these analysis results, the cold box is iteratively optimized.
Abstract: In 300-80 K precooling stage, the temperature of the HP helium stream reduces to about 80K with achieving 73% of total enthalpy drop. Apart from the most common liquid nitrogen precooling stage, another 300-80 K precooling configuration with turbine(s) is employed in some helium cryoplant. In this paper, thermodynamic and economical performance of two kinds of 300-80 K precooling stage configurations has been studied at different operating conditions taking discharge pressure and isothermal efficiency of compressors, isentropic efficiency of turbines and liquefied rate as independent parameters. The exergy efficiency, total UA of heat exchangers and operating cost of two configurations are computed. This work will provide a reference for choosing 300-80 K precooling stage configuration during design.
Keywords: cryogenic, helium refrigeration, thermodynamic analysis, liquid nitrogen precooling
The commercial applications of Superconducting Fault Current Limiters (SFCL) in electrical power systems are enormously increasing due to the production of long length high temperature superconducting (HTS) tapes. SFCL are preferred in electrical utility networks due to their better technical performance during faults when compared with the conventional Circuit Breakers. The self triggering from superconducting state to normal state during fault and very fast recovery to its superconducting state after fault removal is the basic operation of Resistive type Superconducting Fault Current Limiter (R-SFCL). This is designed using coated conductors (CC’s) strategically for power applications. In the present work, based on the thermo-electrical strategies, an R-SFCL for three phase transmission and distribution is developed. The investigation is carried for the short circuit behaviour in 440kV/1.2kA (Indian scenario) capacity under fault currents. Furthermore, the strategy to develop R-SFCL, fault recovery under load is studied and fault recovery time also calculated. A critical comparison is done for normal operation and fault current conditions.
Explored in the framework of the Research Training Group “Lorentz Force Velocimetry (LFV) and Lorentz Force Eddy Current Testing”, the target of this work is to develop the Lorentz Force Flow-meter (LFF) – a contactless technique for flow rate measurement of conducting liquid. By measuring the reaction force of magnetic source, induced by eddy currents, the flow rate of fluid with known conductivity is quantified. Remarkably, due to non-invasive measuring, this method has a great potential to be exploited for aggressive media (e.g. electrolytes), such as glass and salt melts. The main goal of a current research is to extend the LFF to the flow rate measurement of weakly conducted and slow fluids by virtue of the high magnetic field generation tailored with precise force measurements. The high-temperature bulk-superconducting (HTS) magnet system is proposed to integrate the LFF rendering significantly superior magnetic field and passing the maximum field of previously exploited Halbach NdFeB permanent magnet system [1,2]. Especially, the adapting its design to increase the resolution up to 1 nN of the force measurements system must meet the strict specifications, which range from load restriction needed to ensure precise force measurement, to the entire LFF system. Current contribution outlines the design and development of the appropriate refrigeration (cryostat) for the magnet system, based on HTS bulks. Furthermore, it discusses the experimental results of generated magnetic field. Concluding, numerical simulations examine the volumetric flow rate measurement of low conducting and slow electrolytes.
[1] B. Halbedel et al., Journal of Flow, Turbulence and Combustion, V.92, p.361-369, (2014)
[2] M. Werner et al., IEEE Trans. On Magnetics, V.48, N.11, p.2925-2928, (2012)
The authors acknowledge the German Research Foundation (DFG) within the Research Training Group “Lorentz Force Velocimetry and Lorentz Force Eddy Current Testing” (RTG-1567/3) for the financial support.
This work describes electromagnetic, mechanical and thermal modeling studies of conduction cooled MRI magnets wound using MgB2 and Nb3Sn superconducting strands. The goal is to substantially decrease the whole system cost and sitting cost by reducing the conductor needed, as well as the system footprint and sitting requirements. In this work we present magnet designs optimized for the conductor critical surface and our designed operational factors. We focus here on 2G MgB2 conductors and Tube–design Nb3Sn conductors, which have both a high Ic performance and enhanced stability at low fields. We used the Finite Element Method (FEM) modeling to determine the magnetic, thermal and mechanical properties of such MRI magnets. From the maximum magnetic field in the magnet winding the magnet load line was constructed which allowed the critical current of the magnet to be determined based on Ic (B) curve of the MgB2 and Nb3Sn strands, taken from experiments. Mechanical stresses in the windings have been calculated and compared with critical stresses of the MgB2 and Nb3Sn strands. Cooling and heating properties of the MgB2 and Nb3Sn windings were studied by thermal modeling using realistic input parameters obtained from experiments.
A pulsed, modular HTS electromagnet for energy storage applications was constructed and tested. Charge and discharge pulses are accomplished in about one second. A recuperative cryogenic cooling system supplies 42 to 80 Kelvin helium gas to the electromagnet. A practical solution to overvoltage and overcurrent protection has been implemented digitally using LabVIEW. Voltages as little as 46 micro-volts greater than the expected value trigger the protection system, which stops the pulse profile and begins an immediate current ramp down to zero over one second. The protection system has displayed its effectiveness in HTS transition detection and damage prevention. Experimentation has demonstrated that current pulses on the order of seconds with amplitudes of up to 110 Amps can be achieved for extended periods. Higher currents produce joint heating in excess of the available cooling from the existing cryogenic system.
In this work, we investigate the Metal-Insulator Transition (MIT) at very low temperature in presence of magnetic field using the competition between the relevant scale lengths determining the behavior of the electrical conductivity with low temperature in the both sides of the MIT. The MIT is induced by applying high magnetic field in 3D InP semiconductor sample. The scale lengths taking in account in this investigation are: the correlation length, the localization length, the interaction length and the hopping length.
The insulation materials used in the high field fusion magnets should be characterized by excellent mechanical properties, high electrical breakdown strength, good thermal conductivity and high radiation resistivity. Previous investigations by the authors showed that cyanate ester/epoxy (CE/EP) insulation material, a candidate insulation material for the fusion magnet, can maintain good mechanical performance at cryogenic temperature after 10 MGy irradiation and has a much longer pot life than traditional epoxy insulation material. In order to quantify the electrical properties of the CE/EP insulation material at low temperature, a cryogenic electrical property testing system cooled by a G-M cryocooler was developed in this study. The cryogenic electrical breakdown strength of the CE/EP insulation material was measured before and after irradiation.
Cable-in-conduit conductors of the ITER magnet system are directly cooled by supercritical helium. Insulation breaks are required in the liquid helium feed pipes to isolate the high voltage system of the magnet windings from the electrically grounded helium coolant supply line. They are submitted to high voltages and significant internal helium pressure and will experience mechanical forces resulting from differential thermal contraction and electro-mechanical loads. Insulation breaks consist essentially of stainless steel tubes overwrapped by an outer glass – fiber reinforced composite and bonded to an inner composite tube at each end of the stainless steel fittings. For some types of insulator breaks Glass – Kapton – Glass (GKG) insulation layers are interleaved in the outer composite. Following an extensive mechanical testing campaign at cryogenic temperature combined with leak tightness tests, the present paper investigates through non-destructive and destructive techniques the physical and microstructural characteristics of the low temperature high voltage insulation breaks and of their individual components, thus allowing to correlate the structure and properties of the constituents to their overall performance.
Development of novel electrical insulation is vital for successful fabrication of (S)-Insulator (I)-Superconductor(S) Josephson junctions and related devices that have potential applications in quantum computing, superconducting quantum interference devices (SQUIDs), single-electron transistors, remote sensors, and terahertz frequency (THz) signal generating and detecting devices. YBa2Cu3O7 (YBCO) based Superconductor (S)-Insulator (I)-Superconductor(S) Josephson junctions could operate at liquid nitrogen temperature and may have IcRn products (with Ic the junction critical current and Rn the normal resistance) at least one order of magnitude larger than in the low temperature superconductor based junctions. However, the development of these junctions has been a challenge for many years as the thickness of the insulating layer (I) in the junction is required to be only about a few nanometers thick and also provide high electrical resistivity. PBCO is a candidate for the fabrication of YBCO based Josephson junction because of its similar lattice structure, similar growth conditions, and identical thermal expansion coefficients. However, its electrical resistivity is still low to provide sufficient electrical insulation in the device. Here, we report growth and low temperature electrical transport studies of a new electrical insulation material, Fe doped (110)-oriented PBCO thin films.
In this work we tune the critical current for an Nb film with a rectangular array of antidots using a commercially available physical properties measurement system by varying several parameters, including temperature, magnetic flux, and current. Our measurements show variation in resistance through dips in the curves, which resemble Shapiro steps [1]. Since repeatedly performing such measurements may take an enormous amount of time and resources, we restrict our analysis to a small range of the parameters, and extrapolate the current-voltage curves to a wide range of those by means of artificial neural networks. Besides approximating the curves to perfection, we demonstrate that our approach may be adopted for other type of regular and diluted arrays of antidots.
The electrical insulation materials for use in ITER magnets and feeder system are required high voltage electrical breakdown strength. In order to develop good property insulation materials to satisfy the requirements of superconducting magnets, high voltage breakdown strength measurement system at low temperature is necessary. The high voltage breakdown strength measuring system in 1.8K with GM cryocooler has been partially constructed. In this paper, we will introduce the construction of the cryostat, the high voltage supply and control system including the needle-plate electrode, the cooling performance with the GM cryocooler, and the high voltage breakdown test results of the polyimide film in the cryogenic temperature.
Thermal expansion and magnetostriction, the strain responses of a material to temperature and a magnetic field, especially properties at low temperature, are extremely useful to study electronic and phononic properties, phase transitions, quantum criticality, and other interesting phenomena in cryogenic engineering and materials science. However, traditional dilatometers can not provide magnetic field environment easily and only been used in relative narrow temperature range (77-300 K). This paper describes the design and test results of thermal expansion and magnetostriction at cryogenic temperature using the strain gage method based on a Physical Properties Measurements System (PPMS). The interfacing software and automation were developed using LabVIEW. The sample temperature range can be tuned continuously between 2 K and 400 K. With this PPMS-aided measuring system, we can observe temperature and magnetic field dependence of the linear thermal expansion of different solid materials easily and accurately.
We have investigated the electrical transport properties of the insulating three-dimensional samples 70Ge: Ga p-type in the temperature range 0.05-2.7 K and in the absence of the magnetic field. The fourteen samples studied have Ga concentrations N ranging from 0.302 × 1017 to 1.84 × 1017 cm-3. On the insulating side of the transition, the study of the effect of low Temperature T on the electrical transport shown that the temperature dependence of the electrical conductivity is found to follow the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2 over the whole temperature range.This behaviour assumes that the carriers’ interactions reduces the Density Of State of carriers (DOS) in the vicinity of the Fermi leve and creates the Coulomb gap (CG).The data are for a 70Ge:Ga sample prepared and reported by Itoh et al. in Ref.[ K. M. Itoh, E. E. Haller, J. W. Beeman, W. L. Hansen, et al. Phys. Rev. Lett 77, 4058 (1996)] .
The paper is focused on comparison of conventional cold-rolling and progressive cryorolling processing. The material cooling at cryogenic temperature before rolling is provided by liquid nitrogen bath. Research deals with the changes in temperature of the material during the rolling process and deformation resistance dependence on strain. Further, the influence of plastic deformation on the properties of selected 316LN stainless steel and non-oriented electrical steel processed under cryo and ambient conditions was investigated. Microstructure was examined using the optical microscope and scanning electron microscope. According to the experimental study, there was found significant differences in the microstructure evolution between samples rolled in cryo condition. The results showed heterogeneous penetration of plastic deformation through thickness of the samples. Further, in cryorolled steels the deformations twins were observed. It has influence on final mechanical properties, which was tested by static tensile test. For high-nitrogen austenitic steel the tensile test at 293K, 77K and 4K was carried out. Main contribution of this study is that cryorolling followed by annealing provides higher mechanical properties compared with ambient conditions.
This work was realized within the frame of the project ”Technological preparation of electrotechnical steels with high permeability for electrodrives with higher efficiency”, which is supported by the Operational Program ”Research and Development” ITMS 26220220037, financed through European Regional Development Fund.
This paper covers cryogenic, tensile testing and research completed on a number of epoxies used in cryogenic applications. Epoxies are used in many different applications; however, this research focused on the use of epoxy used to bond MLI standoffs to cryogenic storage tanks and the loads imparted to the tank through the MLI. To conduct testing, samples were made from bare stainless steel, aluminum and primed aluminum. Testing involved slowly cooling test samples with liquid nitrogen then applying gradually increasing tensile loads to the epoxy. The testing evaluated the strength and durability of epoxies at cryogenic temperatures and serves as a base for future testing. The results of the tests showed that some epoxies withstood the harsh conditions while others failed. The two epoxies yielding the best results were Masterbond EP29LPSP and Scotch Weld 2216. For all metal surfaces tested, both epoxies had zero failures for up to 11.81 kg of mass.
The glass-fiber reinforced plastic (GFRP) fabricated by the vacuum bag process was selected as the high voltage electrical insulation and mechanical support for the superconducting joints and the current leads of ITER Feeder system. To evaluate the cryogenic mechanical properties of the GFRP, the mechanical properties of the GFRP such as the inter-laminar shear strength (ILSS), the tensile strength and the fatigue fracture strength after 30,000 cycles, were measured at 77K in this study. The results demonstrated that the GFRP met the design requirements of ITER.
Abstract: The origin of residual stress can be attributed to mechanical process, heat treatment, phase transformation and so on. There are many methods of residual stress release. Compared with heat aging and vibration aging, cryogenic treatment has many advantages in releasing of residual stress. The residual stress relaxation of 7050 aluminum alloy is investigated in the present work. In experiment, different processes of cryogenic treatment were performed on 7050 aluminum alloy. The change of residual stress was tested by blind-hole method and X-ray diffraction method respectively. Numerical simulation of cryogenic treatment process was conducted by finite element method, and the majority of the controlling parameters of cryogenic treatment have been taken into account. The experimental and numerical results show a good correlation.
Key words: Residual stresses; 7050 aluminum alloy; Cryogenic treatment; Finite element model
For the past couple decades, 316LN stainless steel has remained the “go-to” alloy for structural components intended for cryogenic temperature service, partially because of its favorable mechanical properties, but also because of the data available in the literature for T = 4 K. Some applications, for example the ITER Central Solenoid, require better room temperature strength and lower thermal contraction (295 K to 4 K) than 316LN which lead to the selection of two other high performance austenitic steels (Nitronic 50 and JK2LB). This study presents new 4 K fatigue crack growth rate (FCGR) and fracture toughness data for Nitronic 50 and JK2LB stainless steels, compiles existing data for these alloys, and compares them with 316LN data found in literature. This study intends to further expand the existing cryogenic data set for these alloys, clarify key differences between them to better facilitate mechanical design, and potentially bolster further alloy development.
High strength aluminum alloy AA2219 in T87 temper is widely used in fabrication of cryogenic propellant tanks. In the present work, tensile properties, fracture toughness and fatigue crack growth rate (da/dN) of AA2219-T87 sheet at room temperature, 153 and 90 K were investigated. The elastic-plastic J-integral fracture toughness was conducted with a compact tension (CT) specimen by means of unloading compliance method. The fatigue crack growth rate was conducted with a K-increasing test method. Fractographic analyses of fractured surfaces failed at room and low temperatures were performed and cryogenic mechanical properties were discussed.
Superconducting RF cavities are typically fabricated by forming cups from polycrystalline or large grained high purity Nb sheet material and welding these sections at the iris and equator to form a cavity string. An alternative approach is to form a tube into a monolithic cavity string by mechanical deformation. One problem with this approach is that inconsistent tube microstructure can lead to deviations in the cavity geometry or cracking in highly deformed regions. The work reported describes a method of applying severe plastic deformation to Nb tube in order to generate a uniform microstructure with radially symmetric texture that leads to excellent hydroforming performance. We will report hydroforming results from subscale (4cm OD) tubing and progress in our scale-up efforts.
Oxygen free high conductivity (OFHC) copper is the workhorse stabilizer for most low temperature superconducting wires and cables. It is also used for the pan-cake windings in Bitter electro-magnets. Copper is the material of choice for these applications because of its good electrical and mechanical properties, chemical compatibility with adjacent materials, and good joining characteristics. The material can be effectively work hardened to improve its strength without severe degradation of electrical conductivity. Because engineers would prefer stronger copper for many electrical applications, a study was undertaken to understand the limits of strengthening copper by work hardening and how well this strengthening holds up to subsequent heat treatment. Hardness, tensile strength, and electrical resistivity properties of C101 (OFHC), C110 (commercially pure), and C182 (Cu-Cr alloy) are reported for plastic strain levels to 8 and subsequent annealing to 500C. The story presented is enriched with microstructural characterization results and correlations between grain size and strength.
Magnetoencephalography (MEG) is an alternative noninvasive brain imaging technique that measures the magnetic field generated by neuron activities. MEG offers better temporal resolution than current imaging systems. Superconductor Quantum Interface Devices (SQUIDs) are the sensors used in MEG systems. High- transition-temperature-superconductor (HTS) SQUIDs could potentially improve the resolution and sensitivity of the images and reduce both fabrication and operation costs. However, most HTS SQUIDs are noisier than Low-Temperature Superconductor SQUIDs. Grain boundaries and twinned planes are some of the sources of noise in these materials. Therefore, in our research, we aim to investigate the noise caused by twinned grain boundaries. To reduce the noise, we propose a possible way of getting better lattice match between the substrate and the film using miscut lanthanum aluminate - strontium aluminum tantalate (LSAT) at different angles with the YBa2Cu3O7-δ (YBCO) layer. Commonly, LSAT has a perovskite crystal structure. Whereas, by using a miscut, it can appear as orthorhombic. In this presentation, we will show the atomic force microscope (AFM) and scanning electron microscope (SEM) results of YBCO grown on substrates with various miscut angles. The surface properties from AFM and SEM will be compared with the ones in the literature. In addition, to determine the YBCO crystal quality, we implement X-ray diffraction (XRD) and rocking curve full width at half maximum measurements in order to investigate and compare the defects such as mosaicity, dislocations, and curvatures of the films. Finally, we will present the electrical transport properties such as resistivity vs temperature and residual resistivity of the miscut films using Van der Pauw method to show the asymmetric conductance in the a-b plane of YBCO.
Adding nanophase defects to YBa2Cu3O7-δ (YBCO) superconductor thin films is well-known to enhance flux pinning, resulting in an increase in current density (Jc). While many previous studies focused on single phase additions, the addition of several phases simultaneously shows promise in improving current density by combining different pinning mechanisms. This paper compares the effect of the addition of two insulating, nonreactive phases of barium zirconium oxide (BZO) and yttrium oxide (Y2O3); both as a single addition of BZO and as a double addition in conjunction with Y2O3. Processing parameters varied the target composition volume percent of BZO from 2-6 vol. %, while maintaining 3 vol. % Y2O3, and the remaining vol. % YBCO. Pulsed laser deposition produced thin films on LaAlO3 (LAO) and SrTiO3 (STO) substrates at various deposition temperatures. Comparison of strong and weak flux pinning mechanisms, current densities, critical temperatures, and microstructures of the resulting films will be presented. The temperature dependence of the current density, Jc(T), will be mathematically modeled to compare the isotropic weak and anisotropic strong pinning contributions.
Understanding the reasons for variations in critical current (Ic) of production coated conductors is becoming increasingly important for magnet builders. To provide such information, we use a reel-to-reel Ic measurement system, YateStar, to characterize the conductors. YateStar is a hybrid device allowing transport Ic measurement in two orthogonal fields and remanent magnetization evaluation of Ic(x), making it much easier to separate vortex pinning and cross-sectional contributions to Ic(x). Regions of interest can be precisely located by Hall probes and then cut out for microstructural studies. Here we show different types of as-manufactured defect populations and cases where no degradation occurs in use and where strong degradation has occurred in use. The applications include magnet coils that have suffered quench damage and cables wound of tapes around a round core. Protection against pre-existing or in situ damage is a significant concern for all magnet builders. Our experiments are providing direct information on these points.
To study the effect of Y2O3 doping on YBCO films under magnetic field. Different content of Y2O3 doped YBCO films are fabricated by self-developed MOCVD. The morphological features of YBCO films were characterized by FESEM. The crystal structure of YBCO film was determined by XRD and Raman. The surface morphology was investigated by AFM.The relationship between the Jc of YBCO films and Y2O3 content is studied. The relationship among Jc, magnetic field and Y2O3 content is carefully studied.
High concentration isotropic artificial pinning centers (APCs) are desirable for high-field applications. In this work, we explore double-doping (DD) of BaZrO3 nanorods (BZO-NRs) and 3 vol.% Y2O3 nanoparticles (Y2O3-NPs) in YBCO as the BZO-NRs concentration is varied in the range of 2-6 vol.%. When comparing with YBCO counterparts with single-doping (SD) of BZO-NRs which shows a monotonic decreasing Jc (H) with BZO doping, an opposite trend of increasing transport critical current density Jc (H) with BZO doping was observed in the DD case. This may be attributed to the considerably promoted BZO-NR splay in the DD case via kinetically impeding the BZO-NR alignment using the second dopant of Y2O3-NPs, which reduces the detrimental strain field overlap in the SD case at high BZO doping. Such a microstructure change is evidenced in the much smaller c-lattice parameter expansion of 0.16% in the DD as opposed to 0.51% in the SD counterparts. In addition, much reduced Tc degradation of 2.2 K in the DD case, in contrast to 5.6 K in the SD case at the same BZO doping levels, illustrates a benefit of the BZO-NR splay. An additional benefit is the enhanced isotropic pinning with respect to the orientation (θ) of the H-field and the enhancement increases with the BZO doping due to the improved Jc at θ away from θ=0 (H//c) by up to 300%. This result suggests that the DD approach is effective in generating strong and isotropic pinning landscape for high-field applications.
Compared with the traditional TFA-MOD methods, the PAFF-MOD method can significantly eliminate the toxicity of fluoride. In addition, the heat treatment process can be simplified and the heat treatment time can be shortened greatly. In this work, a polymer-assisted fluorine-free metal organic deposition (PAFF-MOD) was used to prepare Y2O3-doped YBCO thin film on CeO2-buffered hastelloy. The morphological features of YBCO films were characterized by FESEM. The crystal structure of YBCO film was determined by XRD and Raman. The surface morphology was investigated by AFM.The relationship between the Jc of YBCO films and Y2O3 content is studied. The relationship among Jc, magnetic field and Y2O3 content is carefully studied.
To develop a high winding current density in Bi2Sr2CaCu2Ox (Bi-2212) wires, it is important to use an insulating layer that is thin and fulfills the dielectric requirements. Ideally we would like to use a thin ceramic layer because the other option, braided glass fiber insulation, is about 5 to 10 times thicker and it reacts with the Ag sheath. To date, TiO2 seems to be the most viable ceramic material for a thin insulating layer on Bi-2212 primarily because its sintering temperature is just below the heat treatment temperature of Bi-2212. However, a large recent test coil with only TiO2 insulation suffered from severe electrical shorting after over pressure heat treatment (OPHT). The origin of the shorting was frequent silver “extrusions” through gaps in the TiO2. To understand this unexpected behavior, we investigated the effect of sheath material and hydrostatic pressure with and without the presence of Al2O3 fiber (Nextel-610), used to strengthen the coil. We found that Ag extrusions occur only when Ag-0.2%Mg sheathed wire undergoes OPHT at 50 bar. Ag-0.2%Mg sheathed wires processed at 1 bar and pure Ag sheathed wires processed at 50 bar were free from Ag extrusions. We found no evidence that the Nextel fibers influence extrusions. A key finding is that the Ag extrusions emanating from the Ag-0.2%Mg sheath actually contain no Mg, suggesting that local depletion of Mg facilitates local, heterogeneous deformation under hydrostatic overpressure.
Key words- Bi-2212, TiO2 insulation, Ag extrusion, overpressure processing.
Acknowledgement: This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida and also supported by the US Department of Energy Office of High Energy Physics under grant DE-SC0010421.
Recent increases in the critical current density of Bi2Sr2CaCu2O8-x (Bi-2212) composite wires have driven interest in superconducting magnet applications for this material. However, the round-wire composite material is comprised of brittle filaments in a soft silver matrix, leaving the wire susceptible to filament damage during operation.In this study, Bi-2212 wires were tested on a Walter spring and then imaged to reveal filament damage. Damage events were specified as a function of geometry (flat, concave, and convex wire surfaces), heat treatment condition (1 bar to 100 bar over-pressure processing) and mechanical test condition (tensile or compressive applied strain). After undergoing an external chemical etch process, scanning electron microscopy (SEM) was utilized to analyze the filament damage in each sample. In general, convex surfaces (generated from the Walter spring test) had large amounts and various types of damage compared to the concave surfaces (also from the Walter spring test). Other processing and test conditions are also compared. This new understanding of how damage evolves within Bi-2212 wires allows for better modeling of the wire’s mechanical performance, and influences coil design choices.
Acknowledgments: This work was financially supported by the U.S. Department of Energy (DoE), Office and High Energy Physics (OHEP), award DE-FG02-13ER42036, and benefited from the support of the Materials Science & Engineering Center at UW-Eau Claire. The authors thank Najib Cheggour at the University of Colorado – Boulder for providing electro-mechanical test results.
The microstructures and superconducting properties of the (Bi,Pb)2Sr2Ca2Cu3Ox superconductor (following, Bi,Pb–2223) fabricated by a multilayered precursor and a post-annealing process have been investigated in order to obtain high performance Bi-2223 wires and tapes using two kinds of sputtering targets of nominal compositions of Bi,Pb-2212 and CaCuPbO. We fabricated a alternately layered film as a precursor of Bi,Pb-2223. Alternately layered precursor film was annealed within Bi,Pb-2223 pellets at 840oC for various time. After the annealing, we measured the Tc by resistivity and magnetization measurements. The Tc values by the four probe method reached Tczero = 101 K for the 100 hours annealing.
The as-deposited multilayer film epitaxially grown on a (100) SrTiO3(STO) substrate consisted of 30 nm thickness of Bi-2212 phase and 5-10 nm thickness of Ca-layer and CuO2-layer without BiO and SrO layers. Furthermore, there were large grains of Ca and Cu-rich compositions. After 10 hours annealing, there were heterogeneous microstructure composed of the layered structure of the as–deposited film remained and domains where Bi-2212 phase transformed to Bi-2223 phase. After 100 hours annealing, Bi-2223 domains expanded from interface of the STO substrate to the film surface. However, there were still non-superconducting domains in the Bi-2223 film. The volume fraction of Bi-2223 phase in the superconducting region was approximately 50%. It is a future issue to find the optimum condition to obtain the Bi-2223 single phases.
A Bi2212-based, high temperature superconductor has been developed in reinforced, rectangular wire forms, with up to 400 MPa stress tolerances and useful current densities, making them suitable for application in some coils that are problematic with wide HTS tapes, and that need to operate beyond the field and temperature limits of low temperature superconductors. However, the development of a round wire version has been delayed primarily because of the difficulties in suitably attaching the reinforcement to the curved round wire surfaces. Recently, however we have succeeded in developing, building and qualifying the equipment and tooling for successfully assembling very high modulus, thin reinforcement strips onto nominally 0.8 – 1.2 mm diameter 2212/Ag round wires. With this capability in hand, we are now developing the full process for strong, high Je 2212 round wires, as well as their configurations, including strip dimensions, number of strips, assembly pitches, and with characterization of strip adhesion, wire tensile and bend properties before and after final reaction, and electrical transport properties. As an example, 1.2 mm diameter wire has been produced with addition of 0.1 mm thick reinforcement onto 1 mm diameter 2212/Ag wire, uniformly covering about 80% of its surface and leaving sufficient openings for the required oxygen exchange during final reaction. This wire’s stress tolerance is ~ 400 MPa at the onset of Ic degradation, and its Je in a 5T field at 4.2K is ~ 500 A/mm2 (5T is a current test standard). Bend testing of the diffusion bonded architecture prior to reaction indicates a high degree of formability without damage – to ~ 1 cm diameter, showing great promise for both winding small diameter coils, as well as using the type of cabling approaches that are well developed for producing high current, transposed LTS cables.
The large-scale use of (RE)-Ba-Cu-O bulk superconductors, where RE=Y, Gd, Sm, is in part, limited by their mechanical properties. These materials belong to the ceramic family of compounds and so are inherently brittle. Alloying of (RE)-Ba-Cu-O with silver enables a significant improvement in the mechanical properties, without a detrimental effect upon the superconducting properties. However, the growth of large single grains, as are required for practical applications, is complex and includes many interacting variables. The addition of silver increases the complexity of the manufacturing process further, thus increasing the likelihood of failure of single grain growth.
A critical set of processing variables in the top seeded melt growth process are the times and temperatures in the heating profile which are required to grow single grains. The heating profile contains multiple stages and is influenced by the growth mechanism. The growth rate is important for study of the growth mechanism and enabling determination of a suitable heating profile. However, to date, the growth rate in the YBCO-Ag system has not been reported.
The liquid-phase enrichment technique has significantly increased the reliability with which fully grown single grains of YBCO exhibiting uniform superconducting properties can be produced. This technique has since been adapted to enable the growth of YBCO-Ag bulk samples. In this work we have successfully measured the growth rate of single grains in the YBCO-Ag system the first time. In addition, it has been seen from observation of the shape of the growth front and measurements of the growth rate that the growth process differs significantly between the YBCO and YBCO-Ag systems.
In this work we studied the influence of oxygen doping on the critical fields and temperatures of MgB2 thin films and bulk samples. First, oxygen was intentionally introduced into magnesium diboride (MgB2) films by both ex situ annealing and in situ annealing approaches. Our ex situ annealing technique significantly enhanced the upper critical field (HC2), with the extrapolated critical fields [Hc2(0)] pushed up to near 50T. In parallel, we sought to apply oxygen doping to the MgB2 bulk in the form of pellets. For this part of the work, we prepared two sets of samples one based on an in-situ approach, the other ex-situ. Two doping levels, 5wt % and 10wt % Sn, were added in MgB2 powders, they were pressed into pellets using a load of 1000 psi. Then the ex-situ type samples were heated to 900C in a furnace with Ar flowing. The samples were quenched to room temperature after dwelling on 900C for 50 min. The in-situ approach samples were heated up to 680C in an Ar flowing furnace, dwelled for 2 hours, then they were furnace cooled to room temperature. The magnetization and structure properties were measured and results of the upper critical field of these pellets were compared to the results we obtained from the previous oxygen doped MgB2 films measurements.
Recently interest in the superconducting community has been piqued by superconducting materials that have a non-centrosym-metric crystal structure in which spin singlet or spin triplet states can develop. In this study we investigate the cubic beta-Mn system (T1-xRx)3Al2C (T,R = Mo, Nb, Ta, V, Ti, Cr, Sc) by systematic replacement of the T element of the compound. Of the end member compounds only T = Nb and Mo are known to superconduct at 1.3K and 9.2K respectively. By doping the Mo system we hope to further elucidate these unique pairing states as well as enhance Tc and/or Bc2. The above-named compositions were investigated via magnetic, resistive, and calorimetric analyses. The superconducting phase diagrams of these compounds were then plotted. Comparisons are made between the effects of doping different transition metal elements as well as possible substitutions on the Al and/or C sites.
Magnetism and superconductivity in carbon allotropes are at the center of intense research in physics and material science. Defect-induced magnetism can arise from vacancies or nonmagnetic ad-atoms. Magnetic order can also be induced by ion implantation, such as O, P, S, or B.
We provide here evidence for weak room-temperature ferromagnetism and its possible interfacial coexistence with a small superconducting phase in ion-implanted graphitic samples. The effect of alkanes’ intercalation was also considered. PPMS magneto-transport and magnetization studies were conducted on virgin (diamagnetic) and ion-implanted graphite fibers, highly oriented pyrolytic graphite, graphite foil, and graphene samples for temperatures from 1.9 K to 300 K and magnetic fields up to 9 T.
Sample and temperature dependent, magnetoresistance loops show either anomalous or normal hysteresis. Anomalous hysteresis, as in conventional and high temperature superconductors, is explained on the basis of a two-level critical-state model where pinned fluxons exist inside the Josephson-coupled superconducting grains and also between them. Bulk superconductors with pinned Abrikosov flux lines and ferromagnets show normal hysteresis. The temperature-dependent remanent magnetization has the behavior consistent with excitations of spin waves in a 2D Heisenberg model with weak uniaxial anisotropy. Sharp steps in the remanent magnetization suggest a magneto-structural (martensic) transition with volume change, leading to an antiferromagnetic-ferromagnetic first-order phase transition. Step-like features are due to the coupling of BCS superconductors to inhomogeneous ferromagnetic textures. Imbalance in the defect number for the graphite’s A and B sub-lattices results in the nucleation of ferromagnetic islands within the antiferromagnetic domains. Ferromagnetic M(H) loops and superconducting-like M(H) loops were found in ion-implanted samples. The large magnetocaloric effect associated with a first order phase transition in antiperovskite materials has applications to magnetic refrigeration.
Acknowledgements: The Air Force Office of Scientific Research (AFOSR), The Aerospace Systems Directorate (AFRL/RQ), and United Energy Systems (UES, Inc.)
In recent years Fe-based superconductors have spurred much research due in part to the large number of compounds that have been discovered to exhibit superconductivity and the interesting interplay between magnetism, structure, and the superconducting ground state. In addition, the high Bc2s exhibited by these materials make these compounds interesting for low-temperature, high-field applications. However, recent work has also shown that Tcs of up to 100 K can be achieved in single-layer thin films of this interesting compound. In this poster we detail the AFRL’s attempts at large single crystal synthesis of bulk FeSe. Doping of FeSe single crystals will be attempted so that the fundamental electrical, magnetic, and thermodynamic properties can be discerned, including effects on the superconducting phase diagram (Tc, Bc2, Jc). These data will be intercompared so as to deconvolution of the effects of increasing the interlayer layer spacing via intercalation from the effects of doping.
Cryogenic applications of carbon (C) allotropes such as graphene, highly oriented pyrolytic graphite (HOPG), carbon fibers (CFs), and diamond-like carbon films (DLC) range from CF-enforced high critical temperature superconducting (HTS) wires and tapes for superconducting generators and magnets for fusion reactors, space technology, levitation, or the handling of liquefied gases in cryocoolers. C-based materials combine lightness with excellent thermal, electrical, and mechanical (strength) properties. Proximity-induced superconductivity and engineered ferromagnetism in C allotropes find applications to hetero-structures for enhanced flux pinning or spintronics. Therefore, knowledge of C allotropes' properties is important for their choice of applications.
Herein we present results on magneto-transport properties of CFs, carbon nanotubes, HOPG, as well as amorphous C and DLCs. With the sample in the four-wire arrangement, magneto-resistance data at cryogenic temperatures from 1.9 K or 5 K to 300 K was obtained using the Quantum Design Physical Properties Measurement System. Ion implantation and intercalation produced noticeable changes on the electrical properties, such as electrical resistivity and current carrying capacity. We have found temperature or/and magnetic-field driven insulator-metal-insulator transitions of quantum nature. Just like Bi, graphite has Bose metallic states in which both superconducting and excitonic correlations play a role. The latter become evident in the case of CFs, where both superconducting fluctuations and antiferromagnetic correlations become important at low temperatures. The two-band conduction in HOPG has a thermal activation term explained by others as due to the existence of narrow superconducting channels in which thermal fluctuations can cause phase slips. In addition, observation of giant magnetoresistance suggests the magnetocaloric effect.
Acknowledgements: The Air Force Office of Scientific Research (AFOSR), The Aerospace Systems Directorate (AFRL/RQ), and United Energy Systems (UES, Inc.)
Recent theoretical predictions have suggested that the band structure of BaCr2As2 is similar to the parent BaFe2As2 phase in such a way that doping that compresses the lattice and/or donates electrons to the may induce a superconducting ground state. We at AFRL have successfully grown both the parent phase BaCr2As2 compound and its doped daughters in single crystal form. These doped materials were characterized in terms of their fundamental magnetic, electrical, structural, and thermodynamic properties in a search for superconductivity. Correlations were made between these properties. Synchrotron and/or neutron diffraction was used to map structural and/or magnetic phase transitions. Finally, density functional theory is used to explain the properties we measure in terms of the electronic structure of the material and its evolution with doping.
In order to cover the required cryogenic load, several cryogenic groups, e.g. at CERN, ITER, JLab, SLAC, have to install several refrigerators with maximal power capacities each. As an alternative, development of larger refrigerators up to 120kW power could be an alternative to the installation of several “small” ones. In the present paper, the novel concept of 60÷120 kW refrigerator is considered. The discussion of novel concept will be preceded by discussion of basic design of current “state-of-the-art” refrigerators/liquefiers as well as advanced ones using high efficient heat exchangers and turbines with expected overall thermodynamic efficiencies up to 35%. In the first part, the general layout, screw/turbo compressor stations as well as 80-300K box will be presented. In the second part, the 4-80K box is considered.
Following the update of the European strategy in particle physics, CERN has undertaken an international study of possible future circular colliders beyond the LHC. The study considers several options for very high-energy hadron-hadron, electron-positron and hadron-electron colliders. From the cryogenics point of view, the most challenging option is the hadron-hadron collider (FCC-hh) for which the conceptual design of the cryogenic system is progressing. The FCC-hh cryogenic system will have to produce up to 120 kW at 1.8 K for the superconducting magnet cooling, 6 MW between 40 and 60 K for the beam-screen and thermal-shield cooling as well as 850 g/s between 40 and 300 K for the HTS current-lead cooling. The corresponding total entropic load represents about 1 MW equivalent at 4.5 K and this cryogenic system will be by far the largest ever designed. In addition, the total mass to be cooled down is about 250’000 t and an innovative cool-down process must be proposed.
This paper will present the proposed cryogenic layout and architecture, the cooling principles of the main components, the corresponding cooling schemes, as well as the cryogenic plant arrangement and proposed process cycles. The corresponding required development plan for such challenging cryogenic system will be highlighted.
After the successful Run 1 (2010-2012), the LHC entered its first Long Shutdown period (LS1, 2013-2014). During LS1 the LHC cryogenic system went under a complete maintenance and consolidation program. The LHC resumed operation in 2015 with an increased beam energy from 4 TeV to 6.5 TeV. Prior to the new physics Run 2 (2015-2018), the LHC was progressively cooled down from ambient to the 1.9 K operation temperature.
The LHC has resumed operation with beams in April 2015. Operational margins on the cryogenic capacity were reduced compared to Run 1, mainly due to the observed higher than expected electron-cloud heat load coming from increased beam energy and intensity. Maintaining and improving the cryogenic availability level required the implementation of a series of actions in order to deal with the observed heat loads.
This paper describes the results from the process optimization and update of the control system, thus allowing the adjustment of the non-isothermal heat load at 4.5 – 20 K and the optimized dynamic behaviour of the cryogenic system versus the electron-cloud thermal load. Effects from the new regulation settings applied for operation on the electrical distribution feed-boxes and inner triplets will be discussed. The efficiency of the preventive and corrective maintenance, as well as the benefits and issues of the present cryogenic system configuration for Run 2 operational scenario will be described. Finally, the overall availability results and helium management of the LHC cryogenic system during the 2015-2016 operational period will be presented.
The cryogenic system of the LHC will be upgraded by 2025 to comply with a considerable increase of beam induced heat loads deriving from higher beam currents and peak luminosity levels from the High-Luminosity LHC. The current baseline foresees a modified sectorization scheme with three additional cryogenic plants dedicated to cool the insertions at LHC’s points 1, 4 and 5, reducing the refrigeration duty of the existent adjacent plants.
This paper assesses the refrigeration duty of the eight existing plants considering the modified sectorization and increased heat load deposition. The accelerator loads and distribution losses are quantified for each plant and compared to the existing refrigeration capacity. The heat load values were obtained from the extrapolation of previous LHC assessments as well as from new calculations. Specifically for the LHC point 4 cryogenic equipment, based on updated refrigeration requirements, the upgrade of an existing plant is proposed as an alternative to the baseline scenario.
Commissioning the XFEL cryogenic system has begun in the middle of 2015 by putting into operation components necessary for operating the XFEL injector. The injector was cooled down to 2K at the end of 2015 and operated - including beam commissioning - until August 2016. After warming up of the whole XFEL cryogenic system, commissioning remaining components including the 1.5 km long superconducting XFEL linear accelerator (linac) has commenced and was completed in beginning of December 2016. After conclusive pressure and leak tests, and flushing the cool-down has started on 11 December 2016. Stable 4.5K operation both for the linac and injector was established on 27 December.
In this paper the XFEL cryogenic system is introduced. The cool-down sequences are described and the measured cool-down evolution is presented. Thermal losses of single circuits are given. Preliminary conclusions with the review of critical points are drawn.
The RF operation of the about 800 superconducting 1.3GHz 9-cell cavities of the XFEL linac requires helium II bath cooling at 2K, corresponding to a vapor pressure of 3100 Pa. After the first cool-down of the XFEL linac to 4K in December, 27th,2016 the operation of the 2K cryogenic system was started in January, 2th 2017. The 2K cryogenic system consist of a 4-stage set of cold compressors to compress helium vapor at a mass flow of up to 100 g/s from 2400 Pa to about 100kPa and a full flow bypass with an arrangement of heat exchangers and control valves.
This paper describes the XFEL refrigerating plant, especially the 2K cryogenic system, the tuning of the cold compressor regulation to adapt to the XFEL linac static and dynamic heat loads and experience of about 6 months of operation.
Cryogenic temperature sensors are used in high energy particle colliders to monitor the temperatures of superconducting magnets, superconducting RF cavities, and cryogen infrastructure. While not intentional, these components are irradiated by leakage radiation during operation of the collider. A common type of cryogenic thermometer used in these applications is the CernoxTM resistance thermometer (CxRT) manufactured by Lake Shore Cryotronics, Inc. This work examines the radiation-induced calibration offsets on CxRT models CX-1050-SD-HT and CX-1080-SD-HT resulting from exposure to very high levels of gamma radiation. Samples from two different wafers of each of these two models tested were subjected to a gamma radiation dose ranging from 10 kGy to 5,000 kGy. The data was analyzed in terms of the temperature-equivalent resistance change between pre- and post-irradiation calibrations. The data shows that the resistance of these devices decreased following irradiation resulting in positive temperature offsets across the 1.4 K to 330 K temperature range. Variations in response were observed between wafers of the same CxRT model. Overall, the offsets increased with increasing temperature and increasing gamma radiation dose. At 1.4 K the average offsets ranged from 0 mK to +15 mK in going from a 10 kGy to a 5,000 kGy exposure. At 300 K the average offsets ranged from +175 mK to +2,500 mK in going from a 10 kGy to a 5,000 kGy exposure. Equivalent temperature offset data are presented over the 1.4 K to 330 K temperature range by CxRT model, wafer, and total gamma dose.
The Karlsruhe Institute of Technology (KIT) and the WEKA AG jointly develop a commercial flowmeter for application in helium cryostats. The flowmeter works according to a new thermal measurement principle, which eliminates all systematic uncertainties and enables self-calibration during real operation. Ideally, the resulting uncertainty of the measured flowrate is only dependent on signal noises, which are typically very small with regard to the measured value. Under real operating conditions, cryoplant-dependent flowrate fluctuations induce an additional uncertainty, which follows from the sensitivity of the method. This paper presents experimental results with helium at temperatures between 30 and 70 K and flowrates in the range of 4 to 12 g/s. The experiments were carried out in a control cryostat of the 2 kW helium refrigerator of the TOSKA test facility at KIT. Inside the cryostat, the new flowmeter was installed in series to a Venturi tube that was used for reference measurements. The self-calibration capability during real cryoplant operation has been demonstrated by the measurements. The influences of temperature and flowrate fluctuations on the self-calibration uncertainty are discussed.
The upcoming generation of accelerators demands for the design and installation of Superconducting Radiofrequency (SRF) cavities of different sizes and geometries. Many of these SRF cavities are based on bulk Nb in a He-II bath. The individual testing of these devices is necessary to identify eventual surface defects that could induce a quench during operation. A versatile way of adapting these tests to different cavities is non-contact thermometry. Making use of the second sound propagation in He-II, a hot spot on the cavity can be localized by trilateration. Metallurgic inspection can be performed on the identified area to investigate the limited performance of the material. So far, non-contact thermometry has been mainly based on Oscillating Superleak Transducers, an oscillating membrane detector sensitive to changes in the normal to superfluid component ratio in He-II. To improve the method, better space resolution and a more purely thermometric information of the second sound wave could be beneficial. This is the reason why Transitions Edge Sensors (TES) are being developed. TES are based on the superconducting (SC) transition of a thin film in the He-II temperature range. TES sense the huge electrical resistivity change of the film as a function of temperature for a given current density in a very narrow temperature range. In this work, a TES fabrication method has been conceived using state-of-the-art photolithography techniques obtaining sensors of less than 1 mm2 typical size. Different choices of materials (substrate and thin film composition) and sensor geometry have been characterized in the SC transition, verifying the capability of these sensors to detect with good signal-to-noise ratio a second sound event. Subsequently, a robust camera-like device with a network of many sensors at different positions has been created in order to provide a compact element that allows trilateration of quench hotspots.
Helium cryogenic systems are extensively used at CERN under several configurations for CERN accelerators and detectors. The Warm Compressor Station (WCS) is the primary component of the helium cryogenic systems. The basic controls structure mainly depends on the bypass, charge and discharge valves configuration ensuring the nominal flow and compression ratio. This paper presents three studied methods for the WCS process control systems covering all transient and operational requirements: the PI(D) Control approach, the Fuzzy Logic Control approach (FLC) and the Internal Model Control approach (IMC). The paper emphasises on simulation results of the different control strategies using Ecosimpro software associated to the CERN CryoLib library. Advantages and limitations of each method are presented.
Industrial process controllers for cryogenic systems used in test facilities for superconducting magnets are typically PIDs, tuned by operational expertise according to users requirements (covering cryogenic transients and associated thermo-mechanical constraints). In this paper, an alternative fully-automatic solution, equally based on PID controllers, is proposed. Following comparison of the operational expertise and alternative fully-automatic approaches, a new process control configuration, based on an estimated multiple-input/multiple-output (MIMO) model is proposed. The new MIMO model-based approach fulfils the required operational constraints while improving performance compared to existing solutions.
The analysis and design work is carried out using both theoretical and numerical tools and is validated on the case study of the High Field Magnet (HFM) cryogenic test bench running at the SM18 test facility located at CERN. The proposed solution was validated by simulation using the CERN ECOSIMPRO software tools using the cryogenic library (CRYOLIB) developed at CERN.
Due to its low viscosity, cryogenic He II has potential use for simulating large-scale, high Reynolds number turbulent flow in a compact and efficient apparatus. To realize this potential, the behavior of the fluid in the simplest cases, such as turbulence generated by flow past a mesh grid, must be well understood. We have designed, constructed, and commissioned an apparatus to visualize the evolution of turbulence in the wake of a mesh grid towed through He II. Visualization is accomplished using the particle tracking velocimetry (PTV) technique, where µm-sized tracer particles are introduced to the flow, illuminated with a planar laser sheet, and recorded by a scientific imaging camera; the particles move with the fluid, and tracking their motion with a computer algorithm results in a complete map of the turbulent velocity field in the imaging region. In our experiment, this region is inside a carefully designed He II filled cast acrylic channel measuring approximately 16 x 16 x 330 mm. One of three different grids, which have mesh numbers M = 3, 3.75, or 5 mm, can be attached to the pulling system which moves it through the channel with constant velocity up to 500 mm/s. The consequent motion of the solidified deuterium tracer particles is used to investigate the energy statistics, effective kinematic viscosity, and quantized vortex dynamics in turbulent He II.
The magnets for the next step in accelerator physics, such as the High Luminosity upgrade of the LHC (HL- LHC) and the Future Circular Collider (FCC), require the development of new technologies for manufacturing and monitoring. To meet the HL-LHC new requirements, a large upgrade of the CERN SM18 cryogenic test facilities is ongoing with the implementation of new cryostats and cryogenic instrumentation.
The paper deals with the advances in the development and the calibration of fiber optic sensors (FOS) in the range 300 – 4 K using a dedicated closed-cycle refrigerator system composed of a pulse tube and a cryogen-free cryostat. The calibrated FOS have been installed in three vertical cryostats used for testing superconducting magnets down to 1.9 K or 4.2 K and in the variable temperature test bench (100 - 4.2 K). The dedicated 20-m-long cryostat for testing the MgB2 superconducting link (10 - 30 K) has also been equipped.
In this paper, some examples of FOS measurements of cryostat temperature evolution are presented as well as measurements of strain and temperature performed on several Nb3Sn and High Temperature Superconducting magnets during their powering tests. Results and experiences on the use of FOS for cryogenics applications are discussed in more details to assess the reliability of the method.
Digital image correlation (DIC) is a non-contact optical method for in-plane displacement and strain measurement, which has been widely accepted and applied in mechanical property analysis owing to its simple experimental steps, high accuracy and large range of measurement. However, it has been rarely used in cryogenic mechanical test since the opaque design of cryostats as well as interaction of optics with liquid coolants such as liquid nitrogen or liquid helium. In the present work, a coolant-free cryogenic mechanical property test system cooled by G-M cryocoolers, with a continuous, tunable environmental temperature from room temperature down to 2.7 K, was developed and tested. Two optical windows with a diameter of 100 mm made of quartz, which are compatible with the DIC technology, were designed on the cryostat and sample chamber. Surface displacement and crack-tip strain field of 316LN austenitic stainless steel were studied at 4 K by using this system. The results indicate that the test system with DIC technology can satisfy well for mechanical analysis of material at cryogenic temperatures.
Numerical simulations of superfluid helium are necessary to design the next generation of superconducting accelerator magnets. Previous studies have presented the thermodynamic equations implemented in the Fluent CFD software to model the thermal behavior of superfluid helium. Momentum and energy equations have been modified in the solver to model a simplified two-fluid model. In this model, the thermo-mechanical effect term and the Gorter-Mellink mutual friction term are the dominant terms in the momentum equation for the superfluid component. This assumption is valid for most of superfluid applications. Transient thermal and dynamic behavior of superfluid helium has been studied in this paper. The equivalent thermal conductivity in the energy equation is represented by the Gorter-Mellink term and both the Theoretical and the Sato formulation of this term have been compared to unsteady helium superfluid experiments. The main difference between these two formulations is the coefficient to the power of the temperature gradient between the hot and the cold part in the equivalent thermal conductivity. Furthermore, the impact of the Kapitza thermal resistance at the surface of the heater and the initial condition in the fluid has also been numerically quantified. The results of these unsteady simulations have been compared with two experiments. The first one is a Van Sciver experiment on a 10 m long, and 9 mm diameter tube at saturation conditions and the other, realized in our laboratory, is a 150x50x10 mm rectangular canal filled with pressurized superfluid helium. Both studies have been performed with a heating source that starts delivering power at the beginning of the experiment and many temperature sensors measure the transient thermal behavior of the superfluid helium at different locations.
The cryogenic systems of large scientific facilities using superfluid helium technologies (e.g. LHC, SNS, CEFAB, XFEL, ESS and LCLS-II) include a cold helium circuit composed of a subcooled liquid helium supply line and a low-pressure return line. In nominal operation conditions these lines together with heat exchangers and throttling valves form a Joul-Thomson open cycle. Due to long distances between the cryogenic plant and cryogenic users the line lengths can reach hundreds or even thousands meters. Usually the low-pressure return line is a large size pipe, which inner diameter can exceed 300 mm in order to fulfill a strict pressure drop requirement.
In some cases (e.g. LHC and LCLS-II) the accelerators and also the cold helium circuit lines are slanted up or down from a horizontal line even up to a couple of degrees. Such slopes do not disturb significantly the sub-atmospheric helium flows in the lines at nominal operation conditions. However, in some transient modes, especially during the sequential fast cool-down of cryomodules, there is a risk of a counter flow in the low-pressure return line. This counter flow phenomenon can be driven mainly by free convection and it can disturb the cool down dynamics or even affect the performance characteristic of some cryogenic devices, which are sensitive to cool down rates and temperature gradients.
The paper presents the numerical analysis of free convection in cold helium vapor flows in a long straight and sloped line. The methodology of numerical modeling of the thermo-hydraulic phenomena is described in details. The results of the numerical simulations performed for various pipe lengths, slopes and mass flow rates are compiled and thoroughly discussed.
Concurrent pressure drop and cooling of a super-critical or sub-cooled liquid stream can have the same effect as adiabatic expansion even though there is no work extraction. A practical implementation is as straight forward as counter-flow heat exchange with a colder fluid. The concurrent pressure drop need not be continuous within respect to the heat exchange, but may occur in a step-wise manner, in between heat exchange. Two aspects of this effect of pressure drop with heat transfer are examined; a thermodynamic and a practical process equivalent isentropic expansion efficiency. This real fluid phenomenon is useful to understand in applications where work extraction is either not practical or has not been developed. A super-critical helium supply, often around 3 bar and 4.5 K, being ultimately used as a superfluid (usually around 1.8 to 2.1 K) to cool a Niobium superconducting radio frequency cavity or a superconducting magnet is one such particular application. This paper examines the thermodynamic nature of this phenomenon.
Oxygen is paramagnetic so is subjected to bulk forces under inhomogeneous magnetic field and its paramagnetism is greatly enhanced under low temperatures. Cryogenic distillation is one of the main methods for air separation, which is a potential application for the paramagnetism of oxygen. During distillation, gaseous mixtures rise from the bottom of the column and penetrate through layers of liquids on the distillation trays, main component of which is the liquid oxygen. When applied with magnetic field, bubble shapes and behaviors will change due to susceptibility contrast between liquid and vapor but knowledge about bubble shape and dynamics during this process is yet incomplete. In this study, influences of magnetic forces on shapes and behaviors of bubbles in liquid oxygen are investigated at different positions of the vertically axisymmetric magnetic field through finite element analysis. Level set method is used to capture the moving two-phase boundaries, coupled with magnetic field based on Ampere’s law. The results show that bubbles can be spherical or elongated vertically or horizontally when it is static and the elongation ratio u depends on the bubble volume and position in the magnetic field. The corresponding results are compared with other experimental studies to assess the ability of the numerical model to predict bubble shape and dynamics in a moving situation. By this multiphysical model, bubble shape and behaviors during rising process are then studied. It is found that magnetic field provides the energy in shaping the bubbles except of surface tension and gravity.
Storage of cryogenic liquids is a critical issue in many cryogenic applications. These liquids tend to boil off easily. The resulting evaporative loss may be minimized by subcooling the liquid. Such a technique has been applied in space launch vehicles for storage of liquid oxygen. A liquid may be subcooled by bubbling a near immiscible unsaturated gas through the liquid. Subcooling results from the evaporation of liquid into the gas bubble. The liquid evaporates due to a difference between the saturation pressure of the liquid and partial pressure of the liquid component inside the gas bubble. Liquid evaporation, hence the subcooling stops when the two pressures equalize. The rate and degree of subcooling depend on the bubble dynamics (coalescence, breakup, deformation etc.) as this dictate the heat and mass transfer between the gas bubble and the liquid. Therefore, the operating conditions such as gas flow rate, gas injection temperature, and system configuration have profound effects on liquid subcooling. However, due to a scarcity of literature on liquid subcooling by gas bubbling, a proper understanding of the process performance is lacking. The present study aims at capturing the bubble dynamics effect on the injection cooling in a lumped parameter frame. This approach is effective in gauging the significance of various process variables on the liquid storability by injection cooling. Thus this method can help in designing and rating an injection cooling system.
REBCO coated conductors (REBCO-CC) have attractive features such as high {\it I}{c} performances even in the magnetic fields. As the applications which can effectively use the features, “electric propulsion transportation” is considered to be strong candidate. In the system, several superconducting devices can be applied such as “Generator”, “Motor” and “Cable”. If all superconducting rotating machine can be realized, the advantages in generator and motor should be stronger. In order to actualize the superconducting transportation system, the REBCO-CC with high-performances such as high Ic in both self-field & external field and low ac-loss has to be prepared. Additionally, low cost CC is always desired. In this paper, the present status of CC in Japan is reviewed for the electric propulsion transportation.
Concerning an improvement of in-field performance, APC-introduction has been known to be valid. In the PLD process, it was found that the material combination of EuBCO and BaHfO{3} is more effective to obtain high Ic in the magnetic field. It revealed high performance in wide ranges of temperature and magnetic field. As a typical value, the high {\it I}{c} ({\it B}) value of 569 A/cm-w under 3T({\it B}//c) at 65 K. On the other hand, the break-through was taken place in R&D of TFA-MOD process, which is known as a cost effective process. The in-field {\it J}{c} value was remarkably improved by thinning once coat-thickness in the MOD process. Additionally, the scribing technique has been developed to make filament-structure in the coated conductors to reduce ac-losses. An ac-loss reduction even in the 100 m long tapes was actually confirmed. Furthermore, the validity could be maintained even in the coil shale. It should lead to realization of low loss armature coil in the all superconducting rotating machines.
This work has been supported by METI, NEDO, AMED and AIST.
As high-temperature superconductors – in particular REBCO-based coated conductors – begin to find their way into mainstream applications and application prototypes, intended to compete on economic terms with conventional technologies, the need for targeted characterization of the as-yet immature, varied and constantly evolving wire component becomes increasingly important. In this talk, on the basis of the Robinson Institute’s characterization for a variety of purposes of a range of contemporary high-temperature superconducting wires produced by different manufacturers, both established and emerging, I will evidence the severe detriments to efficient device design that can result from making assumptions based on a limited dataset regarding the relative performance of differently architectured wires across broad regimes of temperature and magnetic field. I will demonstrate how only a detailed characterization under the precise operating conditions of relevance to the particular final application can adequately inform materials selection in the event that the optimal design efficiency is to be achieved. Examples will be shown where the use of detailed, specific performance data at the design stage provided a substantial, measurable improvement in modelled device performance compared to the use of a sparse or generic dataset. This is then shown to correspond to a significant operating temperature buffer post-build, providing the potential for an equivalent reduction in wire quantity required (and associated cost reduction) at the design stage. As design targets become increasingly unforgiving of drastic over-engineering in the move from proof-of-principle to cost-competitive implementation, such detailed performance information on the underlying wire technology becomes an essential prerequisite to the successful realization of project targets.
Superconducting cable is expected to be a device to go in a market in near future. As for the applications meet the needs and cost point of view, we selected a high capacity bus connecting between a generator and a step-up transformer in power plant, where an isolated phase bus (IPB) is used for the conventional technology. 2015, we designed a HTS superconducting bus with rated 22kV and 10kA. Basic studies were performed, such as Ic measurement test of each phase and withstand voltage test thereof, resulting in indicating effectiveness of replacement of IPB with superconducting bus with triaxial cable. In this study, based on the specification designed in 2015, we prepared prototype cables having the currying capacity of 1/4 and tested them using the test parameter of IPB. We used in-house YBCO superconducting tapes manufactured by MOD process, which have 4155m in length, 4mm in width, and the Ic values around 150A at 77.3K in self-field. A 20m-long test triaxial bus was manufactured to confirm the electrical and mechanical properties. We performed type test with triaxial bus based on CIGRE TB 538. After loading cycle test we confirmed that test circuit was withstood for AC 52kV and lightning impulse voltage 125kV and partial discharge was not occur over noise level. We also performed 3 phase short-circuit current test on 2.5m sample of triaxial bus applied 25kV with duration 2.0 sec. Sample of triaxial bus could flow such 3 phase short-circuit current without electrical and mechanical damage. In this presentation, we will report those results of a 1/4 scale of superconducting triaxial bus. This works is available for application in the large fields such as electric propulsion
aircrafts. Acknowledgment This paper is based on results obtained from a project subsidized by the New Energy and Industrial Technology Development Organization (NEDO).
In 2011 the European Commission presented a report in which Europe’s vision for the aviation sector in 2050 is manifested. [1] Amongst others, “Flightpath 2050” set goals for the reduction of the carbon footprint of the aviation sector. Compared to the capabilities of typical new aircraft in the year 2000 CO2 and NOx emissions per passenger kilometer shall be reduced by 75% and 90%, respectively. When taxiing aircraft movements are even supposed to be emissions-free. Another goal is the reduction of noise emissions of a flying aircraft by 65%.
These ambitious goals can only be achieved by innovative propulsion systems and aircraft architectures. Electric and hybrid-electric propulsion systems would allow distributed propulsion by separating power and thrust generation. Even though electric or hybrid-electric propulsion systems are already used in cars, ships and big mining trucks, for example, the challenges for the aviation sector are huge. Weight and size issues play a major role for the design and the efficiency needs to be as high is possible. Highly efficient and lightweight superconducting components could help to achieve the ambitious goals of the aviation sector.
In the framework of the German TELOS-Project, we investigate the feasibility of a High-Temperature Superconducting (HTS) power distribution system for hybrid-electric aircraft propulsion systems and develop a demonstrator cable for DC power distribution. In this paper we discuss different design aspects for the cable and its cryogenic system. Current-lead design, cable-joints and bendability of the cable are important issues and first results of calculations and experiments related to these issues will be presented.
[1] “Flightpath 2050 Europe’s Vision for Aviation” Report of the High Level Group on Aviation Research, doi: 10.2777/5026
Next generation electric power systems require higher capacity, efficiency, and stability to meet the demands of increasingly complicated grid systems. High-temperature superconductors (HTS) provide unique solutions to stringent operating requirements, including the ability to protect electric power apparatus and systems from large currents that can develop during a fault. The extensive development of Conductor on Round Core (CORC®) cables and wires has resulted in round, multifilament, REBCO conductors with critical current densities beyond 200 Amm-2 at 77 K. The inherent fault current limiting capabilities of a short kA-class CORC® wire of less than 4 mm thickness are demonstrated in liquid nitrogen, developing nearly instantaneous voltages in excess of 20 V/m that increased to about 70 V/m within 15 ms of applied overcurrents up to 250 % of the critical current. Enhanced current sharing between tapes enabled by the CORC® cable topology appears to mitigate the issue of hot-spots caused by in homogeneities on the HTS tape level by providing several alternate superconducting routes for current to bypass low Ic sections of the tapes. Operation of the CORC® FCL conductor in stand-alone operation and operated as part of a hybrid-cable system, in which the overcurrent is redirected to a normal conducting path outside of the cryogenic environment, are demonstrated without any degradation of the CORC® wire performance. The results show that highly flexible CORC® wires with record current densities are able to function as fault current limiters in which they develop record voltages per unit length of any HTS FCL cable without the need for resistive laminates.
Acknowledgement
This work was supported by the US Navy under agreement number N00024-16-P-4071.
Hyper Tech Research will report on progress that has been made on developing magnesium diboride superconductor wires, coils and magnets for commercialization efforts, with a specific emphasis on conduction cooled MRI and AC motor/generator applications.
100 m long 6-filament MgB2 wire was successfully fabricated using internal magnesium diffusion (IMD) process [1]. We investigated the transport properties and the uniformity of this long multifilament IMD wire. The MgB2 layer and the sub-filament region are regular, and the Jc values have a fairly homogenous distribution throughout the wire, suggesting that there were no obvious defects along the length of the wire. A layer Jc as high as 1.2×10^5 A/cm2 at 4.2 K and 8 T was obtained, which was comparable to the highest value of the long multifilament IMD wire reported so far.
We also made and tested two IMD-processed MgB2 solenoid coils using 26 m long 6-filament wires. The coils were prepared by using a wind-and-react method and cooled by liquid helium. The coil Ic values measured at 4.2 K are almost equal to the estimated Ic values of short length wire, suggesting that the long multi-filamentary wire has sufficient longitudinal homogeneity. These results indicate that the long multifilament IMD-processed MgB2 superconducting wire is suitable for practical applications.
[1] Dongliang Wang, Da Xu, Xianping Zhang, Chao Yao, Pusheng Yuan, Yanwei Ma, Hidetoshi Oguro, Satoshi Awaji, Kazuo Watanabe, Uniform transport performance of a 100 m-class multifilament MgB2 wire fabricated by an internal Mg diffusion process, Supercond. Sci. Technol., 2016, 29(6):065003.
It has been found that Dy2O3 doping can enhance critical current density Jc, especially at high temperature (10 K to 30 K), without changing the transition temperature Tc or upper critical magnetic field Bc2 of MgB2. However, it is interestingly noted that the irreversibility field µ0Hirr of the MgB2 sample was increased by Dy2O3 doping. In this paper, the mechanism of the Dy2O3 doping on the MgB2 wire was further studied. A series of carbon and Dy2O3 co-doped MgB2 wires were fabricated. The carbon concentrations of these wires were fixed at 2.0 wt. % and the Dy2O3 concentrations ranged from 2.0 wt. % through 4.0 wt. % to 6.0 wt. %. The heat treatment conditions were 675 °C/30 min, 675 °C/60 min, and 675 °C/120 min. The transport critical current density of the co-doped MgB2 wire was doubled at 20 K, which suggests a reduction in the anisotropy of the critical magnetic field induced by Dy2O3 doping. The specific heats of the MgB2 wires were measured to investigate the anisotropy of the critical magnetic field of the MgB2 wires. The field dependence of the critical current densities of the MgB2 wires was measured at 4.2 K to 30 K. The variation in the resistivity of the MgB2 wires with temperature was measured by using four-point method to study the impurity scattering and grain connectivity of the MgB2 sample. The transverse cross sectional areas of the MgB2 wires were observed by scanning electron microscope (SEM).
As indicated by SEM and Auger analysis, a sizeable amount of oxygen is usually present in superconducting MgB2-based materials (bulks, thin films, and wires). The established correlations between the characteristics of MgB2-based superconducting materials and their structural features, in particular the oxygen distribution and content are under the consideration. The matrix phase of bulk MgB2 contains rather small amounts of oxygen, but a high amount of close to MgBO dispersed inclusions or regions. X-ray phase analysis with Rietveld refinement of several highly dense MgB2-based (with high Jc) bulk samples (even that prepared under special conditions for preventing oxygenation) showed that the superconducting phase had a composition MgB1.68-1.8O0.2-0.32 instead of pure MgB2. Besides, a small amount of a phase with MgO structure was observed in the materials by x-rays. The calculation of the enthalpy of formation and Gibbs energy confirms the possibility of oxygen solubility in MgB2 and shows that the formation of MgB1.75O0.25 is most favorable. The results of ab initio calculations of the electronic structure and stability of the MgB2 compounds with partial oxygen substitution for boron show that it is energetically preferable for oxygen atoms to replace boron pairwise or form chains. In the case of MgB1.75O0.25 it is preferable oxygen incorporation into each second boron plane and thus the undisturbed boron plane is alternated by the boron plane with oxygen atoms. The experimental TEM study gave support for these calculations.
The numerical calculations in the DFT approximation showed that in the case of substitution of boron atoms to carbon the energetically preferable is their homogeneous distribution. The small amount of the carbon atoms in MgB2 structure can dramatically affect the superconducting characteristics because it will lead to the essential changes in the electron density distribution.
Persistent joints using in-situ multifilamentary MgB2 wires have been developed. The joints were made using MRI style MgB2 wire. In order to test a joint, the wire was wound into a one turn coil and then connected by the place outside and away from the single turn coil. A hall sensor was placed in the coil to measure the field of the single turn as well as the decay of that field. After preparation, such samples would be cooled, a persistent current would be induced by a superconducting magnet into which the coil was placed, and its decay measured. These measurements were performed at 4.2 K as a function of a background field. A heater wire was also used to heat the wire and show the sudden drop of the persistent current to quantify the amount of current. Various joints were tested, typical results were 200-300 A of persistent current at self-field, 4 K, and resistance values of 5 x 10-12 . Substantial persistent currents were present up to 4 T with similar resistance values. The application to MgB2 MRI systems is discussed.
The formation of the AIMI MgB2 wire is based on the infiltration of Mg into B powder layer at 650 °C to 675 °C. This study focused on the effect of oxide dopants on the MgB2 phase formation during the diffusion of Mg into the B powder layer. In Dy2O3 doped MgB2 AIMI wires, Dy2O3 reacted with melting Mg to form DyB4 and MgO during heat treatment. The unreacted Dy2O3, DyB4 and MgO have the potential to work as flux pinning centers or to refine MgB2 grain size in the AIMI wires. X-ray powder diffraction (XRD) was used to analyze the formation of the major impurity phases in the MgB2 wires. The plot of pinning force versus magnetic field was obtained to indicate the flux pinning mechanisms of the Dy2O3 doped MgB2 AIMI wires. On the other hand, the influence of Dy2O3 on the Mg infiltration depth was studied. The MgB2 area fraction of Dy2O3 doped MgB2 AIMI wires were compared with that of undoped MgB2 AIMI wires under same heat treatment condition. The transverse cross sectional areas of the MgB2 wires were observed by scanning electron microscope (SEM).
Maraging steels are low carbon, high Ni steels that have an extraordinary combination of high strength, and fracture toughness at room temperature. These steels could be attractive for cryogenic structural fatigue applications with cycle requirements between hundred thousand and a million cycles, however, there is a paucity of cryogenic test data of these steels. Preliminary examinations reveal that at 77K, this alloy can operate at a cyclic stress value of 1000 MPa (r=0.1), for greater than 106 cycles. Here, we report on mechanical testing and axial fatigue life data (S-n curves) on commercially available C-250 maraging steel at cryogenic temperatures including 77K, and 4K testing. In view of application in cryogenic applications notch sensitivity issues will also be presented. Metallographic evaluations of microstructure, and fracture surfaces will be presented to correlate structure-property relationships.
The main aim of this paper is to evaluate the mechanical properties and microstructure of 316LN high-nitrogen austenitic stainless steel after rolling under ambient and cryogenic conditions. Cryorolling was realized after cooling in liquid nitrogen bath at 77 K. During the rolling at ambient temperature (TA) can take place the dynamic recovery of the microstructure. This is strongly retarded by rolling under cryogenic conditions (TC). The main plastic deformation mechanism at ambient temperatures is slip. When the temperature is decreased to cryogenic level and the strain is increased, scanning electron microscope analysis showed the slip is accompanied by deformation bands and twins. In this case, stored energy also increases. For thermal analysis differential scanning calorimetry was carried out.
Samples were tested by tensile test according to the standards at three different temperatures: TT = <4.2; 293> [K]. Total deformation after rolling was in the range ε = <10; 50> [%]. The values of the mechanical properties are YS = <524; 1870> [MPa], UTS = <715; 2118> [MPa], depending on the rolling and testing temperatures. Generally, the total elongation decreased with increasing total deformation and decreasing testing temperature. The values of elongation for TA after deformation ε = <10; 50> [%] and TT = <4,2; 77; 293> [K] are in the range A5 = <1.5; 46> [%]. For TC and the same deformations and temperatures ranges, A5 = <3.7; 43> [%].
In response to the ever increasing requirements for all materials that are used in superconducting magnets, this article deals with the possibilities of increasing the mechanical properties of a superalloy used at cryogenic conditions for structural reinforcement or conduit for supercnducting cables.
Typical structural materials for cryogenic temperatures down to 4.2 K are nickel-bearing austenitic stainless steels, especially the high-nitrogen 316LN austenitic steel. New research and development efforts were oriented towards new grades of superalloys which have not been tested and applied in cryogenic aplications so far. In these applications, excellent combinations of mechanical and physical properties are essential, such as resistance to neutron irradiation and corrosion. The aim of the experimental work was to compare the microstructures and mechanical properties at cryogenic temperatures in an age-hardenable nickel-molybdenum-chromium superalloy after various heat treatment sequences. Several types of precipitates were identified on grain boundaries. Microstructures and mechanical properties of the material were examined and tested. Deformation behaviour was investigated at temperatures ranging from room temperature down to 4.2 K. Scanning electron microscopy and electron backscatter diffraction were used to study the microstructure. The material exhibits high ductility and toughness even at low temperatures.
The fatigue life expectations of some contemporary superconducting magnet designs (ITER Central Solenoid and the NHMFL -Series Connected Hybrid) are considerable, with life cycle requirements for the materials in excess of 1 million cycles at the operating stress ranges. Austenitic steels are the material of choice for many cryogenic structural applications and we have generated a moderate fatigue property database in support of the design and operation of such machines. We have conducted axial tension-tension fatigue tests at liquid helium temperature to generate fatigue life data (S-n curves) on three different austenitic steels (316LN, Nitronic 50, and JK2LB). The fatigue test data presented and analyzed in a form consistent with magnet design code requirements. Metallographic evaluations of the microstructure and fracture surfaces are also presented in support of the test results.
The microstructure of metals and alloys has a significant impact on material properties.
Therefore a detailed investigation of this characteristic is mandatory for the understanding of the behavior of the material of interest.
Beside of the mechanical behavior the impact of the microstructure on thermal and electrical properties is of importance. At cryogenic temperatures thermal processes are hindered and the thermal coupling from inside the material to the cooling fluid depends significantly on the thermal conductivity and heat capacity.
In this work pure copper (OFHC) is used as a reference fcc system with intrinsic stacking fault energy γSFE lower 60 mJm-2 [1], where the grain size can be systematically adjusted by different deformation processes. By severe plastic deformation (SPD), in peculiar the so-called equal channel angular pressing (ECAP) reduce the grain size down to nanometer scale by several consecutive deformation passes.
The distinctive microstructure is characterized by electron backscatter diffraction as well as scanning electron microscopy. Depending on the deformation path, different amounts of twinning, orientation and grain size are observed. Measurements of thermal conductivity and heat capacity are performed. The results are related to the gradually changed grain sizes and examined how far a correlation to mechanical properties is possible.
[1]: J. Freudenberger, A. Kauffmann, H. Klauß, T. Marr, K. Nenkov, V. S. Sarma,, L. Schultz. Studies on recrystallization of single-phase copper alloys by resistance measurements 2010. Acta Materialia , 58, 2324-2329.
Temperature dependence on tensile properties in metallic materials is closely related with the crystal structure: bcc materials exhibit strong dependence and then their strength is increased as lowering temperature while the elongation is dramatically decreased: fcc materials are not sensitive on the temperature and show a good ductility even at cryogenic temperature. The binary system of iron and copper shows a less mutual solubility and Fe-Cu cast forms the ferrite (bcc) and copper (fcc) dual phase structure at room temperature. In this study, tensile properties, deformation and fracture behavior of the rolled Cu-40mass%Fe alloy have been evaluated. The material which showed a good strength and elongation balance at cryogenic temperature formed a layer structure with ultra-fine grains of 1 μm in diameter. In both ferrite and copper grains, furthermore, a lot of precipitates of copper or iron was revealed. Strain was homogeneously distributed at room temperature while it tends rather to concentrate on Cu phase at low temperature. Voids formed in ferrite grains were interrupted to grow around Cu precipitates. Following reasons are considerable: (i) layer structure leads to a good strength elongation balance, (ii) ductility of soft copper grains is enhanced by Fe precipitates at low temperature, and (iii) brittle fracture of ferrite grains is suppressed by dispersed Cu precipitates.
The effect of mean stress or the stress ratio, R, (ratio of minimum stress to maximum stress) on the high-cycle fatigue properties of Ti-5Al-2.5Sn extra-low interstitial (ELI) forging was investigated at 293 K and 77 K. Fatigue tests were carried out for up to ten million cycles at stress ratios of R=-1, 0.01 and 0.5. It is well known that the static strength of metals increases with a decrease in the test temperature and that the fatigue strength tends to depend on the tensile strength at cryogenic temperatures. The high-cycle fatigue strength at each stress ratio of this alloy, however, was relatively lower than that at ambient temperature, although the tensile strength increased with a decrease in temperature. In the failed specimens, facets were observed at the crack initiation site. The crystallographic orientation of the facet was determined by electron backscatter diffraction (EBSD) method in a scanning electron microscope (SEM). In this presentation, the anomalous temperature dependence of high-cycle fatigue strength in this alloy will be discussed based on the results of crystallographic orientation analyses of facets.
Both current and future planned „magnetic fusion reactors" demands very high mechanical properties at cryogenic conditions to ensure superconductivity of magnets and reactor structural integrity at the same time. This paper deals with the possibilities of increasing the mechanical properties of 316LN austenitic stainless steel by means of industrially-feasible thermomechanical processing. Based on available processing maps and numerical simulations a medium-sized upsetting experiment was proposed to enhance the mechanical properties of conventionally processed high-nitrogen 316LN austenitic steel. All processing parameters were chosen with the industrial manufacturability in mind. The experimental sample size was a cylinder with dimensions D40 x 80 mm on which an upsetting of 30% was conducted. Processing temperature T = 1376 K and upsetting velocity ~ 10 mm/s were chosen to achieve fine recrystallized and homogeneous grain. As numerically predicted the experiment geometry ensures a homogeneous deformation in the large volume of the specimen with true strain ~ 0.5 – 0.6. The microstructure was analyzed by means of light microscopy and electron microscopy (SEM + EBSD). Mechanical properties were determined based on tensile tests according to the standards at three different temperatures (300K, 77K, 4K). The reasoning of chosen processing parameters together with the discussion of archived results are presented in the paper.
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Stirling-Type Pulse Tube Cryocooler is widely used in Aerocrafts which are often faced with changing acceleration. While the performance of the cryocooler will decay at the circumstance. Experiments find that both the cryogen’s temperature field in the cold finger and the Compressor’s pistion gap are affected by variable acceleration. A model is made for analyzing the changing of their performance whose result matches the experiment.The experiments is a reference to future cryocooler design.And give a way to control the performance by adding a certain power of compressor.
High frequency pulse tube cryocooler has many advantages，including simple and compact structure, no moving components at cold head, low vibration and low noise. Thus it has become the widespread refrigeration equipment in aerospace field. But the temperature of single-stage pulse tube cryocooler is difficult to reach the temperature range of liquid hydrogen now. In order to reach the temperature range of liquid hydrogen and improve the efficiency of single stage high frequency pulse tube cryocooler, experimental research has been investigated on it in this paper, meanwhile, using the theoretical calculation software Sage to simulate the phase shifter about double-inlet, multi-bypass etc.. The research results will provide a distinct direction for improving the efficiency of the stirling-type pulse tube cryocooler below 20K.
Two-cold-finger pulse tube cryocooler is used to meet the demand of multi-temperature refrigeration. It contains a linear compressor and two cold fingers. A series of cold fingers are tested respectively in this paper first. Then, any two of these cold fingers are chosen to connect the compressor and their performance are tested. Finally, the coupling results are compared. The results show that the size of pulse tube refrigerator, cooling capacity of cold finger and input power of compressor have influence on the gas distribution and phase position. In this study, refrigerating efficiency and coupling efficiency are used to evaluate it’s practicability.
In order to design a high efficient and high-performance pulse tube cryocooler the appropriate size of the cold finger must be found. This study aims to find the relationship between the size and performance of the high frequency miniature pulse tube cryocooler by combining experiment and numerical simulation. The experiments are carried out by changing two aspect: diameter and length of the cold finger. All the experiments are conducted by using coaxial pulse tube. The optimal results of each experiment are compared to find the rule. The experimental results show that the increasing diameter and the decreasing length of pulse tube will improve both the cooling capacity and the optimal frequency.
The inertance of Stirling type pulse tube coolers is an efficient solution for the phase shifter in the 50 – 80 K cooling range. For lower temperature, and especially below 20 K, the phase shifting effect required for the most efficient operation cannot be reached using only inertance. We propose here a new type of phase shifter based on the use of an inertance filled with a high density fluid such as a liquid or high density gas. This design requires the use of a sealed metallic diaphragm to separate the fluid operating in the cold finger from the inertance fluid. The operation has been validated on an 8 K pulse tube cooler. These results demonstrates the capabilities of this setup. Long term operation of the metallic seal membrane has been validated on a dedicated test bench and studies have been made to make the use of this phase shifter possible for space application.
Miniaturization of pulse tube cryocoolers is required for some particular applications, where size and mass for devices are limited, especially in the area of space technology. The high frequency operation leads to reduced pulse tube cryocooler volume for a given cooling power. So the high frequency pulse tube cryocoolers have high energy density and compact structure. Aiming at improving the operating frequency of pulse tube cryocooler, analysis on the difference between 40Hz and 80Hz is worked out. Such as the phasor between mass flow rate and pressure wave, the pressure loss, heat loss etc. Then a shorter regenerator and pulse tube are designed and manufactured. The experimental optimization on the length of regenerators, charging pressure, regenerator matrixes and the combination of inertance tubes are presented. In the end, a cooling power of 10 W at 80 K and a no-load temperature of 40 K are obtained with an input electrical power of 250W, and achieves around 11% of Carnot efficiency at 80K.
A gas-coupled two-stage Stirling-type coaxial pulse tube cryocooler driven by a dual-opposed-piston configuration linear compressor was designed and manufactured with numerical simulation and experiment test based on a high-capacity single-stage pulse tube cryocooler operating at around 40 K. The material and filling method of the regenerator was studied. The mixed stainless steel with different meshes were adopted as the first stage of regenerator, and the Er3Ni was added as the second stage of regenerator. The double-inlet and inertance tube together with room-temperature reservoir were adopted as phase shifter of the first stage, and a new designed double-inlet and cold reservoir were adopted as phase shifter of the second stage. some typical experimental results and considerations for achieving a better performance will also be presented in this paper.
This paper will introduce our recent experimental results of high frequency pulse tube refrigerator. To achieve a temperature below 10 K, two types of two-stage configuration, gas coupled and thermal coupled, have been designed, built and tested. At present, both types can achieve a no-load temperature below 10 K by using only one compressor. The configuration, the phase shifters and the regenerative materials of the developed two types of two-stage high frequency pulse tube refrigerator will be discussed, and some typical experimental results and considerations for achieving a better performance will also be presented in this paper.
Compared with conventional heat pipe, pulsating heat pipe (PHP) takes advantage of several outstanding features, such as great heat transport ability, strong adjustability, small size and simple construction. In our previous work, a 4-turn helium PHP was developed and the effective thermal conductivity was determined to be 4800-13000 W/m∙K, which was dramatically higher than that of copper pipe. However, the temperature difference between the condenser and the evaporator section was too large to cool low temperature superconducting magnets due to the small cross-section area with only 8 channels. In the present work, a helium PHP with small temperature difference for conduction-cooled low temperature superconducting magnets was designed. The effect of several parameters including the number of turns, heat transport distance and liquid filling ratio on the thermal performance of the PHP can be studied by means of experimental and theoretical methods.
This paper explores the development of a 3D model using ANSYS Fluent to characterize the two-phase (gas/liquid) flow of helium in a cryogenic pulsating heat pipe. The model includes condensation and evaporation phenomenon and uses the Vof model to capture aspects of the two phase flow. Temperature dependent properties were applied for helium in the range between 2.2 K and 5.2 K. Bubble formation and movement are observed as well as flow direction at various times in each of the individual pipes. Grid independence tests are performed by plotting the average temperature of different sections. The influence of the number of turns on the performance of php is also investigated.
The High Luminosity LHC (HL-LHC) is a project aiming to upgrade the LHC collider after 2020-2025 in order to increase the integrated luminosity by about one order of magnitude and extend the operation capabilities until 2035. An upgrade of the focusing triplets insertion system for the Atlas and CMS experiments is foreseen using superconducting magnets operating in a pressurised superfluid helium bath at 1.9 K. The increased radiation levels from the particle debris produced by particle collisions in the experiments require that the power converters are placed in radiation shielded zones in an adjacent service gallery, Powering of the magnet over this long distance is achieved by means of an MgB2 superconducting circuit in a 100-m long flexible cryostat transfer line, actively cooled by 4.5 K to 25 K gaseous helium generated close to the magnets. At the highest temperature side the helium flow cools the 20 kA HTS current leads and is recovered at 300 K. At the magnet connection side, a dedicated connection box allows connectivity to the magnets and a controlled boil-off production of helium for cooling needs of the powering system. This paper presents the overall concept of the cryostat system, from the magnet connection boxes, through the flexible cryostat transfer line, to the connection box of the current leads.
Pulsating Heat Pipes (PHP) are passive two-phase heat transfer devices consisting of a long capillary tube bent into many U-turns connecting the cooling part to the heating part. They are thermally driven by an oscillatory flow of liquid slugs and vapor plugs coming from phase changes and pressure differences along the tube. The coupling of hydrodynamic and thermodynamic effects allows high heat transfer performances.
Three closed-loop pulsating heat pipes have been developed by the SACM (Accelerators, Cryogenics and Magnetism Department) of Saclay, France. Each PHP measures 3.7 meters long (0.33 m the cooling and heating parts and 3 m the adiabatic part), representing almost 20 times longer than the longest existing cryogenic PHP. These PHPs have 36, 22 and 12 parallel channels. One hundred tests have been performed in horizontal position (the most similar configuration to no-gravity characteristics) using nitrogen as working fluid, operating between 75 K and 90 K. The inner and outer diameters of the stainless steel capillary tubes are 1.5 and 2 mm respectively. The PHPs were operated at different filling ratios (20% to 90%), heat input powers (3W to 20 W) and evaporator and condenser temperatures (75 K to 90 K).
As a result, the PHP with 36 parallel channels achieves a certain level of stability during more than thirty minutes with an effective thermal conductivity up to 200 kW/m·K at 10 W heat load and during forty minutes with an effective thermal conductivity of 300 kW/m·K at 5 W heat load.
In this paper, a detailed experimental study was carried out to investigate the two phase flow patterns of R600a in a smooth horizontal tube with an inner diameter of 6 mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415 MPa, mass fluxes from 67 to 194 kg m-2 s-1 and heat fluxes from 10.6 to 75.0 kW m-2. Based on high speed camera four main flow regimes can be identified: Plug flow, Stratified-wavy flow, Slug flow and Annular flow. Intermittent flow(include plug and slug flow) to Annular flow transition was detected and plotted on flow pattern map. Comparisons with available intermittent/annular (I/A) transition lines in the literature have been made. Finally, a transition equation of intermittent/annular flow for R600a was proposed by introducing four dimensionless parameters.
The experiment PVLAS1) aims at the measurement of the vacuum polarization as predicted by the QED (Quantum Electro Dynamics).In the new experimental set-up2) at INFN Ferrara two mirrors, 3.5 meter apart, constitute an optical cavity (with finesse=700 000) for a 1.064 micron Laser. Between the two mirrors two independent high field permanent dipole magnets (Halbach type) are installed, which can rotate up to 10 Hz around their longitudinal axis.
In order to reduce the thermal noise of the mirrors their temperature will be lowered trough a “cold finger” immersed in liquid Nitrogen (LN2). The mirrors must have the possibility to rotate of 360 degrees and to be tilted of about one degree. As a consequence the mirrors are cooled by radiation without any physical contact to the cold finger. A test set-up has been constructed at the INFN Laboratori Nazionali di Legnaro in order to measure the ultimate temperature that the mirrors can achieve. Details will be given in the report.
1)R.Pengo et al., An original rotating cryostat for the experiment PVLAS, in Proceedings of ICEC 17, Bournemouth,UK, July 1998, p.851,
2) F. Della Valle et al., The PVLAS experiment: measuring vacuum magnetic birefringence and dichroism with a birefringent Fabry-Perot cavity, Eur. Phys. J. C (2016) 76:24
In this paper, oscillating flow in heater and cooler of β-type Free-Piston Stirling Engine (FPSE) have been investigated in order to highlight the impact of alternating heat transfer on its performance. This analysis is based on the Finite Speed Thermodynamics and Isothermal methods, considering different heat and power losses in Stirling Engine, meanwhile physical modeling are carried out by GAMBIT software and numerical solution about models of the heater and the cooler are also obtained through commercial software FLUENT. Simulation results are compared with experimental results obtained from self-development 100W β-type FPSE. According to the results, the heat transfer correlations of oscillating flow in heater and cooler have been provided and discussed. By optimizing structural in heater and cooler, the performance of Stirling Engine is over 25% in our laboratory.
The detectors of the Super Cryogenic Dark Matter Search (SuperCDMS) experiment at SNOLAB will operate in a six-layered cryostat with thermal stages between room temperature and the base temperature of 15 mK. The inner three layers of the cryostat, which are to be nominally maintained at 1 K, 250 mK, and 15 mK, will be cooled by a dilution refrigerator via conduction through long copper stems. Bolted and mechanically pressed contacts, both flat and cylindrical, as well as flexible straps are the essential stem components that will facilitate assembly and will allow for thermal contractions/movements during cooldown of the sub-Kelvin circuit. To ensure that these components and their contacts meet their design thermal conductance, they are being fabricated and cryogenically tested at the Fermilab milli-Kelvin facility. This paper will overview the SuperCDMS-SNOLAB sub-Kelvin architecture, summarize the conductance requirements, and present results of the thermal conductance measurements.
Cryosorption pump is a capture vacuum pump which retains gas molecules by chemical or physical interaction on their internal surfaces when cooled to cryogenic temperatures. Cryosorption pumps are only the solution in nuclear fusion systems to achieve high vacuum in the environment of hydrogen and helium. An important aspect of this development is the proper adhesion of the activated carbons on the metallic panels using a high thermal conductivity and high bonding strength adhesive. Typical adhesives used are epoxy based. The thermal conductivity of the adhesive can be improved by using fine aluminium powder as the filler in the base epoxy matrix. However, the thermal conductivity data of such epoxy-aluminium composites is not available in literature. Hence, we have measured the thermal conductivities of the above epoxy-aluminium composites (with varied volume fraction of aluminium in epoxy) in the temperature range from 4.5 K to 300 K using a GM cryocooler based thermal conductivity based experimental set-up. The above results are discussed in this work. These studies will be useful towards the development of cryosoprtiom pumps with high pumping speeds.
The hybrid magnet which consists of a 34T resistive inserts and an 11T superconducting outsert has been put into operation early this year at CHMFL. The superconducting outsert made of Nb3Sn CICC is cooled with forced flow supercritical helium at 4.5 K. The main helium cryogenic system includes a helium refrigerator and a helium distribution system for the cooling of superconducting coils, structures, transfer lines and current leads. The helium refrigerator was successfully commissioned at early 2012 and has been operated at liquefaction mode for 5 years. The helium distribution system assembly was finished, and then the first commissioning of helium cryogenic system was carried out at the end of 2016. In this paper, assembly and commissioning of the helium cryogenic system for the hybrid superconducting outsert will be presented.
China Spallation Neutron Source(CSNS) cryogenic system provides supercritical cryogenic hydrogen to neutron moderator, including a helium refrigerator, hydrogen loop and the hydrogen safety system. The helium refrigerator is provided by linde with cooling capacity of 2200W at 20 K. Hydrogen loop mainly includes hydrogen circulator, ortho-para convertor, helium-hydrogen heatexchanger, hydrogen heater and accumulator. These equipments are integrated in hydrogen circulation cold box and accumulator cold box. Hydrogen safety system includes safety valve, rupture disk, hydrogen sensor, and other equipments to ensure that cryogenic system in dangerous situations will goes down, vents or takes other measures. At present, all the equipments have been installed, and neutron moderator will be connected in the near future. To verify the cryogenic system accords with the design requirements, we use the heater instead of neutron moderator for commissioning. First, in the case of using helium, cryogenic system cooled to 20K, then stop and leak detection. Second, in the case of using hydrogen cooled down to 20K, optimizing the control logic. After the completion of the cryogenic system commissioning, the next step is cryogenic system connecting with moderator for commissioning, in the case of helium and hydrogen, and the last step is CSNS joint commissioning.
SBN Near Detector cryogenic system, planned to be commenced into operations at Fermilab in 2019, is being designed to match number of scientific and technical requirements. The poster provides background material to facilitate discussions of proposed operation modes and selection of equipment with specific emphasis of implementation “lessons learned” from operations of Fermilab LAPD, 35T and MicroBooNE cryogenic systems.
Toroidal field magnets of ITER cryogenic system contain over 7 ton of helium. Most of the inventory is expelled from the magnets n case of a quench and it needs to be captured in an external storage vessels (Quench Tanks). Force cooled technology with external gas circulation was chosen for these vessels in order to optimize their footprint and costs.
This paper outlines the input data, assumptions and studies performed in order to choose the most appropriate technology for the Quench Tanks. Further studies to demonstrate feasibility and ensure the required performance, as well as some peculiarities of the manufacturing and handling Quench Tanks are also described.
The future electron ion collider at Brookhaven National Lab consists of using one existing hadron ring and developing a new electron accelerator. This paper presents the cryogenic loads for the hadron ring’s superconducting ring and related upgrades to handle the additional loads. The cryogenic loads for the superconducting RF injector/accelerator and storage ring for the electron beam are summarized. The proposed cryogenic plants and system configurations options are presented.
The Circular Electron Positron Collider（CEPC）is a superconducting collider and it is currently under the conceptual design. CEPC will adopt 256 1.3 GHz 9-cell superconducting cavities in the booster ring and 384 650 MHz 2-cell cavities in the collider ring for the 120GeV beam energy. The superconducting cavities will operate at 2 K temperature. A large cryogenic system with the cooling capacity of about 100KW equivalent at 4.5K will be required in CEPC project. The cryogenic system consists mainly of two helium refrigeration plants and their distribution system. This presentation introduces the status on conceptual design of CEPC cryogenic system including the heat loads estimated and preliminary layout and flow scheme and so on.
Originally the spoke test cavity cryostat was designed to test exclusively SSR1 cavities. The goal of this upgrade is to extend this capability to SSR2 cavities, and to low and high beta 650 MHz cavities. These cavities are the last elements of the superconducting linac architecture which is the main component of the Proton Improvement Plan-II (PIP-II) at Fermilab.
The size of SSR2 and 650 MHz cavities being much bigger than SSR1, extensions of the vacuum vessel and of all the cryogenic lines have been necessary. Mechanical, thermal and cryogenic analyses have been performed to ensure proper operation. This paper summarizes the design choices which have been made by describing the main elements of this upgrade and the interface between cryogenic lines and cavities.
Big scientific facilities which use cryogenic technologies usually need to transfer cooling power from one or several cryogenic plants to cryogenic users. Typical cryogenic users are cryomodules with superconducting radiofrequency cavities and cryostats with superconducting magnets that are immersed in liquid helium. Due to the complex architecture of the cryogenic systems, the cold helium usually needs to be not only transferred in long distances, but also precisely distributed among the different users. This requires cryogenic distribution systems which include a number of valve boxes at the interfaces to the cryomodules and magnet cryostats. A good example of such systems is the LHC cryogenic distribution, which is composed of eight 3.3 km long cryolines, each including 25 or so valve boxes. Another example is the ESS linac cryogenic distribution system, currently under construction at European Spallation Source ERIC in Lund, Sweden. This system is only 370 m in length but it comprises 43 valve boxes and one return box.
Such systems include a tremendous number of components (valves, temperature and pressure sensors, bellows, flexible hoses etc.) which can malfunction or get damaged in many ways leading to unwanted shut downs of the entire facility. In order to avoid these problems or mitigate their consequences the systems should be properly operated and maintained. This requires planning of maintenance works, storing spare parts and ordering some service works.
The paper presents a maintenance strategy for a multi-valve cryogenic distribution system. Possible failures of the system components are identified and all the required maintenance and reparation works are described. The presented maintenance algorithm is intended to support decision-making on spare part and service cost minimizations.
Note: The authors do not have any conflict of interest and have not received any payment for co-authoring this paper.
The multi-process pipe vacuum jacketed cryolines for the ITER project are probably world’s most complex cryolines in terms of layout, load cases, quality, safety and regulatory requirements. The risk mitigation plan of Indian Domestic Agency (IN DA), who is responsible for the supply and installation of ITER cryolines, included design, manufacturing and testing of prototype cryoline (PTCL) before the approval of final design of ITER cryolines.
The 28 meter long PTCL consist of 6 process pipes encased by thermal shield inside outer vacuum jacket (OVJ) of DN 600 size and carries cold helium at 4.5K and 80K. The global heat load limit was defined as 1.2 W/m at 4.5K and 4.5 W/m at 80K. The PTCL-X (PTCL for Group-X cryolines) was specified in detail by ITER-India and designed as well as manufactured by Air Liquide. PTCL-X was installed at ITER-India Cryogenic Laboratory in during July-August-2016, pressure and leak tests at room temperature were performed in September-2016 followed by cold test in October-2016. The temperatures, pressures and mass flow of helium flowing through PTCL-X were measured during the cold test. The heat load at 4.5K and 80K, estimated using enthalpy difference method, was found to be approximately 0.8 W/m at 4.5K, 4.2 W/m at 80K, which is well within the defined limits. Thermal shield temperature profile was also found to be satisfactory. Paper summarizes the cold test results of PTCL-X.
Johnston couplings are used for detachable connections of flexible cryogenic transfer lines to stationary plant components. There are different solutions for this purpose, the technical design of which differs mainly according to the utilized fluid properties and the connection dimensions. Within the framework of a project for the MITICA facility, meant to test in advance the ITER Neutral Beam injectors and its cryo-pumping system, a compact cryogenic coupling for 4K Supercritical and 80K gaseous He, which is suitable for operation in any mounting orientation, with stringent heat load requirements in a challenging ionizing radiation environment, has been developed. The coupling can be manually coupled, but is also designed for implementing a remote operation system in the future.
This paper describes the design aspects and explains how the design requirements have been confirmed by simulations and functional test, performed on a full scale prototype.
A hybrid magnet which is capable of producing more than 40 T steady field has been put into operation eraly this year at CHMFL. The superconducting outsert of the hybrid magnet is wound with Nb3Sn CICC and cooled with forced flow supercritical helium at 4.5 K. A multi-channel cryogenic transfer line is mounted between the magnet cryostat and the cryo-distribution box to transfer supercritical helium and electric current. Inside the cryogenic transfer line there are four pipes for helium feeding, two pipes for helium return, a pair of busbars and several electrical joints. Also a vacuum barrier is located at the intermediate section in order to ensure the independence of the vacuum of the magnet cryostat and the cryo-distribution box. Design, assembly and testing of the cryogenic transfer line will be presented in this paper.
Meyer Tool & Mfg., Inc (Meyer Tool) of Oak Lawn, Illinois is manufacturing a cryogenic distribution box for Fermi National Accelerator Laboratory (FNAL). The distribution box will be used for the Muon-to-electron conversion (Mu2e) experiment. The box includes twenty-seven cryogenic valves, two heat exchangers, a thermal shield, and an internal nitrogen separator vessel, all contained within a six foot diameter ASME coded vacuum vessel. This paper discusses the design and manufacturing processes that were implemented to meet the unique fabrication requirements of this distribution box. Design and manufacturing features discussed include: 1) Thermal strap design and fabrication, 2) Evolution of piping connections to heat exchangers, 3) Nitrogen phase separator design, 4) ASME code design of vacuum vessel, and 5) Cryogenic valve installation.
The heat leakage of cryogenic transfer lines directly influences the performance of the large-scale helium refrigerator. In this paper, the thermal mode of cryogenic transfer line considering temperature distribution and heat leakage of support and multilayer insulation was established. To validate the model, the test system of cryogenic transfer lines with good thermal shield and changing easily heat insulating material has been built. The experimental result of the heat leakage through the overall length, support and the multilayer insulation were obtained and the overall leakage is 1.58W/m. The differences of heat leakage and temperature distribution between experimental and simulated results were less than 7%, which verifies the theoretical model in this paper. In order to reduce the overall heat leakage of cryogenic transfer lines further, the optimized structure of support will be designed based on the above analysis of the thermal model and test system in the near future.
Key word: cryogenic transfer line; heat leakage; multilayer insulation; support; large-scale helium refrigerator
Acknowledgement
This work was supported by the fund of National Research and Development Project for Key Scientific Instruments. (ZDYZ2014-1)
Since the conceptual design review of the ITER Cryodistribution (CD) many modifications and changes have been applied due to both system optimization and improved knowledge of the clients’ requirements. The CD, consisting of one Cryoplant Termination Cold Box (CTCB), five Auxiliary Cold Boxes (ACBs) and one Thermal Shield Cold Valve Box (TCVB), distributes the cooling power generated in the Cryoplant to the clients at proper conditions to sustain the Tokamak plasma experiments. Process optimizations of the Cryoplant resulted in simplifications of the CTCB internal configuration which is collecting the cooling power of the Cryoplant and transferring it to the ACBs and TCVB. Increased heat load in some of the superconducting magnet systems required the ACBs, where the conditions for forced convection cooling are prepared, to be modified for more flexible and economical operation from a cooling power point of view. Due to the removal of the redundant helium manifolds in the Tokamak thermal shields, one of the two TCVBs could be removed. In this proceeding we will introduce the present design status and component configuration of the ITER CD with all the changes implemented which aim at process optimization and simplification as well as operational reliability, stability and flexibility.
The helium recovery and purification system at the IHEP is build to recover and repurify helium containing 10% water saturated air at a rate of 210 Nm3/h and a pressure of 1.05 bar to a contaminant level below 5ppm. Low pressure gas is recovered through a pipeline from the BEPCII cryogenic system， ADS-inject I cryogenic system，and other cryogenic equipment test which evaporate the impurity helium gas.
The impurity helium gas, which is compressed from 1.05bar to 200bar with the flow rate of 210m3/h, are compressed into impurity gas cylinder. The impure helium gas is purified to the purify helium, which are stored in the purified helium gas cylinder, by the LN2 cooled adsorber. Total LN2 consumption is 200L/h. When any buffer tank need the helium gas, the system can distribute the purified gas helium from the purified gas cylinder to the A，B，or 1# tank.
Superconducting motors and generators offer numerous advantages over conventional generators of the same rating. They are lighter, smaller and more efficient. Amongst a host of methods for cooling HTS machinery, thermosyphon-based cooling systems have been employed due to their high heat transfer rate and near-isothermal operating characteristics associated with them. So it is essential to study thermal characteristics of these cryogenic thermosyphons. To this end, a stand-alone neon thermosyphon cooling system resembling an HTS rotating machine was studied. Heat load tests were conducted on the neon thermosyphon cooling system by applying a series of heat loads to the evaporator at different filling ratios. The temperature at selected points of evaporator, adiabatic tube and condenser as well as total heat invation were measured. A further study involving a computer thermal model was conducted to estimate temperature distribution of thermosyphon components and heat invation of the cooling system. The model used boundary conditions corresponding to data of heat load tests. This work presents a comparison between estimated and experimental temperature distribution of the two-phase cryogenic thermosyphon cooling system. The simulation results of temperature distribution and heat invasion compared generally well with experimental data.
Superconducting power systems with multiple superconducting devices are being designed for all electric ships and aircrafts. Efficient and flexible power systems with multiple superconducting devices will be possible with a large capacity centralized cryogenic plant serving all the devices. The centralized cryogenic system will have higher efficiency and requires fewer spare components compared to the distributed/dedicated cryogenic systems. The centralized approach will also allow the cryogenic plan at a location most convenient for system architecture in terms of cooling water supply, space restrictions, and noise issues. The superconducting power system with centralized cryogenic system needs to be studied for transient behavior in various operating scenarios to evaluate the temperature gradients across individual devices and the effect of an unexpected heat load from one of the devices. For superconducting power systems, the heat loads originate from outside the system through heat leaks and within the system through joule heating. Hence coupled thermal and electrical models are necessary to describe the systems. Thermal network models have been used to couple the electrical and thermal aspects of superconducting systems. This paper expands the thermal network models for studying systems with multiple superconducting devices with a common cryogenic fluid circulation loop. The response of the system is evaluated for various operating conditions including typical failure modes of cryogenic systems, such as breakdown of circulation pumps or cryocoolers and vacuum insulation breach. The paper presents the modelling methodology, challenges encountered, solutions devised, and the results of several cases with various operating scenarios.
The work is funded by the Office of Naval Research.
High Temperature Superconducting (HTS) synchronous motors consisting of HTS windings in the rotor and air gap copper windings in the stator will help in manufacturing compact, lighter motors with a high torque to weight ratio, low noise and better dynamic response needed for strategic applications. The development of HTS field coil is one of the main technological challenges in the development of a HTS motor as it involves the selection of HTS wire, winding technology, handling of the HTS wire while winding on a winding machine and testing of the developed coil at cryogenic temperatures. In the present work, a HTS field coil with double pancake coils in the shape of a racetrack wound using HTS tape was fabricated. An indigenously developed winding machine available at BHEL R & D is used for winding of double pancake coils. The design details, development details and testing results of the HTS field coil are presented in this paper.
The sophisticated cooling system is required for High temperature superconductor (HTS) applications. Especially, HTS rotating machine have to keep the temperature of field poles under 40 K with rotating.
A thermosyphon (TS) cooling system has been employed for HTS rotating machine. TS cooling is based on natural convection of coolant, it doesn’t need mechanical circulator. The feature of a TS cooling system is simple and light weight mechanical composition and the high heat transfer coefficient by utilizing latent heat.
The operating temperature of a TS cooling system is depends on the saturation temperature of coolant. This means an internal pressure affects the performance of a TS cooling system.
In this paper, we focused to the internal pressure for a TS cooling system using a 100 W-grade TS cooling system with rotating part. We carried out the heat load test with variety condenser temperatures with rotating. The internal pressure increase due to the heat load increment and/or condenser temperature increment. Moreover, the rotating is n’t affected for internal pressure. This result shows the internal pressure is in proportion to the difference temperature between condenser temperatures to saturation temperature calculated by internal pressure.
These results provide the cryogenic design with a HTS rotating machine cooled by TS.
Supercritical helium is often used to reduce the temperature fluctuation caused by the second stage of the G-M cryocooler, however the natural convection of the supercritical helium has a great influence on the suppression of the temperature oscillation.To do experimental research on the effect of natural convection on temperature fluctuation suppression, three different forms of helium pots are designed and fabricated: (1) the barrel of the container is stainless, no copper bar in the container(1# helium pot); (2) the barrel of the helium pot is pure copper, no copper bar in the container(2# helium pot); (3) the barrel of the helium pot is stainless, nineteen copper bar in the container(3# helium pot). By measuring the temperature of the cold head and the bottom of the helium pot change with time, we studied the impact of the helium pressure, the structure of the helium pot, and the heat flux on the temperature fluctuation suppression with the method of fast Fourier transform.
Liquid hydrogen has excellent physical properties, high latent heat and low viscosity of liquid, as a coolant for high critical temperature superconductors like MgB2. The knowledge of DNB (Departure from Nucleate Boiling) heat flux of liquid hydrogen is necessary for design and cooling analysis of high critical temperature superconducting devices.
In this paper, DNB heat fluxes of liquid hydrogen were measured under saturated and subcooled conditions at the pressure of 0.4, 0.7 and 1.1 MPa for various flow velocity in the range of 0.5 m/s to 15 m/s. Two round test heaters made by Pt-Co alloy with the length of 200 mm and the diameter of 0.7 mm were used. These heaters were assumed superconducting wire. And these round heaters were set in central axis of a flow channel made of GFRP with the inner diameter of 8 and 12 mm respectively. These test bodys were vertically mounted and liquid hydrogen flowed upward through the channel.
The experimental values show DNB heat fluxes for flow velocity curve consists of a slower flow velocity region with a higher gradient and faster flow velocity region with a lower gradient. Considering the use of liquid-hydrogen for superconductors cooling, it can be said the efficient flow velocity for cooling exists in industrial use.
From these experimental values, the correlations of DNB heat flux under saturated and subcooled conditions for the vertically mounted heater set in central axis are presented in this paper. This correlations represent the value of DNB heat fluxes within 15 % error compared with the experimental values.
This research was supported in part by JST, ALCA. The author thanks the technical staffs of JAXA for their support in this experiment.
Long-term preservation of cells and tissues require adequate freezing protocols in order to increase viability after storage in liquid nitrogen temperatures. Way of cooling down the biological material to cryogenic temperatures is noticed as a most dangerous stage in preservation. Possible cryo-injuries caused by direct action of ice or volumetric increase inside the single cell are formed mainly during this time. Delicate structure of cell could be affected by several damages concerning to intra- and extracellular ice formation. To avoid this problem novel solutions have been presented in nowadays research included development in the cryo-containers and different cooling techniques. One of the most popular technique presented is vitrification – amorphous solidification of a supercooled liquid without any internal crystallization. To reach the ice-free state of cell suspension is requiring to add cryoprotectants into solution and reach high enough cooling rates during freezing process. Ordinary cryopreservation protocols for vitrification are designed based on inefficient liquid nitrogen plunging methods. The paper presents novel method for cryopreservation by usage of micro-solid nitrogen particulate spray cooling. Particulate spray is considered as potential solution to reach high enough cooling rates thanks to avoid film boiling formation, and to enhance heat transfer coefficient due to forced convection of the coolant. Especially for water solution with cryoprotectant, the experimental set-up was constructed in order to check the thermal performances and vitrification achievements. Presented investigation shows capabilities of high heat flux spray cooling. To clarify increase performance of micro-solid nitrogen spray, obtained data were compared with standard cryopreservation techniques reported in literature.
Chill down of cryogenic transfer lines is a crucial part of cryogenic propulsion as chill down ensures transfer of single phase fluid to the storage tanks of cryogenic engine as well as also ensures single phase liquid flow during start of the engine. Chill down time depends on several parameters such as length of the pipe, pipe size, orientation, mass flux etc. For all these experiments, outer surface temperature is measured at different axial locations as well as in azimuthal planes. Studies are carried out at different inlet pressures and mass flux to understand the effect of these parameters. Two different pipe sizes are taken to study the effect of variation in diameter, stratification, chill down time and quantity of cryogen required. Different orientations are taken to understand its effect on the chill down time, heat transfer coefficient and critical heat flux for the same inlet pressure and mass flux. Pressure drop is also measured for all these cases and compared with the calculated value for each case. Pipe inner wall temperature, heat transfer coefficient for different pool boiling regimes and critical heat flux are calculated based on measured outer surface temperature history for each case. These results also give an insight for variation of heat transfer coefficient in different flow regimes for same mass flux and inlet pressure for different orientations.
A one dimensional energy conservation equation is solved for transient chill down process considering the constant mass flux and inlet pressure to predict the chill-down time. Temperature variation during chill down obtained from the numerical simulations are compared with the measured temperature history.
Keywords: Cryogenics, Chill down, Heat transfer Coefficient, Critical Heat Flux
The knowledge of forced flow heat transfer characteristics of liquid hydrogen (LH2) is important and necessary for design and cooling analysis of high critical temperature superconducting devices. However, there is few test facility of LH2 forced flow cooling for superconductors. We have already developed such a test system that it can make a LH2 forced flow (~10 m/s) of short period (less than 100 s). The test system was composed of two LH2 tanks connected by a transfer line with a controllable valve, where the forced flow rate and its period were limited by the storage capacity of tanks. In this paper, we describe a liquid hydrogen recirculation system which was designed and fabricated in order to study characteristics of superconducting cables in a stable forced flow of liquid hydrogen for a long period. This LH2 loop system consists of a centrifugal pump with dynamic gas bearings, a heat exchanger which is immersed in a liquid hydrogen tank, and a buffer tank where a test section (superconducting wires or cables) is set. The buffer tank has LHe cooled superconducting magnet which can produce an external magnetic field (up to 7T) at the test section. A performance test was conducted. The maximum flow rate was 43.7 g/s. The lowest temperature was 22.5 K. It was confirmed that the liquid hydrogen can stably circulate for 7 hours.
In refrigeration applications, hydrocarbons have high thermodynamic performances and belong to the group of natural refrigerants. Especially in mixture Joule-Thomson low temperature refrigerators (MJTR), hydrocarbons (methane, ethane, propane and butane) are the main components and have acquired wide applications.
A brief literature survey is made on the flow condensation study of hydrocarbons. The principal experimental work in the literature is described. Then, a description of widely quoted flow condensation heat transfer prediction methods is presented. Since there are few specific prediction methods for hydrocarbon, five flow condensation heat transfer prediction model were selected to compare to the experimental data from the available studies. The comparisons only focus on flow condensation in plain tubes.
Based on the basis of the comparisons and analysis, a new flow condensation heat transfer model based on the flow condensation heat transfer mechanisms for horizontal tubes have been developed specifically for hydrocarbons. Firstly, a new evaluation of condensation contribution in flow condensation heat transfer has been proposed for hydrocarbons. Secondly, a new correlation for the factor describing the contribution of condensation has been proposed based on the condensation heat transfer mechanisms. It incorporated the influence of liquid film thickness and vapor quality. Thirdly, a forced convection heat transfer enhancement factor correlation incorporating liquid velocity has been proposed based on the convective heat transfer mechanisms so as to capture the trends in the flow condensation heat transfer data. In addition, the comparisons of the new model and other classic models, as well as the comparison of experimental values and predicted values for low-boiling hydrocarbons, were made to evaluate the accuracy of the new heat transfer model.
As one kind of natural refrigerants, R170 and its mixtures can be used to replace R22 and R503 in some refrigerators and heat pump systems. For example, R170 is an important component of mixed-refrigerants for the low-temperature Joule-Thomson refrigerator. With various mixed-components, the system can achieve different performances. Accurate knowledge of the heat transfer of pure fluids is the first process in understanding the behavior of the multi-component mixtures. Thus, in order to appropriate use R170 and its mixtures, the condensation heat transfer data of R170 are very important.
In this work, condensation heat transfer of R170 in a horizontal smooth tube with inner diameter of 4 mm is numerically simulated with VOF model. The vapor and liquid phases are assumed to be turbulent and laminar, respectively. The inlet saturation pressure of R170 is 2 MPa and the average wall heat flux is 60 kW m-2, mass fluxes vary from 100 kg m-2 s−1 to 250 kg m-2 s−1. The simulation results show that the heat transfer coefficient increases with the increasing vapor qualities and the increasing mass fluxes. These numerical heat transfer data agreed well with the previous experimental results. In addition, in this paper, the variation of heat transfer coefficient and liquid film thickness along the tube is also simulated, respectively. Along the flow direction, the heat transfer coefficient becomes smaller, the liquid film thickness at the bottom of the tube increases consistently which means gravity effect shouldn't be neglected in the present work. Furthermore, transition flow, slug flow and plug flow had been numerically observed in this simulation, these flow patterns similar with the previous experimental phenomena.
Achieving high current superconducting wires for large scale applications and magnets has been one of the most challenging objectives during all the HTS era. Coated conductors of YBa2Cu3O7 (YBCO) have emerged as the most attractive opportunity to achieve unique performances while reducing the cost/performance ratio continues to be a key objective at present. Chemical solution deposition (CSD) is a very competitive cost-effective technique which has been used to obtain nanocomposite films and CCs. In the recent years we have been able to demonstrate the unique potentiality of these CSD techniques to achieve low cost, low anisotropy and high critical current coated conductors. In my presentation, I will report on the present understanding of vortex pinning in CSD nanocomposite YBCO films at different temperatures and magnetic fields, obtained from complex solutions where the nanoparticles are spontaneously segregated during growth and the novel strategy using colloidal solutions of preformed oxide nanoparticles (NPs) stabilized in the YBCO precursor solutions. A thorough investigation correlating the pinning landscape with the defect microstructure has been pursuit with detailed angular dependent in-field critical currents and HRTEM/STEM analysis. I will also report on a new approach we are investigating based on low cost nanocomposite CSD crystallization through a transient-liquid assisted growth (TLAG) enabling ultrafast growth rates in the range of 50 nm/s.
This research has been funded by EU-ERC_AdG-2014-669504ULTRASUPERTAPE project, EU-FP7 NMP-LA-2012-280432 EUROTAPES project and Excellence Program Severo Ochoa SEV2015-0496
The Fe-based superconductors (FBS) present a large variety of compounds whose properties, including flux pinning, are affected to different extents by their crystal structures. The doped $AEFe_2As_2$ phases ($AE = Ba,Sr$) mostly show a 3D character similar to low-$T_c$ superconductors and can accept a high density of artificial pinning centers. On the contrary, the $REFeAs(O,F)$ family ($RE1111$, $RE$ rare earth element) has the highest critical temperature $T_c$ (~58 K in bulk form) among FBS and a large upper critical field anisotropy that induce properties more similar to high-$T_c$ superconductors (HTS). Here we investigated the pinning properties of Nd1111 in flux-creep regime.[1] For $H//c$ the critical current density $J_c$ can be described by standard mechanisms such as point/planar defect pinning and vortex shearing. When the field approaches the $ab$-planes two different regimes are observed at low temperatures as a consequence of the transition between 3D-Abrikosov and 2D-Josephson vortices: one is determined by the formation of a vortex staircase structure, which suppresses the $n$-value ($V \sim I^n$ ), the other one by the lock-in of the vortices parallel to the layers, which induces an increase of $n$. This is the first study on FBS showing this behavior in a full temperature, field, and angular range and demonstrates that, despite the relatively low $T_c$ and anisotropy of Nd1111 compared to HTS, this compound is substantially affected by intrinsic pinning similarly to $YBa_2Cu_3O_{7-\delta}$.
A portion of this work was performed at the National High Magnetic Field Laboratory, supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and State of Florida. The research leading to these results has received funding from European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement 283141 (IRON-SEA) and supported by Strategic International Collaborative Research Program (SICORP), Japan Science and Technology Agency.
[1] Tarantini et al. Scientific Reports 6, 36047 (2016).
Iron-based superconductors have attracted a great deal of interests in both fundamental physics and potential applications. We have grown iron-chalcogenide FeSe0.5Te0.5 (FST) superconducting films on various single crystal substrates and metal substrates in coated conductors by pulsed laser deposition.[1] The FST films on CeO2 buffer layer exhibit enhanced transition temperature Tc (onset Tc = 20 K, zero resistance Tc = 18 K), which is about 30% higher than that found in the bulk materials, and carry high critical current density Jc more than 1 MA/cm2 in self-field and 0.1 MA/cm2 under 35 T at 4.2 K.[2] In this talk, we present a route for simultaneous increase of Tc and Jc in FST films by low-energy proton irradiation.[3]
A robust enhancement of Tc and Jc has been realized simultaneously in the FST film irradiated with 190 keV proton, resulting in an increase of zero resistance Tc from 18.0 K to 18.5 K and an increase of Jc at 12 K by one order of magnitude after the irradiation at applied magnetic field over 15 T for H//ab and over 6 T for H//c. Extensive transmission electron microscopy analysis provides direct atomic-scale imaging of cascade defects and the surrounding nanoscale strain field produced by low-energy proton irradiation. Our studies opened up the possibility to achieve significant enhancement of Jc without Tc reduction through the design of vortex pinning landscape by low-energy ion irradiation for superconducting films.
1) Q. Li et al., Rep. Prog. Phys. 74, 124510 (2011).
2) W. Si et al., Nat. Commun. 4, 1347 (2013).
3) T. Ozaki et al., Nat. Commun. 7, 13036 (2016).
Interfilamentary bridging in Bi2212 conductors influences the magnetization of magnets built using these conductors. Previous work has shown that the magnetization depends linearly on sample length and twist pitch, and a length-independent parameter describing the connectivity between superconducting filaments was introduced. However, this parameter has not yet been correlated to the bridged microstructure of Bi2212 wires. In this work, we use quantitative SEM studies made on cross sectional and longitudinal sample mounts of 85 x 18 filament Bi2212 wires to correlate the connectivity parameters, calculated for helical Bi2212 samples of various lengths (L) and twist pitches (Lp) and generated by inputting M-H and transport measurement results into a mathematical model, with their microstructures. In addition to generating homogeneous high magnetic fields, magnets used in accelerators should generate time-invariant magnetic fields. Flux creep has been shown to be significant in high temperature superconductors even at low temperatures, and thus it may cause the magnetic field of the magnet to drift with time. In this work, we show that not only the magnetization, but also the magnetic relaxation rates of Bi2212 strands are L and Lp dependence. Magnetization decay over 1200 s was measured as a function of L and Lp in transverse applied magnetic fields of 0-12 T. Magnetization decay was observed to increase by about 40% for samples with the largest L or Lp as compared to the samples with the smallest L and Lp. These results are interpreted in terms of weak bridging current induced anisotropy.
In this work, segment of various HTS cables were measured for loss at high dB/dt in a rotating magnet AC loss machine. The cables types including CORC, Roebel, and TWST cables, and for the CORC cables, striations were present for some samples. The cable were measured in a recently described spinning magnet calorimeter (SMC). This test device has a spinning rotor which consists of permanent magnets arranged in a Halbach array, with the sample exposed to an AC field of 0.566 T (peak) and a radial dB/dt of 272 T/s (tangential, Bmax = 0.242 T, dB/dt = 125 T/s). Loss is measured using nitrogen boiloff from a double wall calorimeter feeding a gas flow meter. For comparison, a straight segment of tape of the kind used in the cable was also measured in a field perpendicular to the wide face of the tape. The results were compared to a simple analytic models for losses of these conductors and the starting tape. The losses of the cables were compared, as well as the amount of strand coupling vs hysteretic loss present in each. The coupling loss was moderate for the TWST, and small for the Roebel and CORC, but the loss was dominated by hysteretic losses in all cases. The influence of applied field amplitude and demagnetization on field penetration was discussed.
The solder joints in spaceflight high temperature superconductor (HTS) lead assemblies for certain astrophysics missions have strict constraints on size and power dissipation. In addition, the joints must tolerate years of storage at room temperature, many thermal cycles, and several vibration tests between their manufacture and their final operation on orbit. As reported previously, solder joints between REBCO coated conductors and normal metal traces for the Astro-H mission showed low temperature joint resistance that grew approximately as log time over the course of months. Although the assemblies worked without issue in orbit, for the upcoming X-ray Astrophysics Recovery Mission we are attempting to improve our solder process to give lower, more stable, and more consistent joint resistance. We produce numerous sample joints and measure time- and thermal cycle-dependent resistance, and characterize the joints using x-ray and other analysis tools. For a subset of the joints, we use SEM/EDS to try to understand the physical and chemical processes that effect joint behavior.
Coated conductors (CCs) have emerged as the dominant wires for HTS applications such as power cables, rotating machines and magnets. However they present a complicated heat load while carrying transport currents in external alternating magnetic fields, because power dissipates in the form of not only magnetisation loss, but also dynamic loss (transport loss). This makes accurate predictions of both the losses necessary to the design of reliable HTS devices.
Existing research estimates dynamic loss via analytical method and experimental measurement. However, no work has been done to analyse dynamic loss simultaneously with magnetisation loss, and clarify their different but interlinked characteristics.
This paper presents detailed and systematic results to clarify dynamic loss and magnetisation loss in CCs. Both modelling and experimental measurements of CCs were carried out in alternating magnetic fields up to 100 mT. The results show that CCs exhibit dynamic loss when external magnetic field exceeds certain threshold strength, while magnetisation loss exists all the time. Both losses increase significantly along with the increasing external magnetic field. Results also clearly demonstrate how dynamic and magnetisation losses form, how these losses can be distinguished from each other, and how these losses are affected by transport current and magnetic field. The work will greatly benefit the accurate predictions of complicated losses and ensure reliable HTS applications.
Acknowledgements:
This work is supported by Startup Grant (531NPG) and Opening Project Grant of State Key Laboratory of Electrical Insulation and Power Equipment (EIPE16203).
When coated conductors are assembled into a large-current cable such as Roebel cable or CORC cable, their electromagnetic behaviors are much more complicated than a single coated conductor: imbalance of strand-inductances might cause a non-uniform current distribution among coated conductors; the electomagnetic behavior of each coated conductor should be influenced by others. In this presentation, we focus on the electomagnetic behavior of each coated conductor in large-current cables. Current distributions in coated conductors are far from uniform. The non-uniform current distributions affect the field qualities of magnets. The temporally-changing current distributions cause ac losses. Electromagnetic field analyses are carried out for coated conductors assmebled into a large-current cable such as CORC cable and Roebel cable in order to clarify the influences of the cable geometries on the electromagnetic behaviors of coated conductors. The effect of striation is studied for large-current cables as well as simple models of stacked striated coated conductors.
This work was supported by Japan Science and Technology Agency under Strategic Promotion of Innovative Research and Development Program (S-Innovation Program).
A 9-tape (14mm width pre-cut, 4.9 mm post-cut) REBCO Roebel cable from Robinson Research Institute had MQE measured in a LHe bath at varying I/Ic in applied fields up to 12 Tesla. Quench was initiated using a 4.5 mm by 4.5 mm Nichrome film heater. Current sharing was monitored throughout the cable using transverse voltage taps and Tmax of the quench was measured with calibrated Type-E thermocouples. These measurements are part of a larger effort to understand stability in REBCO Roebel cables.
The physics behind Stirling-type cryocoolers are complicated. One dimensional simulation tools only offer limited details and accuracy, in particular for cryocoolers that have non-linear configurations. Multi-dimensional Computational Fluid Dynamic (CFD) methods are useful but are computationally expensive in simulating cyrocooler systems in their entirety. In view of the fact that some components of a cyrocooler, e.g., inertance tubes and compliance tanks, can be modeled as 1-D components with little loss of critical information, a 1D-3D coupled model was developed. Accordingly, one-dimensional – like components are represented by specifically developed routines. These routines can be coupled to CFD codes and provide boundary conditions for 2D/3D CFD simulations. The developed coupled model, while preserving sufficient flow field details, is two orders of magnitude faster than equivalent 2D/3D CFD model. The predictions of the model show very good agreement with experimental data and 2D/3D CFD simulations.
Thermodynamic and fluidic modeling results for a novel small satellite (SmallSat) Stirling Cryoooler, capable of delivering up to 400 mW net cooling power at 80 K for less than 6 W DC input power, are discussed in this paper. Industry and government requirements for SmallSat borne infrared sensors is driving the development of ever-more miniaturized cryocooler systems. Such cryocoolers must be extremely compact and lightweight, a challenge met by this research team by operating a Stirling cryocooler at a frequency of approximately 300 Hz. The primary advantage of operating at such a high frequency is that the required compression and expansion swept volumes is reduced relative to linear coolers operating at lower frequencies, which evidently reduces the size of the motor mechanisms and the thermodynamic components. In the case of a pulse tube cryocooler, this includes a reduction in diameter of the pulse tube itself. This unfortunately leads to high boundary layer losses, as the presented results demonstrate. Using a Stirling approach with a mechanical moving expander piston eliminates this small pulse tube loss mechanism, but other challenges are introduced, such as maintaining very tight clearance gaps between moving and stationary elements. These challenges and how they are being overcome are also discussed.
Methane is one of the major volatile components of the natural gas. With the heat load, the low boiling components tend to evaporate first and is likely to build up the pressure in the storage vessel. In order to avoid such situation, the storage vessel is generally vents out the vapour to the atmosphere. If this vapour can be re-condensed in-situ at storage pressure, it will save Methane from escaping to the atmosphere and thereby also ensure reduction in the pollution level. Small capacity storage systems will need small capacity coolers providing the cooling around 130 K. Closed cycle Stirling cryocooler is one of the choices. If the performance of the same is further enhanced at the desired temperature level by some means, it will obviously make Stirling coolers a more preferred option. In 2000, Bapat explained theoretically, the improvement in cooling capacity around liquid Nitrogen temperature (≅ 80 K) using second order cyclic analysis with a condensable component, Nitrogen in the regular working fluid, Helium. This paper presents the performance estimates of Methane being used as the condensable fluid with Helium as the regular non-condensable component in the working fluid. A substantial improvement in the cooling capacity and also the COP of the cooler is predicted using second order cyclic analysis. This does not involve any changes in the hardware of the system. While the cooling capacity increases to more than two times, the work input is marginally reducing till the temperature is increased to about 150 K. It may be possible to replicate the results in larger capacity Stirling units which uses Helium as the working fluid, at normal working pressures of the system.
High cooling power (i.e., from several hundred Watt to thousand Watt) free piston Stirling cryocooler could find important application in fields such as boil-off gas recondensation and superconducting. This work reveals the acoustic field characteristics mainly concerning the regenerator and acoustic impedance match between cooler and linear compressor. Based on thermoacoustic theory, parameter sensitivity and physical mechanisms behind are clearly shown. A further step toward experimental validation is carried out by monitoring some key parameters, including dynamic pressure, acceleration, current, voltage, etc. The good agreement between experiments and calculations is beneficial to a better understanding. So far, a cooling power of 350 W at 80 K has been achieved, corresponding to an acoustic-to-cooling efficiency of 35% of Cannot and the electric-to-acoustic efficiency reaches 82%.
Free-piston Stirling crycooler, featuring its elimination of the motor that drives the displacer, has extensive applications in various areas for its simplicity in structure and decrease in mass. However, the elimination of the motor has not only added to the complexity of its analysis and design, but also made it differ from Stirling cryocoolers with displacer driving mechanism, such as the integral type and Oxford type, in thermodynamic characteristic. Therefore, an idealized mathematical model has been established and an attempt has been made to analyze the thermodynamic characteristic of free-piston Stirling cryocooler in an analytical approach with this model. To certify the mathematical model, comparison has been made between the results obtained by the model and by a commercial software, which indicates that the two results tend to get closer and closer as more complicating factors are removed from the model in the commercial software. This mathematical model reveals that due to the displacer damping which is necessary to the production of cooling capacity, the COP of free-piston Stirling crycooler base on various idealized assumptions is always lower than that of Stirling cycle, or Carnot cycle. Also, conditions that maximize the cooling capacity are studied in detail with the mathematical model, which reveals the characteristics of an optimized free-piston Stirling crycooler. By excluding all the complicating factors, the idealized mathematical model sheds light on the thermodynamic nature of free-piston Stirling crycooler, and provides an essential reference for its design and optimization.
Construction and installation of the FRIB 4.5 K helium refrigeration system is nearing completion, with compressor system commissioning and 4.5 K refrigerator commissioning on schedule to occur in 2017. The LINAC 4.5 K helium distribution system, all major process equipment, and the cryogenic distribution for the sub-systems have been procured and delivered. The sub-atmospheric cold box fabrication is planned to begin the summer of 2017, which is on schedule for commissioning in the spring of 2018. Commissioning of the support systems, such as the helium gas storage, helium purifier, and oil processer is planned to be complete by the summer of 2017. This paper presents details of the equipment procured, installation status and commissioning plans.
RAON is a rare isotope beam facility being built at Daejeon, Korea. The RAON consists of three linear accelerators, SCL1 (1st SuperConducting Linac), SCL2, and SCL3. Each linac has its own cryogenic plant. The cryogenic plant for SCL2 will provide the cooling for cryomodules, low temperature SC magnets, high temperature SC magnets, and a cryogenic distribution system. This paper describes the specification of the plant including cooling capacity, operation modes, transient operation modes, and operating time. In order to reduce CAPEX with the specification, two suppliers will consider no liquid nitrogen pre-cooling, one integrated cold box, and one back-up HP compressor. The detail design for the plant can be started at the end of this year.
The JT-60SA cryogenic system is the French voluntary contribution to the joint European - Japanese project JT-60SA, a superconducting tokamak currently under assembly at the Naka Fusion Institute of QST in Japan. The tokamak will achieve deuterium plasmas with typical flat top durations of up to 100 seconds. Procurement of the cryogenic system was managed by CEA. The technical specification was issued by CEA in close cooperation with F4E and QST, according to the different operating scenarios of JT-60SA. The specifications considered also the results of a dedicated R&D program at CEA, to explore the conditions for a safe and economical operation of the cryogenic system with demanding pulsed loads.
The cryoplant was contracted to Air Liquide Advanced Technologies (AL-aT), France. Most of the subsystems were manufactured in Europe, shipped to Japan and finally installed at Naka. After one year of commissioning, the acceptance tests were successfully completed in October 2016 in close collaboration between QST, F4E, CEA and AL-aT. The ownership of the plant was transferred to QST end of 2016.
The cryogenic system has different cryogenic users at various temperatures: the superconducting magnets at 4.4 K, the current leads at 50 K, the thermal shields at 80 K and the diverter cryo-pumps at 3.7 K. The cryogenic system has an equivalent refrigeration power of about 9.5 kW at 4.5 K, with peak loads up to 12 kW caused by the nuclear heating, the eddy currents in the structures and the AC losses in the magnets during cyclic plasma operation.
The acceptance test scenarios and the transitions between different operation modes were performed by automated sequences. The main results of the acceptance tests will be reported, with emphasis on the management of the challenging pulsed operation using a liquid helium volume of 7 m³ as thermal damper.
Many existing and future nuclear fusion reactors rely on superconducting (SC) magnets to confine the plasma. In order to maintain their properties, these magnets must be cooled to very low temperatures (~5 K) and a complex and expensive cryogenic system, adopting He as principal process fluid, is needed.
Here a model of the He refrigerator of the ITER Central Solenoid Model Coil (CSMC), installed at the National Institutes for Quantum and Radiological Science and Technology, Naka (Japan), is developed. The model allows to analyze and, if needed, optimize long transients, such as the cool down (CD) of the SC magnets from ambient to cryogenic temperature.
The model components are developed according to the design data from the thermodynamic cycle of the refrigerator selected as reference, which features a configuration typical of many existing SC magnets facilities and tokamaks. The object-oriented Modelica programming language has been used, already adopted for the cryogenic circuit module of the 4C code, developed in recent years by our group for the thermal-hydraulic analysis of transients in SC coils. The model of each component of the refrigerator, described in the paper, has been independently tested and then added to the existing “Cryogenics” Modelica library.
The refrigerator model resulting from a suitable assembly of components is presented in the paper and the results of a CD simulation are reported, showing a good agreement with the temperature, pressure and mass flow rate evolutions measured during the transient at different locations inside the refrigerator, within the uncertainties due to the manual operation of the facility.
The ITER cryoline (CL) system consists of 37 types of vacuum jacketed transfer lines which forms complex structured network with a total length of about 5 km spread inside the Tokamak building, on a dedicated plant bridge and in cryoplant building/area. One of them, low pressure relief line recovers helium discharged from the process safety relief valves of the different cryogenic users in the tokamak as well as cryoplant buildings and sent it back to the cryoplant via heater and recovery system. The process pipe diameters of the relief line vary from DN 50 to DN 200 and the length of the line is more than 1500 m.
Site Power Failure or Loss of Cooling Power (LOCP), Loss of Vacuum in the Cryostat (Cr LIV), Loss of Vacuum in the Vacuum Vessel (VV LIV), Loss of Insulation Vacuum (LIV) for Cryoline or Auxiliary Cold Boxes (ACBs) are main scenarios for discharging gas in the relief line. In order to analyze integrated behavior of the relief line under these events, dynamic mathematical models prepared in EcosimPro® is used. LIV of the CL is one of the worst scenarios apart from LIV in ACBs. Torus and Cryostat Cryoline is chosen to simulate the virtual LIV and to study the anticipated behavior of the relief line. Both helium LIV and Air LIV (with and without fire) have been simulated during this study.
After the brief description of the CL system, the paper will describe the EcosimPro® model prepared for the dynamic study. The paper will also describe the results like minimum temperature of relief line, mass flow and maximum pressure in the relief line which are essentially used to choose the type and location of safety relief devices to protect the CL process pipes.
The central solenoid magnet forms the heartbeat of the International Thermonuclear Experimental Reactor (ITER). The 12.8 meter high magnet will consist of six solenoid modules, each weighing 110 tonnes. General Atomics is currently fabricating these modules under a contract managed by the US ITER Project Office at Oak Ridge National Laboratory, sponsored by the Department of Energy’s Office of Science. Cold testing of the individual modules requires a dedicated cryogenic system providing the required refrigeration capacities at conditions similar to those the modules will experience during operation.
In 2014, Linde Cryogenics was awarded a contract for the engineering, procurement, fabrication and commissioning of this dedicated system. The system is based on the Linde Standard LR-Series which has a capacity of 900W at 4.5K. This is coupled to a secondary supercritical refrigeration loop within the same coldbox. A Linde cold circulator pump recycles 4.7K helium at 5.5 bar through the module under test at up to 320 gm/sec. One critical item of the testing is the cool-down process of the module within a very narrow temperature band and heat loads of up to 13 kW.
The presentation will show the key features of the overall system and highlight some commissioning results.
The need of cooling devices that are lightweight, low powered, physically flexible, easily manufactured and most importantly exhibit high heat transfer rates are requirements that space agencies demand in a cooling system. Therefore, Pulsating Heat Pipes (PHPs) are being extensively investigated to provide these requirements. This paper summarizes the current development of cryogenic Pulsating Heat Pipes with single and multiple evaporator sections built and successfully tested at UW-Madison. Recently, a Helium based Pulsating Heat pipe with three evaporator and three condenser sections has been operated at fill ratios between 20 % and 90 % operating temperature range of 2.9 K to 5.19 K, resulting in a maximum effective thermal conductivity up to 50,000 W/m-K. In addition, a Nitrogen Pulsating Heat Pipe has been built with three evaporator sections and one condenser section. This PHP achieved a thermal performance between 32,000 W/m-K and 96,000 W/m-K at fill ratio ranging from 50 % to 90 %. Split evaporator sections are very important in order to spread cooling throughout an object of interest with an irregular temperature distribution or where multiple cooling locations are required. Hence this type of configurations could be applied to cryo-propellant tanks, superconducting magnets and photon detectors.
The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will increase the accelerator’s luminosity by a factor 10 beyond its original design value, giving rise to more intense collisions and generating an intense flow of debris as a consequence. A new design of the beam screen for the inner triplets, incorporating tungsten alloy blocks, has been developed to shield the superconducting magnets and the 1.9 K superfluid helium bath by reducing the impact from the incoming radiation.
The HL-LHC beam screens will operate at a higher temperature range (from 60 K to 80 K as opposed to 4.6 K to 20 K for the LHC beam screens) and are designed to sustain a nominal head load of 15 W/m, over 10 times the nominal heat load for the original LHC design. As such, heat transfer studies are needed to characterise the performance of all major thermal pathways of the proposed beam screen as well as the conductivity of the individual components and the conductance across the respective interfaces.
A parametric study of representative samples of the beam screen was carried out to assess the influence of several parameters such as the compression force between the tungsten block and the beam screen and the heatsinking of the blocks to the cooling source. This study was performed using a thermal conductivity test stand based on an adapted two-stage pulse tube refrigerator which allows for precise temperature measurements along the different components of the beam screen under varied heat loads. Results of this study are presented and compared to thermal simulations, and its impact on the final design is discussed.
As applications of superconducting logic technologies continue to grow, the need for efficient and reliable cryogenic packaging becomes crucial to development and testing. A trade study of materials was done to develop a practical understanding of the properties of interface materials around 4 K. While literature exists for varying interface tests, discrepancies are found in the reported performance of different materials and in the ranges of applied force in which they are optimal. In considering applications extending from top cooling a silicon chip to clamping a heat sink, a range of forces from approximately 10 lbs to approximately 100 lbs was chosen for testing different interface materials. For each range of forces a single material was identified to optimize the thermal conductance of the joint. Of the tested interfaces, indium foil clamped at approximately 100 lbs showed the highest thermal conductance. Results are presented from these characterizations and useful methodologies for efficient testing are defined.
The work detailed here describes how a novel approach has been applied to overcome the challenging task of cryo cooling first crystals of many of the world’s Synchrotrons’ more challenging beam lines. The beam line configuration investigated in this work typically requires the crystal to diffract 15 Watts of 8.27x10-11m wavelength X rays and dissipate the additional 485 watts of redundant X ray power without significant deformation of the crystal plains. In this case the beam foot print is 25mm by 25mm on a crystal surface measuring 38mm by 25mm and is required to maintain a radius of curvature of less than 50km. Currently the crystal is clamped between two copper heat exchangers which have LN2 flowing through them. The crystal needs to be clamped strongly enough to prevent thermal deformation developing and at the same time loosely enough to not instigate mechanical strains and deformation. An additional source of error also occurs as the configuration is assembled by hand, leading to human error in the assembly procedure
This new approach explores making the first crystal cylindrical with a sleeve heat exchanger. By manufacturing the copper sleeve to be a push fit at room temperature the sleeve can be slid over the silicon and when cooled will form an interference fit. This has the additional advantage that the crystal and its heat exchanger become a single entity and will always perform the same way each time it is used, eliminating error due to assembly. Various fits have been explored to investigate the associated crystal surface deformations under such a regime. In addition this methodology is also being explored as a method of overcoming sealing issues for direct cooling of first crystals.
Abstract:
Cryocoolers have been widely used for cooling down the superconductors, cells, cryogenic liquid storage tanks, etc. Since they can only operate vertically, and provide cooling at cold heads, it is difficult to be utilized in distributed cooling and long-distance systems. It can be achieved by a more flexible and high-efficiency heat transfer method connecting cryocoolers and objects. As for that, pulsating heat pipe (PHP) is regarded as a great solution because of its flexible structure and excellent performance. The experiments on PHPs with cryogenic fluids have been carried out, indicating their efficient performances in cryogenics. There are large differences in physical properties between the fluids in room and cryogenic temperature, resulting in their different heat transfer and oscillation characteristics. Up to now, the numerical investigations on cryogenic fluids have not been reported. In this paper, the model of the closed-loop PHP with multiple liquid slugs and vapor plugs is performed with nitrogen and hydrogen as working fluids, respectively. Further, the effects of gravity, surface tension and heating wall temperature on the performance of close-looped PHP with Nitrogen and Hydrogen are also investigated.
ACKNOWLEDGEMENTS:
This work is supported by the National Natural Science Foundation of China (Grant No. 51506040), University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province (UNPYSCT-2015050), and a Project of Shandong Province Higher Educational Science and Technology Program(J16LJ56)
1 Corresponding author: jiaobo@hrbust.edu.cn
Raising critical current density Jc in high temperature superconductors, such as YBa2Cu3O7 or RE-123 films, is important to performance-cost balanced conductor technology for commercialization. Development of strong nanoscale artificial pinning centers (APCs) in RE-123 films has led to significantly raised Jc in APC/RE-123 nanocomposites by enhanced pinning on magnetic vortices in moderate to high magnetic fields towards that demanded in practical applications. The effort in controlling the morphology, dimension, orientation, and concentration of APCs raises a fundamental question on how strains interact at microscopic scales in determining the APCs quantitatively. Answering this question demands an interactive modeling-synthesis-characterization approach towards a thorough understanding of fundamental physics governing the strain-mediated self-organization of the APCs in the APC/RE-123 nanocomposites.
The paper reports our recent work in controllable generation of APCs towards strong and isotropic pinning using the interactive modeling-synthesis-characterization approach.1-7 Three specific methods were explored on 1D APC/RE-123 nanocomposites using: (1) lattice mismatch substrates to promote 1D APC splay; (2) impeded alignment of 1D APC of high-concentration using a secondary APC; and (3) low-temperature quench of long-length 1D APC growth. We show enhanced isotropic pining attributed to APC landscape of mixed morphologies that not only benefit pinning at different H orientations but also reduce the detrimental effect on superconductivity by the train on the RE-123 matrix.
An industrial R&D programme is ongoing at SuperOx, aimed at improving 2G HTS wire performance in magnetic field. We introduce perovskite artificial pinning centres into the HTS layer matrix. In contrast to most studies described in the literature, we use the high rate production processing parameters and PLD equipment at SuperOx Japan. This paper reports the results of Phase 1 of this programme.
We fabricated 2G HTS wires using GdBCO PLD targets with 0-7% (wt.) BaZrO3 or BaSnO3 at 100, 150 and 200 Hz frequency. The crystal structure and texture parameters of the HTS layer and perovskite inclusions were characterised with XRD. The HTS layer microstructure and morphology were studied with TEM. The angular dependencies of the critical current of the samples were measured by 4-probe transport technique at 77 and 65 K in 1 T magnetic field and derived from magnetic hysteresis curves measured in PPMS in the 4.2-77 K temperature range and 0-9 T magnetic field range.
BaZrO3 and BaSnO3 formed column-shaped semi-coherent nano-inclusions in the GdBCO film matrix. The typical transverse size of the nano-columns was about 5 nm, and their volume density correlated with the dopant concentration. All doped samples exhibited much lower angular anisotropy of in-field critical current and higher lift factors than undoped samples. Doped samples demonstrated higher minimum critical current for all field orientations than undoped samples at 65 K and at lower temperatures.
These results are an encouraging start of our programme, as they show a positive impact of artificial pinning centres introduced into 2G HTS wires fabricated at production throughput. Future work will be focussed on the optimisation of PLD growth parameters, in order to maximise the improvements in specific temperature and field conditions, as well as on the verification of reproducibility of the improvements in production wires.
Strong and isotropic vortex pinning landscape is demanded for high field applications of high temperature superconductor (HTS) thin film. Double-doping (DD) of different kinds of artificial pinning centers (APCs) has been identified as a promising approach to generate such a pinning landscape. This work presents a systematic study on the critical current density Jc(H, $\theta$) of 3%Y2O3+2-6 vol.% BZO (BZO DD) and 3%Y2O3+ 2-6 vol.% BHO (BHO DD) films deposited at their optimal growth conditions. The goal is to elucidate the effect of the secondary APC Y2O3 nanoparticles on the alignment of the BZO and BHO nanorods of comparably diameters and the consequent Jc (H, $\theta$) behavior. Intriguingly, a much enhanced isotropic pinning was observed in BHO DD samples. For example, at 65 K and 9T, the variation of the Jc across the entire $\theta$ range from $\theta$=0 (H//c) to $\theta$=90 degree (H//ab) is less than 18 % for BHO DD film, in contrast to about 100% for the BZO DD counterpart. Since the two samples have comparable Jc values at H//c and the larger Jc variation in the latter is primarily caused by the reduced Jc in the larger $\theta$>40 deg especially at $\theta$=90 deg (H//ab), the improved isotropic pinning in the BHO DD samples illustrates the higher tunability of the APC microstructure using secondary APCs.
After 25 years of development, several high-temperature superconductors (HTS) are becoming engineering materials commercially available as long-length wires. Among them, REBa2Cu3O6+y (REBCO, RE rare earth) compounds have emerged as excellent candidates for the manufacture of superconducting Coated Conductors (CCs) due to their high-field current carrying capacity. REBCO nanocomposites, based on the introduction of nanometric non-superconducting secondary phases in the superconducting matrix, have appeared as interesting materials to improve the superconducting properties and pinning performances in a wider range of applied magnetic fields and temperatures.
Chemical solution deposition (CSD) has been demonstrated to be a scalable, versatile and cost-effective technique for in-situ preparation of REBCO thin films with embedded oxide secondary phases, starting from a complex metalorganic precursor solution. In such films, the nanoparticles tend to randomly orient in the REBCO matrix creating a high density of secondary defects which generate a nanostrained REBCO matrix that ultimately lead to a strong enhancement of the isotropic pinning contribution.
In this work, we present the superconducting properties of (Y/Gd)BCO+12 mol% BaHfO3 nanocomposite films deposited on single crystals (SrTiO3) and on buffered tapes. After a complex growth-parameter optimization for different Y/Gd ratios, we have been able to obtain high-quality films on both kinds of substrates. Large critical current densities (Jc = 7 MA/cm2) and pinning forces (Fp = 16 GN/m3) are achieved e.g. for a 220 nm GdBCO+12%mol BaHfO3 film on SrTiO3, values among the highest in literature. Also, 1 micron thick films were prepared showing an excellent texture and large values of critical current (Ic). Finally, the results we obtain working with the buffered tapes demonstrate that our approach is very promising for future industrial application since we were able to grow films that present similar features than the ones obtained in single crystals.
Pinning centers have been introduced into (Gd,Y)BCO to increase critical current density, Jc, for applications. However, in addition to generating high magnetic fields (by possessing high Jc in the magnet windings), magnets used in accelerators should generate homogeneous and time-invariant magnetic fields. Flux creep has been shown to be significant in high temperature superconductors even at low temperatures, and thus it may cause the magnetic field of the magnet to drift with time. In this work, the influence of Zr additions, to YBCO tape, on the magnetic Jc and flux creep were studied. Magnetic Jc at 4.2 K, determined by measuring the M-H out to 14 T, and flux creep was studied in three different (Gd,Y)BCO tape samples. The samples had Zr additions of 0, 7.5, and 25 mol.%. The addition of Zr increased magnetic Jc, and also decreased the amount of creep in the samples. The decreased creep result suggests that the Zr addition creates pins with deep potential wells, as compared to creating many pins with shallower potential wells. Pinning potential vs current density (U(J) vs J) curves were generated using creep results at 8 different temperatures: 4.2, 10, 20, 30, 40, 50, 60, and 77 K. The creep was measured over 1800 seconds at 7 different fields: 12, 10, 8, 6, 4, 2, and 1 T. The pinning potential was compared to pinning potentials determined in previous YBCO experiments which studied other pinning center additions. Transmission electron microscopy was used to study the size and distribution of the pinning centers.
Nb3Sn superconducting wires have been developed for nearly half a century and their record Jcs have plateaued since the early 2000s. The only opportunity for further significantly improving Jc of Nb3Sn conductors relative to the present state of the art lies in improving flux pinning capacity. In this talk efforts to improve pinning of Nb3Sn conductors by introducing additional pinning centers (APC) are reviewed, and it is seen that due to the critical processing requirements of Nb3Sn wires, the most promising approach is an internal oxidation technique that forms inter-granular and intra-granular ZrO2 nano particles in Nb3Sn wires, which can significantly refine Nb3Sn grain size. This not only causes enhancement of maximum pinning force Fp,max, but also causes the peak of Fp-B curves to shift to higher fields as grain size is refined to a certain level. Methods to implement this technique in practical Nb3Sn wires are introduced, and its significant benefit on Jc of Nb3Sn conductors is shown.
The 1987 discovery of high-TC superconductivity in ceramic materials at temperatures around 90K set off a frenzy of research in the development of high-TC electronics,motivated by the prospects of electronics operating in liquid nitrogen at 77K opposed to 4K liquid helium. Unfortunately, researchers soon discovered that these new materials were much more difficult to process than conventional metal superconductors. High-TC materials are very anisotropic and the superconducting properties vary along the different crystallographic directions which complicates manufacturing of the basic building blocks of superconducting electronics: Josephson junctions. Furthermore, the length scale of superconductivity in high-TC ceramics is very short compared to low-TC metals. Despite these challenges many high-TC Josephson junction manufacturing
techniques have emerged over the last three decades but none is able to generate large numbers of junctions with predictable characteristics necessary for large scale circuits. Recently, my group has demonstrated a new scalable nanomanufacturing method of high‐TC electronics using the finely focused beam from a helium ion microscope, which has the potential to deliver large numbers of high-quality circuits while at the same time reducing their costs by orders of magnitude. I will present some of the novel characteristics and applications of this new remarkable technology ranging including biomedical sensors for neural imaging and advanced wide bandwidth electrically small antennas.
We have fabricated Josephson junctions and arrays with a focused helium ion beam from Y-Ba-Cu-O, a high temperature superconductor. The Josephson junction is the fundamental building block of most superconducting electronics. Normally the size of a junction is chosen to be less than the Josephson penetration depth (λJ) ~4 µm, a fundamental length scale for superconducting devices, because it ensures that the supercurrent is distributed evenly throughout the junction. For a static current biased Josephson junction or array of junctions, the voltage across the device modulates in a magnetic field. The voltage as a function of magnetic field (V-B) of an ideal Josephson junction goes as |sin(B×A)/(B×A)|.Where B×A is the product of applied magnetic field B and junction area, A. When the length of a junction becomes larger than λJ, the V-B comes more triangular and asymmetric. As a result, this improves the linearity of the Josephson based voltage magnectic field transducing devices. In addition, the skewing of the V-B makes one side of the peak extremely sharp that enhances the sensitivity (dV/dB*) to detect small fields.
In our work, we will present the fabrication process and measurement results of Josephson junctions and arrays with widths that range from 1 micron to 30 microns. These devices were fabricated with 30 nm Y-Ba-Cu-O films grown by reactive coevaporation. After patterning the large features and electrodes of the devices with standard photolithography and Ar ion beam etching, the junctions were directly written using a 30 keV focused helium ion microscope with doses of 1016~1017 ions/cm2. Our results show that Josephson junctions and arrays have great potential for large dynamic range for advanced magnetic antennas for communications.
* Cybart, Shane A., et al. "Nano Josephson superconducting tunnel junctions in YBa2Cu3O7–δ directly patterned with a focused helium ion beam." Nature nanotechnology 10.7 (2015): 598-602.
We study the coherent terahertz emission from the intrinsic Josephson junctions in thermally-managed, high-symmetry, thin microstrip antennas constructed from single crystals of the highly two-dimensional, layered high-temperature superconductor BSCCO. The thin antennas studied are disk[1,2], square[3], and equilateral triangular[4,5] in shape. Upon application of a dc voltage across the junctions, the primary radiation source is the uniform ac Josephson current, but when the appropriate point in the current-voltage characteristics is found, the excitation of an electromagnetic cavity mode can lead to a considerable enhancement of the output power. When properly thermally managed by convering the top and bottom of a thin BSCCO crystallite with Au and sandwiching that between sapphire plates[6], only the one-dimensional representation wave functions of the appropriate point groups are excited, and the world record 2.4 THz emission from a superconductor was recently observed[2] from such a device. The coherent emission is widely tunable and has a narrow linewidth. The angular distributions of the output power are calculated and compared with experiment.
[1] M. Tsujimoto et al., Phys. Rev. Lett. 105, 037005 (2010).
[2] T. Kashiwagi et al., Appl. Phys. Lett. 107, 082601 (2015).
[3] R. A. Klemm et al., IEEE JSTQE (2017, in press).
[4] D. P. Cerkoney et al., J. Phys.: Condens. Matter 29, 015601 (2017).
[5] K. Delfanazari et al., Opt. Express 21, 2171 (2013).
[6] T. Kashiwagi et al., Phys. Rev. Applied 4, 054018 (2015).
It is well established that superconducting materials will emit microwave/terahertz radiation when illuminated with a femtosecond infrared laser pulse. Typically this phenomena is examined by illuminating a voltage biased superconducting thin film bridge. In this investigation an inductively charged superconducting thin film ring is considered. We believe the configuration lends itself to a simple compact microwave emitter device as the antenna plays the part of the waveguide and power supply, and contact heating between the current leads and the superconductor are now eliminated. We find that the emitted energy of this system displays a power-law dependence with increasing current, laser energy and illumination area, and shows a frequency dependence on the system dimension as well as a well-defined polarization direction. Results illustrate the rich and complex dynamics that span the optical, terahertz and microwave regimes.
This paper introduces a Software Development Kit (SDK) that enables the creation of custom software applications that automate the control of a cryo-refrigerator (Quantum Design model GA) in third party instruments. The SDK was developed using C# in the .NET framework, utilizing a polymorphic design. It provides an easy to user interface for controlling compressor functions, without the need of in-depth knowledge of low level controls. This package also provides a Dynamic Link Library (DLL) and a Graphical User Interface (GUI) application for a more streamlined end user experience.
A remote interface allows real time tracking and logging of critical system diagnostics such as pressures, temperatures, valve states and run modes. The helium scroll compressor speed and Gifford-McMahon (G-M) cold head speed can be manually adjusted over a serial communication line. This configuration optimizes cooling power, while reducing wear and vibration of moving components thus extending service life. Additionally, a proportional speed control mode allows for automated throttling of speeds based on temperature or pressure feedback from a 3rd party device. Warm up and cool down modes allow 1st and 2nd stage temperatures to be adjusted without the use of external heaters.
The regenerator is a critical component of all Stirling and Pulse Tube cryocoolers. It generally consists of a microporous metallic or rare-earth filler material contained within a cylindrical shell. The accurate modeling of the hydrodynamic and thermal behavior of different regenerator materials is crucial to the successful design of cryogenic systems. Previous investigations have used experimental measurements at steady and periodic flow conditions in conjunction with pore-level CFD analysis to determine the pertinent hydrodynamic parameters, namely the Darcy permeability and Forchheimer coefficients. Due to the difficulty associated with experimental measurement at cryogenic temperatures, past investigations were mostly performed at ambient conditions and their results are assumed to be appropriate for cryogenic temperatures. There is, however, a pressing need to determine the hydrodynamic parameters for several regenerator materials under prototypical conditions and verify the validity of the foregoing assumption. In this study, regenerators filled with woven screen matrices such as 400 mesh T316 stainless steel were assembled and experimentally tested under periodic helium flow at cryogenic temperatures. The mass flow and pressure drop data were analyzed using Sage cryocooler modeling software and ANSYS Fluent to determine the dimensionless friction factor, Darcy Permeability and Forchheimer coefficients. These results are compared to previous investigations at ambient temperature conditions, and the relevance of room-temperature models and correlations to cryogenic temperatures is critically assessed.
Large GM cryocoolers (>300W at 80K) have been used for many high temperature superconductors and various other cryogenic devices. This paper presents the improvement of a GM cryocooler, Cryomech model AL600, which has nominal cooling capacity of 600W at 80K. The cooling performance and vibrations of the AL600 cold head have been studied. The cold head seals, regenerator and heat exchanger as well as operating parameters were optimized to increase the cooling capacity. The bottom temperature was reduced from 26.6 K to 22.1 K. The cooling capacity was improved from 615 W at 80 K to 700W at 80 K with a power input of 12.5 kW. It has the highest Percent Carnot Efficiency at 15.3% and the largest cooling capacity of any available GM cryocoolers to date. The vibration of AL600 was analyzed theoretically and experimentally. The new displacer bumper design reduced the vibration force on the room temperature flange from 170 lb to 11 lb. This new generation AL600 GM cryocooler will be more attractive for many applications.
To improve the efficiency of a cryocooler, an effective way is to improve the efficiency of the regenerator. In general, the heat capacity of materials decreases as temperature decreases. Thus, when temperature is below 40 K, lead or bismuth spheres are often used as a regenerator material. However, the pressure drop in a sphere regenerator is much larger than that in a screen regenerator. To overcome this dilemma, Xu, et al reported a tin-plated screen in ICEC-ICMC 2016. However, the reliability of tin at low temperature is still not fully verified since there is a phase transition from α to β, which may result in a reduction of mechanical strength. In this paper, another candidate, zinc-plated screen, is proposed. A comparison test was performed with a two-stage GM cryocooler by replacing part of the first stage regenerator material, phosphorus bronze screens with zinc-plated screens. Compared to a regenerator filled with bronze screens, the cooling capacity of the first stage increased by about 11% at 40 K and 60% at 30 K with such zinc-plated screens. The detailed experimental results will be reported in this paper.
Pulse tube refrigerator (PTR) is a type of regenerative gas-cycle refrigerator which operates with oscillating pressure and mass flow gases such as helium, argon, and nitrogen. As the key part of PTR, regenerator works as a heat reservoir in which oscillating gas flow rejects or absorbs heat into or from the solid matrix. A proper description of the flow characteristics and heat transfer of in the regenerator is crucial for modeling the PTR performance. In this paper, a one-dimensional model based on Lagrangian representation is developed to simulate the oscillating flow in the regenerator of the high-frequency PTR. The continuity equation, momentum equation and energy equation are solved iteratively using SIMPLER algorithm. The Darcy-Brinkman-Forchheimer model is used in the momentum equation, and a thermal non-equilibrium model is implemented in the energy equation. Lagrangian representation is used to describe the thermodynamics of fluid parcels while the Eulerian representation (control volume method) is used for the energy equation of the solid matrix. Periodic flow of sine function is used as the boundary condition. The numerical results are compared with the experimental data, which shows good agreement for the mass flow at the cold end. The thermodynamic parameters of the gas parcels are obtained which reveals the critical processes of the heat transfer in the regenerator under high-frequency oscillating flow. The performance of regenerator with different geometries is evaluated based on the numerical results, and optimization is performed in order to achieve desired performance. This numerical study provides insight for understanding the physical process in the regenerator of the high-frequency PTR, and the proposed model can serve as a useful tool for the design and optimization of cryogenic regenerator.
For a multi-stage pulse tube refrigerator, improving the regenerator efficiency is the most important thing. A solid phase-shifter can get higher operating pressure ratio compared with inertance tube. The pressure ratio influence on the performance of the regenerator is discussed. The result shows that for a given regenerator, there is an optimum pressure ratio to get best performance.
This report presents and discusses the results of repeatability experiments gathered from the multi-layer insulation thermal conductivity experiment (MIKE) for the measurement of the apparent thermal conductivity of multi-layer insulation (MLI) at variable boundary temperatures. Our apparatus uses a calibrated thermal link between the lower temperature shield of a concentric cylinder insulation assembly and the cold head of a cryocooler to measure the heat leak. In addition, thermocouple readings are taken in-between the MLI layers. These measurements are part of a two-phase NASA-Yetispace-FSU collaboration to better understand the repeatability of thermal conductivity measurements of MLI. During both phases of testing, the cold boundary was maintained at 77±3 K, and warm boundary at 293±2 K for a duration of four hours at a steady state variance of less than 0.1 K/hr on both cylinders. Temperatures from three Cernox® temperature sensors on each of the two cylinders are averaged to determine the boundary temperatures. A high vacuum, less than 10-5 torr, is maintained for the duration of testing. Yetispace fabricated five identical MLI blankets with twelve layers for each phase with dimensions matching our testing rig. A temperature profile across the MLI is generated. Layer density varied from 19.9 – 26.0 layers/cm. The average measured heat load was 2.40±0.31 W for phase-one and 2.92±0.47 W for phase-two. This suggests there is a high variance of MLI performance. It has been concluded, variations in the insulation installation heavy effect the apparent thermal conductivity and are not solely dependent on layer density.
Acknowledgements: We would like to thank our collaborators Wesley Johnson at NASA and Jessica Wood and Susan Bowden at Yetispace. This research is funded by Yetispace, grant# 227000-524-037894. This work was preformed at the National High Magnetic Field Laboratory, which is supported by NSF DMR-1157490 and the State of Florida.
Due to the variety of requirements across aerospace platforms, and one off projects, the repeatability of cryogenic multilayer insulation has never been fully established. The objective of this test program is to provide a more basic understanding of the thermal performance repeatability of MLI systems that are applicable to large scale tanks. There are several different types of repeatability that can be accounted for: these include repeatability between multiple identical blankets, repeatability of installation of the same blanket, and repeatability of a test apparatus. The focus of the work in this report is on the first two types of repeatability. Statistically, repeatability can mean many different things. In simplest form, it refers to the range of performance that a population exhibits and the average of the population. However, as more and more identical components are made (i.e. the population of concern grows), the simple range morphs into a standard deviation from an average performance. Initial repeatability testing on MLI blankets has been completed at Florida State University. Repeatability of five GRC provided coupons with 25 layers was shown to be +/- 8.4% whereas repeatability of repeatedly installing a single coupon was shown to be +/- 8.0%. A second group of 10 coupons have been fabricated by Yetispace and tested by Florida State University, through the first 4 tests, the repeatability has been shown to be +/- 16%. Based on detailed statistical analysis, the data has been shown to be statistically significant.
The main penetrations (supports and piping) through multilayer insulation systems for cryogenic tanks have been previously addressed by heat flow measurements. Smaller penetrations due to fasteners and attachments are now experimentally investigated. The use of small pins or plastic garment tag fasteners to ease the handling and construction of multilayer insulation (MLI) blankets goes back many years. While it has long been understood that penetrations and other discontinuities degrade the performance of the MLI blanket, quantification of this degradation has generally been lumped into gross performance multipliers (often called degradation factors or scale factors). Small penetrations contribute both solid conduction and radiation heat transfer paths through the blanket. The conduction is down the stem of the structural element itself while the radiation is through the hole formed during installation of the pin or fastener. Analytical models were developed in conjunction with MLI perforation theory and Fourier’s Law. Results of the analytical models are compared to experimental testing performed on a 10 layer MLI blanket with approximately 50 small plastic pins penetrating the test specimen. The pins were installed at ~76-mm spacing inches in both directions to minimize the compounding of thermal effects due to localized compression or lateral heat transfer. The testing was performed using a liquid nitrogen boil-off calorimeter (Cryostat-100) with the standard boundary temperatures of 293 K and 78 K. Results show that the added radiation through the holes is much more significant than the conduction down the fastener. The results are shown to be in agreement with radiation theory for perforated films.
Thermal conductivity of low-density materials in thermal insulation systems varies dramatically with the environment: cold vacuum pressure, residual gas composition, and boundary temperatures. Using a reference material of aerogel composite blanket (reinforcement fibers surrounded by silica aerogel), an experimental basis for the physical heat transmission model of aerogel composites and other low-density, porous materials is suggested. Cryogenic-vacuum testing between the boundary temperatures of 78 K and 293 K is performed using a one meter cylindrical, absolute heat flow calorimeter with a aerogel blanket specimen exposed to different gas environments of nitrogen, helium, argon, or CO2. Cold vacuum pressures include the full range from 1x10-5 torr to 760 torr. The soft vacuum region, from about 0.1 torr to 10 torr, is complex and difficult to model because all modes of heat transfer – solid conduction, radiation, gas conduction, and convection – are significant contributors to the total heat flow. Therefore, the soft vacuum tests are emphasized for both heat transfer analysis and practical thermal data. Results for the aerogel composite blanket are analyzed and compared to data for its component materials. With the new thermal conductivity data, future applications of aerogel-based insulation systems are also surveyed. These include Mars exploration and surface systems in the 5 torr CO2 environment, field joints for vacuum-jacketed cryogenic piping systems, common bulkhead panels for cryogenic tanks on space launch vehicles, and liquid hydrogen cryofuel systems with helium purged conduits or enclosures.
The heat transfer between room temperature and 80 K is controlled using various insulating material combinations. The modes of heat transfer are well established to be conduction and thermal radiation when in a vacuum. Multi-Layer Insulation (MLI) in a vacuum has long been the best approach. Typically this is applied to the cold surface. This paper investigates the application of MLI to both the cold and warm surface to see whether there is a significant difference. In addition if MLI is on the warm surface, the cold side of the MLI may be below the critical temperature of some high temperature superconducting (HTS) materials. It has been proposed that HTS materials can serve to block thermal radiation. An experiment is conducted to measure this effect. Boil-off calorimetry is the main method of measuring the heat transfer.
Paris agreement was adopted by consensus on 12th December 2015, then went into effect on 4th November 2016. The necessity to reduce the emission of greenhouse gas is growing on a world scale. We have to consider the substitute energy source of fossil fuel. One of the prospective solutions is hydrogen. In Japan, the concept “CO2 Free Hydrogen Chain” is promoted. The concept is that massive hydrogen produced by electrolysis using renewable energy, or gasification of abundant unused energy such as brown coal (generated CO2 is captured and stored) in foreign country is liquefied to transport effectively, imported into Japan by liquefied hydrogen cargo carrier. In this concept, the technology of storage and transportation of massive liquefied hydrogen is essential. Based on the concept of large tank for liquefied hydrogen, we measured outgas rate from various materials which constitute the vacuum jacket, such as tank, thermal insulation, and support structure. We studied the mechanism of reaction from the data of the outgassing rate for each material, diffusion controlled reaction or the reaction limited at the surface of the material. We treated the material by baking or coating at the surface to reduce the outgas rate, and confirmed the effect comparing with that of untreated materials. We made an analysis of the component of the outgas from the materials and discussed the effect for vacuum degree during the storage of liquefied hydrogen.
Proton Improvement Plant – II (PIP-II) has been planned at Fermilab for providing high-intensity proton beams to the laboratory’s experiments. Fermilab has undertaken the PIP-II Injector Test (PIP2IT) for integrated systems testing of critical components comprising the PIP-II front end. PIP2IT includes two cryomodules, to be tested using an existing Superfluid helium cryogenic refrigerator (SHCP) and distribution box (DB). The PIP2IT transferline connects the DB to the cryomodules of PI2IT. Such cryogenic transferlines are generally provided with cylindrical thermal shields at 80K, enclosing multiple process lines. The thermal shields are cooled by dedicated cooling lines welded/brazed to the shield at a single point along the circumference. Higher thermal diffusivity provides faster cooling and uniformity of temperature along the shield surface. Hence, Copper/Aluminium is widely used to fabricate thermal shields. The fabrication cost depends on the raw material price and the availability of standard size pipes/tubes. To reduce the fabrication cost by making use of easily available stock of standard pipe/tube, it is decided to use stainless steel as a material in thermal shields for the PIP2IT transferline. To this effect, a parametric study has been undertaken to evaluate the suitability of replacing Copper/Aluminium with stainless steel in thermal shields. The low thermal conductivity of steel results in bowing of the shield due to differential temperature distribution along the circumferential direction.
SM18 is CERN main facility for testing superconducting accelerator magnets and superconducting RF cavities. Its cryogenic infrastructure will have to be significantly upgraded in the coming years, starting in 2019, to meet the testing requirements for the LHC High Luminosity project and for the R&D program for superconducting magnets and RF equipment until 2023 and beyond. This article presents the assessment of the cryogenic needs based on the foreseen test program and on past testing experience. The current configuration of the cryogenic infrastructure is presented and several possible upgrade scenarios are discussed. The chosen upgrade configuration is then described and the characteristics of the main newly required cryogenic equipment, in particular a new 35 g/s helium liquefier, are presented. The upgrade implementation strategy and plan to meet the required schedule are then described.
There are five cryogenic plants at Jefferson Lab which support the LINAC, experiment hall end-stations and test facility. The majority of JLab’s helium inventory, which is around 10 tons, is allocated in the LINAC cryo-modules, with the majority of the balance of helium distributed at the cryogenic plant level mainly as stored gas and liquid for stable operation. Due to the organic evolution of the five plants and independent actions within the experiment halls, the traditional inventory management strategy suffers from rapid identification of potential leaks. This can easily result in losses many times higher than the normally accepted (average) loss rate. A real-time program to quickly identify potential excessive leakage was developed and tested. This program was written in MATLAB© for portability, easy diagnostics and modification. It interfaces with directly with EPICS to access the cryogenic system state, and with and NIST REFPROP© for real fluid properties. This program was validated against the actual helium offloaded into the system. The present paper outlines the details of the inventory monitoring program, its validation and a sample of the achieved results.
The MØLLER experiment at Jefferson Lab (JLab) is a high power (5 kW) LH2 target scheduled to be operational in the 12 GeV era. At present, cryogenic loads and targets at three of JLab’s four experimental halls are supported by the End Station Refrigerator (ESR) - a CTI/Helix 1.5 kW 4.5 K refrigerator. It is not capable of supporting the high power target load and a capacity upgrade of the ESR cryogenic system is essential. The ASST-A helium refrigeration system is a 4 kW 4.5 K refrigerator. It was designed to be used as the cryogenic system for the Superconducting Super Collider (SSC) main ring and later obtained by JLab after the cancellation of that project. The ASST-A refrigeration system along with a support flow from JLab’s Central Helium Liquefier (CHL) is considered as an option for the ESR capacity upgrade. The applicability of this system under varying load conditions is investigated. The present paper outlines the findings and the planned approach for upgrading the ESR.
At Niowave, Inc., superconducting electron accelerators are being built to tackle America's high-tech challenges in fields as diverse as health care and national security. To operate these accelerators, we have collaborated with Linde Cryogenics to develop the refrigeration infrastructure required. Niowave operates two standard model compact, mobile, standalone cryogenic systems. The larger system provides 114W of continuous cooling, while the smaller unit provides 5W of cooling. These systems bridge the gap between single run, dewar fed testing, and large scale, facility wide cryogenic systems.
Niowave is also working with Linde to develop an intermediate, 51W, system that would decrease input power and cooling water requirements by half from the 114W system. This refrigeration system will be paired with a pulsed, high-power linac, and would be able to scan cargo containers for nuclear materials. Working with the Domestic Nuclear Detection Office, these systems will protect American borders from potential nuclear threats.
With this array of refrigerator systems in development and operation, Niowave is able to operate its accelerators to develop new technologies for lab and commercial use. These technologies include active interrogation, sterilization, free electron lasers, and radioisotope production.
This contribution will explain the market and applications of these integrated accelerator systems with helium refrigeration. It will also describe the development of intermediate power, systems currently in development, and the on-site installation and operation of these systems.
CERN operates and maintains the world largest cryogenic infrastructure ranging from ageing but well maintained installations feeding detectors, test facilities and general services, to the state-of-the-art cryogenic system serving the flagship LHC machine complex. A study was conducted and a methodology proposed to outsource to industry the operation and maintenance of the whole cryogenic infrastructure. The cryogenic installations coupled to non LHC-detectors, test facilities and general services infrastructure have been fully outsourced for operation and maintenance on the basis of performance obligations. The contractor is responsible for the operational performance of the installations based on a yearly operation schedule provided by CERN. The maintenance of the cryogenic system serving the LHC machine and its detectors has been outsourced on the basis of tasks oriented obligations, monitored by key performance indicators. CERN operation team, with the support of the contractor operation team, remains responsible for the operational strategy and performances. We report the analysis, strategy, definition of the requirements and technical specifications as well as the achieved technical and economic performances after 1 year of operation.
Supercritical helium loops at 4.2 K are the baseline cooling of tokamaks superconducting magnets (JT-60SA, ITER, DEMO, etc.). This loops work with cryogenic circulators that force a supercritical helium flow through the superconducting magnets in order that the temperature stay below the working range all along their length. This paper shows that a supercritical helium loop associated with a saturated liquid helium bath can satisfy temperature constraints in different ways (playing on bath temperature and supercritical flow), but that only one is optimal from an energy point of view (every Watt consumed at 4.2K consumes at least 220W of electrical power). To find the optimal operational conditions, an algorithm capable of minimizing an objective (energy consumption at 5bar, 5K) subject to constraints has been written. This algorithm works with a supercritical loop model realized with the Simcryogenics [1] library. This article describes the model used and the results of constrained optimization. It will be possible to see that the changes in operating point on the temperature of the magnet (e.g. in case of a change in the plasma configuration) involves large changes on the cryodistribution optimal operating point. Recommendations will be made to ensure that the energetic consumption is keeping as low as possible despite the changing operation point. This work is partially supported by EUROfusion Consortium through the Euratom Research and Training Program 2014–2018 under Grant 633053.
[1] : François Bonne, Mazen Alamir, Christine Hoa, Patrick Bonnay, Michel Bon-Mardion, and Lionel Monteiro. A simulink library of cryogenic components to automatically generate control schemes for large cryorefrigerators. IOP Conference Series: Materials Science and Engineering
The large-scale liquid argon Short Baseline Neutrino Far-Detector located at Fermilab is designed to detect neutrinos allowing research in the field of neutrino oscillations. It will be filled with liquid argon and operate at almost ambient pressure. Consequently, its operation temperature is determined at about 87 K. The detector will be surrounded by a thermal shield, which is actively cooled with boiling nitrogen at a pressure of about 2.8 bar absolute, the respective saturation pressure of nitrogen. Due to the strict temperature gradient constraints, it is important to study the pressure drop of the nitrogen two-phase flow along the cooling circuit of the thermal shield in different orientations of the flow in respect to gravity.
An experimental setup has been built in order to determine the pressure drop in nitrogen two-phase flow in horizontal, vertical upward and vertical downward direction. The measurements have been conducted under quasi-adiabatic conditions and at a saturation pressure of 2.8 bar absolute. The mass velocity has been varied in the range of 20 kg/m^2s to 70 kg/m^2s and pressure drop data has been recorded scanning the two-phase region from flow qualities close to zero up to 0.7. The experimental data will be compared with several established predictions of pressure drop e.g. Müller-Steinhagen and Heck by using the void fraction correlation of Rouhani. Implications to existing operational conditions of two-phase flow nitrogen installations at CERN in vertical orientation are presented.
Two-phase heat and mass transfer in nitrogen has been experimentally investigated in a natural circulation loop. The experiments were realized in steady-state conditions near atmospheric pressure with a 10 mm inner diameter vertical copper tube, uniformly heated over roughly 1 m in length. The vapor and total mass flow rates and the wall temperature were measured as a function of the tube heat flux density. The investigated ranges-limits are 40 g/s, 25% and 30 kW/m2 for the total mass flow rate, the vapor quality and the heat flux density respectively. Transition from single phase natural convection to nucleate boiling flow is evidenced by wall temperature measurements at ?different locations along the heated tube. The measurements are compared to the numerical computations of the total mass flow rate that is simulated by a set of conservation equations based on a separated flow model. The model catches most of the features of the mass flow rate evolution as a function of the heat flux density. In addition, the wall temperature measurements are used to determined the heat transfer coefficients that are compared with known correlations in both single phase natural convection and boiling flow. The vast majority of the data falls within ?30% of the predicted values given by the correlations.
In the cryogenic wind tunnel, cooling the circulating gas to cryogenic temperature by spraying liquid nitrogen (LN2) is an efficient way to increase the Reynolds number. The evaporation and motion of LN2 droplets in the high-speed gas flow is the critical process that determines the cooling rate, cooling capacity and the safe operation of the down-stream compressor. In this study, a numerical model of droplet motion and evaporation in high-speed gas flow was developed and verified against experimental data. The droplet evaporation rate, diameter and velocity are obtained during the evaporation process under different gas temperatures and flow velocities. The results show that the gas temperature has dominant influence on the droplet evaporation rate. High flow speed can facilitate droplet evaporation effectively at the beginning process. Evaporation of droplets with different diameters follow similar trend. The absolute evaporation rate increases with the increase of droplet diameter while the relative evaporation amount is highest for the smallest droplet due to its high area-volume ration. This numerical study provides insight for understanding the evaporation of LN2 droplets in high-speed gas flow and useful guidelines for the design of LN2 spray cooling.
Increasing the Reynolds number capability of large wind tunnels is of great importance for the aerodynamic tests, especially in high-speed wind tunnels. Among various methods to increase Reynolds number in transonic wind tunnels, cooling the gas to cryogenic temperature is the optimal solution. In cryogenic wind tunnels, spraying liquid nitrogen has the advantages of rapid and high cooling capacity, low cooling temperature, uniform temperature field, and simple system design. In this study, a CFD model is developed to simulate the liquid nitrogen spray cooling. The model is based on the Lagrangian description of the spray droplets and Eulerian description of the continuum phase, and the droplet evaporation, droplet break up and droplet collision are taken into account. Parametric study is performed to investigate the effects of flow conditions on the evaporation of LN2 droplets and cooling the gas. The comparison between parallel spray and vertical spray is presented for cooling air flow. The results show that high speed of the gas flow can accelerate the droplet evaporation to achieve lower downstream temperature. But the cross-sectional distribution of the temperature becomes less uniform. In vertical spray design, the droplet evaporation as well as the cooling of the gas are much better than that in the parallel spray design due to the high relative velocity between the LN2 droplets and continuous phase.
Jikai Zhu, Xiaobin Zhang
Institute of Refrigeration and Cryogenics, Zhejiang University; The Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province, Hangzhou, 310027, China
Unsteady cavitation characteristics of liquid nitrogen flow through a transparent venturi tube are experimentally and numerically investigated in a variable pressure ratio tunnel. As the pressure ratio (Prat) increases from 1.6 to 2.04, the cavity changes from quasi steady mode to periodic shedding mode. The pressure amplitude exponentially increases as the pressure ratio increases. When Prat exceeds 2.4, a condensation front is visualized within the cavity traveling from the trail to the leading edge. A method using the detected temperature depression in the cavitation is developed to predict the wallis speed of sound within the cavity. It’s found that the visual propagation speed of condensation front agrees well with the corresponding wallis speed of sound. This suggests that the condensation front is the shock wave front. The numerical simulation further confirmed the existence of shock wave generated by the collapse of cavitation cloud which later condenses the attached cavity. The results indicate that shock wave dominates the unsteady shedding process at high Prat but is weak at low Prat. Under the domination of shock wave, shedding frequency in liquid nitrogen cavitation may become higher than that of room temperature fluid without thermal effects because of the bigger propagation speed of sound in cavitation.
The dynamic cavitation characteristics of liquid nitrogen flow over a three dimensional hydrofoil are experimentally investigated in a variable pressure ratio tunnel. The temperature and pressure in the cavity as well as the flow rate are synchronously measured, together with the visual observation of the cavitation unsteady behaviors using the high-speed camera. Cavitation evolutions in a period are captured at different ratio of inlet to outlet pressure. The analyses on measured dynamic pressure data and images reveal that the shedding frequency and length of cavitation cloud linearly increases while the pressure amplitude exponentially increases as the pressure ratio increases. The time-averaged temperature distributions along the hydrofoil surface are presented and analyzed at different pressure ratio. The initial cavitation development and characteristics are also investigated.
The cavitating flow within liquid nitrogen spray nozzles has a profound impact on the spray atomization characteristics and its cooling performance. The CFD simulation is effective for showing the details of complicated and cavitating flow driven by high injection pressure together with small dimensions of the nozzle. The widely used cavitation models including Schnerr and Sauer, Zwart-Gerber-Belamri, Singhal et al., Merkle et al. and Kunz et al. are studied for simulating the cavitating flow within nozzles. In order to obtain a proper model that can reflect cavitating nature in liquid nitrogen spray nozzles, these five cavitation models are analyzed and computed by CFD simulations based on mixture model for both pressure swirl nozzle and simple convergent nozzle. The numerical experiments are carried out under a series of injection pressure, and the vapor volume fraction distributions, outlet vapor quality, mass flow rates and discharge coefficients are obtained. The predicted mass flow rate of each model is compared with the experimental data, which indicates that Zwart-Gerber-Belamri shows best agreement because it properly incorporate the influence of thermal effects. It is also found that Singhal et al. model, Merkle et al. model and Kunz et al. model are less stable while Schnerr and Sauer model is more suitable for room-temperature fluid.
Abstract: Slush nitrogen has lower temperature, higher density and higher heat capacity than those of liquid nitrogen at normal boiling point, and is considered a potential coolant for high-temperature superconducting cables with decreased nitrogen consumption and storage cost. The corrugated pipe can help to compensate the thermal stress generated at low temperature through axial shrinkage. In the present study, a 3-D Euler-Euler two-fluid model has been developed to study the flow and heat transfer characteristics of slush nitrogen in a horizontal corrugated pipe. In this model, the evolution of particle size distribution due to particle breakage is accounted by the population balance equations, and the particle shape and size are taken into considerations by adopting the empirical formula for the effective viscosity of mixture. The numerical model is verified to be effective to predict the slush nitrogen flow by the results compared with empirical formulas. The effects of structural parameters of flow pipes, including pipe diameter, wave length and height of the corrugated pipe, on slush nitrogen flow are then calculated and discussed. Moreover, extensive cases at various working conditions (inlet solid fraction of 5-35%, inlet velocity of 1-5 m/s, heat flux of 0-30 kW/m2) are analyzed, focusing on the pressure drops and heat transfer coefficients of slush nitrogen.
Keywords: slush nitrogen, multiphase flow, pressure drop, heat transfer
Acknowledgement: This work is financially supported by the Zhejiang Provincial Natural Sciences Foundation (LZ14E060001).
Critical current density over 20 MA/cm^2 has been achieved at 30 K, 3 T (B||c) in RE-Ba-Cu-O (REBCO, RE=rare earth) coated conductors made by metal organic chemical vapor deposition (MOCVD) with addition of Zr at levels as high as 25 mol.%. Flux pinning force over 1.7 TNm^-3 has also been achieved at 4.2 K. We have observed a strong dependence of the critical current performance and the (Ba+Zr)/Cu content in the films and in turn, the c-axis lattice parameter. Continuous growth of highly-aligned BaZrO3 (BZO) nanocolumns has been tuned by the difference in lattice parameters of REBCO and BZO. Using a better control of the growth process using Advanced MOCVD, even superior pinning and critical currents have been achieved and extended to thick films as well. The latest advances in the improvement of pinning of heavily-doped REBCO coated conductors will be discussed in this presentation.
The addition of many types of defects to YBa2Cu3O7-z (Y-Ba-Cu-O or YBCO) superconductor thin films have been studied by many groups world-wide, to enhance flux pinning and strongly increase critical current densities (Jcs). Since the first publications of this field in 2003 and 2004, over 6,200 citations have been listed for the subfield ‘flux pinning YBCO’, and the subfield ‘flux pinning’ has over 60,000 citations (source Google Scholar, 2015). Despite many excellent systems studied, there are still interesting types of defect additions, flux pinning mechanisms, and processing methodologies to explore. This paper will provide an introduction to this field, and focus on flux pinning to enhance Jcs at T ≤ 30K and high-fields H ≥ 3 Tesla. Additional emphasis will summarize studies in our lab from 2003 to 2016 on multiple YBCO+M+N systems (M,N < 20 Vol%), where systematic studies characterized the full Jc(T,B,θ) landscape with T = 5-77K, and H = 0–9T, and θ = 0-90º. It is increasing understood that optimized pinning microstructures are typically different for 5K than for 77K, and many examples of that will be shown. However we also will present an interesting YBCO+Y2BaCuO5 system that optimizes pinning for the full range T = 5-77K.
Along with the progress of coated conductors, research to introduce artificial pinning centers into REBCO superconducting films is actively underway. Nanorods and nanoparticles or their hybrid structures were tried as artificial pinning centers, and, as a result, large global pinning forces of 20-30 GN/m3 at 77 K and values exceeding 1TN/m3 at 4.2 K have been realized. However, it is still insufficient to construct a practical model to understand these excellent superconducting characteristics. We consider data from several experiments taken at various conditions in order to discern the nature of the pinning mechanism in REBCO films with artificial pinning centers. Firstly, in this research, we proposed a new model on the angular dependence of Jc caused by nanorods and tried to understand its behavior. In addition, we further improved a flux pinning simulation based on TDGL equation so that it can be applied to REBCO thin film, and attempted to evaluate the optimum pinning volume fraction under the conditions of different temperatures and magnetic fields. According to these results, it became clear that not only the nanorods but also the pinning force of the matrix are very important for controlling the angle dependence of Jc. It is considered that Jc can be improved by adding second pinning centers instead of nanorods alone, as in the hybrid pinning structure. According to the TDGL simulation, the optimum pinning volume fraction is expected to be about 15-20%, but in experimental results it is only 3-5%. We will also discuss this difference.
An introduction of artificial pinning centers (APC) is one of the key techniques to improve a large anisotropy in critical current density $J_c$ REBa$_2$Cu$_3$O$_y$ (RE123, RE: Y and rare earth) tapes. The APC technique is utilized in the practical RE123 coated conductors, recently. One of the most promising APCs is a BaMO$_3$ (M; Zr, Sn, Hf, etc) nanorod, which is a nano-scaled columnar-shaped precipitate. However, the effect of nanorod strongly depends on its size and alignment. In the case of the well-aligned nanorod, which is an ideal case as a c-axis correlated pinning center, the matching field limits the $F_p$ behavior and thus the $F_p/F_p^{max}$ curves are scaled against magnetic field below the matching field but are enhanced in high fields above the matching field with decreasing temperature. This can be explained by the cooperation of the random and correlated pinning model. On the other hand, in the case of the inclined nanorod, the scaling behavior of $F_p-B$ curves below the matching field disappears, and the random pinning contribution appears depending on the nanorod’s alignment. On the other hand, the conventional $F_p$ scaling behavior in $F_p/F_p^{max}$ vs $B/B_{max}$ is observed in the Sm123 tapes without APCs. If we compared the angular dependence of $J_c$ between Sm123 tapes with and without APCs, the enhancement of $J_c$ due to the APC for $B$//c can be seen even at 4.2 K and high fields up to 25 T although the no c-axis peak in angular dependence of $J_c$. Based on the angular and field dependences of $J_c$ in wide temperatures and high magnetic fields up to 27 T, we discuss the correlated and random pinning effects in the Sm123 tapes with and without nanorods.
Acknowledgments: A part of this work was supported by JST-ALCA.
Device fabrication is a key challenge in developing more complex superconducting detectors and cryogenic electronics. In order to explore new detector and circuit ideas, a high degree of flexibility in the fabrication process can permit new devices and design opportunities. However, this flexibility must be balanced by maintaining process stability in order to achieve high yield and develop a deeper understanding of the detailed interactions between design and the fabrication process. Two examples are highlighted, starting with a very simple, single superconducting material layer process for fabricating superconducting nanowire single photon detectors. This simple process is contrasted with a significantly more complex process for superconducting electronics involving nine planarized superconducting material layers, including a high-kinetic-inductance layer, and a resistive material layer. In addition to contrasting the fabrication process approaches used in both cases, some of the successful device and circuit demonstrations will be highlighted and opportunities for future developments will be described.
This work is supported by the Assistant Secretary of Defense for Research and Engineering and the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), via Air Force Contract FA872105C0002. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ODNI, IARPA, or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon.
Superconducting Stripline Detectors (SSLD), which are recently emerging type of detectors, can operate in kinetic inductance detector (KID) mode or transition edge sensor (TES) mode depending on the working conditions. As known, one of the fundamental bottlenecks in the superconducting detector based systems is the integration level which is basically the number of pixels in a detector matrix. DC current biased SSLDs combined with the single flux quantum (SFQ) logic read-out circuits have the potential to reach the integration levels of semiconductor based detectors. This is possible by the monolithic integration of detectors with the read-out circuits, requirement of just one DC bias point for all the SSLD pixels, and relatively simple principle of operation. The utilized principle design is compatible with standard SFQ foundry processes and integrates the detector and addressing circuits in one chip. Thus, it is possible to implement many pixels that would be impossible to achieve otherwise. In addition, the cost of the detector chip is reduced drastically compared to a full custom design and fabrication. In this work we will explain the principle of operation of an SSLD array together with read-out electronics, proposed design and present the experimental results obtained so far.
Acknowledgment: This work was supported by TUBITAK under grant 114E099.
Superconducting nanowire single-photon detectors (SSPDs) with the system detection efficiencies (SDEs) over 80%, which are implemented in compact Gifford-McMahon (GM) cryocooler, are realized and used in a wide range of areas, such as quantum information, quantum optics, optical space communication, fluorescence microscope, and so on. However, in many applications, not only high SDE but also total performance including low dark count rate (DCR), high maximum count rate (MCR) and/or low timing jitter are important to determine the system performance. A multi-pixel SSPD is a promising approach because it enables higher MCR, larger detection area without reducing the MCR, pseudo photon-number resolution and also spatial resolution. We have developed multi-pixel SSPDs combined with cryogenic signal processors based on single-flux-quantum (SFQ) circuits. By employing cryogenic signal processing using SFQ circuit, the number of readout cables and resulting heat load to a cryocooler via the readout cables can be reduced [1]. And also the SFQ circuits can provide a wide variety of functions as post signal processors for multi-pixel SSPDs. In this talk, we will review our recent progress in multi-pixel SSPDs combined with cryogenic signal processors based on SFQ circuit technology.
This work was partly supported by JSPS KAKENHI Grant No. 26249054. The SFQ circuits were fabricated in the clean room for analog-digital superconductivity (CRAVITY) in National Institute of Advanced Industrial Science and Technology (AIST).
[1] H. Terai et al, IEEE TAS 19, 350 (2009).
Superconductor mixed-signal integrated circuits (ICs) offer a compelling solution to the needs of cryogenic detectors. Digitizing detector outputs at low temperature, close to the detectors, ensures naturally noise-immune digital transport to room temperature. This is especially important as the number of detectors increase since analog signal transport is susceptible to crosstalk and noise pick-up. Superconductor integrated circuits, comprising digitizers and digital processors, feature low power conversion, high clock frequency for sampling and digital logic, high sensitivity, and radiation hardness. We describe design and measurement results of several types of readout circuitry: (a) sensitive and fast digitizers for superconducting nanowire single photon detectors (SNSPDs) followed by digital circuitry for optical communication, and (b) time-division multiplexer for detector arrays. We also describe future trends of scaling speed and complexity of superconductor digital circuitry that could enable systems with larger arrays of cryogenic detectors.
Superconducting electronics and spectral-spatial holography have the potential to revolutionize digital communications, but must operate at cryogenic temperatures, near 4 K. Liquid helium is undesirable for military missions due to logistics and scarcity, and commercial low temperature cryocoolers are unable to meet size, weight, power and environmental requirements for many missions. To address this need, Creare is developing a reverse turbo-Brayton cryocooler that provides refrigeration at 4.2 K and rejects heat at 77 K to an upper-stage cryocooler or through boil-off of liquid nitrogen. The cooling system is predicted to reduce size, weight, and input power by at least an order of magnitude as compared to the current state-of-the-art 4.2 K cryocooler, and for systems utilizing nitrogen boil off, the boil-off rate is reasonable, permitting long-duration missions. This paper will review the design of the cryocooler, the key components and component test results.
PIXIE is a recently proposed middle-class explorer mission designed to produce full-sky maps of polarization in the Cosmic Microwave Background (CMB). PIXIE’s challenging science goals require not only measuring the extremely faint “b-modes” of the CMB, but distinguishing between true CMB signatures and 1) polarized light reflecting off local dust, and 2) signals arising from within the instrument. PIXIE’s detectors will operate at 100 mK in order to achieve the required sensitivity. Instrument errors will be minimized in part by operating the telescope and optics at an average temperature close to that of the CMB (2.72 K) and systematically varying the temperature of various components by a small amount (10-20 mK). Signals appearing at the frequency of those variations can then be subtracted out. For this to be successful at the level required, it is necessary for the pattern of temperatures to be stable over very long time frames. Consequently, cooling of the detectors and telescope will be done using two 3-stage ADR assemblies that will produce continuous cooling, one at 100 mK and the other at approximately 2.65 K. The latter will act as the heat sink for 100 mK ADR and establish a base temperature from which the telescope and optics will be regulated. Its heat sink is a 4.5 K cryocooler. The design and operation of the ADRs will be discussed.
Future astronomical instruments will require sub-Kelvin detector temperatures to obtain high sensitivity. In many cases large arrays of detectors will be used, and the associated cooling systems will need performance surpassing the limits of present technologies. NASA is developing a compact cooling system that will lift heat continuously at temperatures below 50 mK and reject it at over 10 K. Based on Adiabatic Demagnetization Refrigerators (ADRs), it will have high thermodynamic efficiency and vibration-free operation with no moving parts. It will provide more than 10 times the current flight ADR cooling power at 50 mK and will also continuously cool a 4 K stage for instruments and optics. In addition, it will include an advanced magnetic shield resulting in external field variations below 5 µT. We describe the cooling system here and report on the progress in its development.
The four 1,280 bolometer detector arrays that will fly on the balloon borne PIPER mission will be cooled by a 4-stage adiabatic demagnetization refrigerator (ADR). Two of the three mechanically independent ADR assemblies provide thermal isolation to their salt pills through Kevlar suspensions while the other provides thermal isolation to its salt pill through the use of bellows and Vespel material. The ADR integrates with the detector arrays and it sits in a large bucket Dewar containing super fluid liquid helium. This paper will describe the complex thermal and mechanical design of the PIPER ADR, and summarize the mechanical analysis done to validate the design.
We present the current state of development in passive gas-gap heat switches. This type of switch does not require a separate heater to initiate heat transfer but, instead, relies upon the warming of one end due to an intrinsic step in a thermodynamic cycle to raise a getter above a threshold temperature. Above this temperature sequestered gas is released to couple both sides of the switch. This enhances the thermodynamic efficiency of the system and reduces the complexity of the control system. Various gas mixtures and getter configurations will be presented.
Several next generation space telescopes (Athena, SPICA, …) requires 50 mK cooling to achieve the desired sensitivity. Such low temperature in space is achieved by using cooling chain coupling different coolers for each temperature range. For the lowest temperature stage, several cooling solutions exists including the use of multi stage adiabatic demagnetization refrigerator (ADR). This paper describes the conception and the first thermal validation of our 3 stage ADR. Two key points for such technologies are the optimization of the heat switches and the choice of paramagnetic material which will be discussed in this paper. As a validation, the classical paramagnet GGG (Gadolinium Gallium Garnett) and CPA (chromic potassium alum) are used as refrigerant. Alternative material choices are presented and discussed.
The Sanford Underground Research Facility (SURF) will host 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. In the current configuration four cryostats will contain a modular detector and a total of 68,400 ton of ultrapure liquid argon, with a level of impurities lower than 100 parts per trillion of oxygen equivalent contamination. The Long-Baseline Neutrino Facility (LBNF) provides the conventional facilities and the cryogenic infrastructure to support DUNE. This contribution presents the modes of operations, layout and main features of the LBNF cryogenic system.
The system is comprised of three sub-systems: External/Infrastructure (or LN2), Proximity (or LAr) and Internal cryogenics. The External/Infrastructure Cryogenics provides the infrastructure and equipment to store, produce and distribute the cryogenic fluids needed for the operation of the Proximity Cryogenics, which delivers them to the Internal at the pressure, temperature, mass flow rate, quality and purity required by the detector inside the cryostat. The External/Infrastructure cryogenics includes the LN2 refrigeration system and the surface facilities, with the receiving stations, the LN2 and LAr storage tanks and the vaporizers. The Proximity Cryogenics includes the LAr and GAr purification systems, the phase separators, the condensers and the piping connecting the various parts. The Internal Cryogenics consists of all the cryogenic equipment located inside the cryostat, namely, the GAr and LAr distribution systems and the systems to cool down the cryostats and the detectors.
An international engineering team will design, manufacture, commission, and qualify the LBNF cryogenic system. The expected performance, the functional requirements and the status of the design are presented in this contribution.
The Super Cryogenic Dark Matter Search (SuperCDMS) experiment is a direct detection dark matter experiment intended for deployment to the SNOLAB underground facility in Ontario, Canada. With a payload of up to 194 kilograms of germanium crystal detectors operating below 15 mK, the cryogenic architecture of the experiment is complex. Further, the requirement that the cryostat presents a low radioactive background to the detectors limits the materials and techniques available for construction, and heavily influences the design of the cryogenics system. The resulting thermal architecture is a closed cycle (no liquid cryogen) system, with stages at 50 and 5 K cooled with gas and fluid circulation systems and stages at 1 K, 250 mK and 15 mK cooled by the lower temperature stages of a large, cryogen-free dilution refrigerator.
This paper describes the thermal design of the experiment, including details of the cooling systems, mechanical designs and expected performance of the system under operational conditions.
Driven by the rising demand for clean energy and the commercialization of fuel cell vehicles, the interest in hydrogen mobility has recently grown. The liquid hydrogen (LH2) supply chain is regarded as a cost effective solution for hydrogen distribution. To meet the demand from a potential hydrogen mobility market, large-scale hydrogen liquefaction plants may soon be required to reach specific liquefaction costs close to 1 € per kg LH2. To this end, two new liquefaction processes developed within this work were modelled and optimized for specific energy consumption and specific liquefaction costs. The optimization results for a range of process configurations and plant capacities between 25 and 100 metric tons per day (tpd) LH2 were presented in a prior publication. The aim of this paper is to present a final cost-optimized 100 tpd LH2 hydrogen liquefier design. To improve the final model predictions for costs and efficiency, the selected process concept is elaborated to a technically ready design which can be implemented within the next 5 years. This step involves accurate heat exchanger calculations with ortho- to para-hydrogen conversion as well as the design of equipment with cost and performance data validated with manufacturers. The herein finally calculated specific liquefaction costs for the 100 tpd LH2 liquefier are reduced by about 67% compared to a conventional 5 tpd LH2 plant. This is achieved with a specific energy consumption close to or below 6 kWh per kg LH2, about 40% lower than for the 5 tpd LH2 plant. The results make a supply chain with LH2 a promising way to reach the future cost targets for hydrogen mobility.
The Short-Baseline Neutrino (SBN) physics program at Fermilab and Neutrino Platform (NP) at CERN are parts of the international Neutrino Program leading to the development of Long-Baseline Neutrino Facility/Deep Underground Neutrino Experiment (LBNF/DUNE) science project. The SBN program consists of three LAr-TPC detectors positioned along the Booster Neutrino Beam (BNB) at Fermilab. The first of these, the MicroBooNE collaboration detector (170 ton LAr mass) was constructed 2011-2014 and operating since 2015. The SBN’s Near Detector (SBND or NP03, ~ 260 ton) is presently under construction. The SBN’s Far Detector (SBN-FD or NP01, ~ 600 tons) is the ICARUS collaboration T600 LAr-TPC, previously operated in Europe and being shipped to Fermilab in 2017. All three LAr-TPC detectors have distinctly different design of their LAr cryostats thus defining specific requirements for the cryogenic systems. CERN and Fermilab are collaborating on the design of the SBN cryogenics while dividing delivery responsibilities for proximity, external and internal subsystems of each detector. CERN is responsible for delivery of the proximity subsystems for all detectors while Fermilab is responsible for delivery of external subsystems, internal subsystem for SBND and integration of subsystems via common safety and controls for all detectors. This contribution presents specific design requirements and typical implementation solutions for each subsystem of the SBND and SBN-FD cryogenic systems.
The waste heat of air compressor in cryogenic air separation unit is typically removed by circulating cooling water. If there is no cooling process, the outlet air temperature can reach as high as 130oC. Traditionally, this part of energy can not be used effectively. Moreover, in the process of multistage compression, the characters of air at the inlet of the compressor are high temperature and high humidity, which result in an increase in the number and the load of compressors.
We proposed a scheme to establish and simulate a coupling system model of the cascade utilization of the waste heat in compression and dehumidification and cooling of the inlet air: the high-grade waste heat of the compressor drives the mixed salt solution to regenerate, then the solution absorbs the moisture in the inlet air of the first-stage compressor and washes the air. The low-grade waste heat of the compressor drives the coupling system of organic Rankine cycle and the vapor compression refrigeration (ORC-VCR), to precool the air at the inlet of the compressors.
This scheme not only makes the waste heat of the compressors be effectively utilized, but also dehumidifies the air with the mixed salt solution, to reduce the load of the compressors and avoid compressing liquid in the air separation process. And through ORC-VCR system, the compressor inlet air temperature is reduced, saving the energy of cooling water to precool the air at the inlet of compressors, and causing the probability of reducing the number of air compressors.
Since the first commissioning in 2005, the cryogenic system for EAST tokamak has been cooled down and warmed up for twelve physical experiments. In order to promote the refrigeration efficiencies and reliability, the EAST cryogenic system was upgraded gradually with new helium screw compressors and new dynamic gas bearing helium turbine expanders with eddy current brake to improve the original poor mechanical and operational performance from 2012 to 2015. Then the totally upgraded cryogenic system was put into operation in the eleventh cool-down experiment, and has been operated for the latest two experimental campaigns. The upgraded EAST cryogenic system has successfully coped with various normal operational modes during cool-down and 4.5 K steady-state operation under pulsed heat load from the tokamak as well as the abnormal fault modes including turbines protection stop and superconducting magnets fast discharge. In this paper, the upgraded EAST cryogenic system including its functional analysis and new cryogenic control networks will be presented in detail. Also, its operational present status in the latest cool-down experiments will be presented and the system reliability will be analyzed, which shows a high reliability and low fault rate after upgrade. In the end, some future necessary work to meet the higher reliability requirement for future uninterrupted long-term experimental operation will also be proposed.
The High Intensity and Energy ISOLDE (HIE-ISOLDE) upgrade project at CERN includes the deployment of new superconducting accelerating structures operated at 4.5 K (ultimately of six cryo-modules) installed in series, and the refurbishing of the helium cryo-plant previously used to cool the ALEPH magnet during the operation of the LEP accelerator from 1989 to 2000. The helium refrigerator is connected to a new cryogenic distribution line, supplying a 2000-liter storage dewar and six interconnecting valve boxes, one for each cryo-module. After a first operation period with one cryo-module during six months in 2015, a second cryo-module has been installed and operated during 2016. The operation of the cryo-plant with these two cryo-modules has required significant consolidations and tunings for the compressor, the cold box and the cryogenic distribution system in order to reach nominal and stable operational conditions. The present paper describes the commissioning results and the lessons learnt during the operation campaign of 2016 together with the preliminary experience acquired during the 2017 operation phase with a third cryo-module.
Cryogenic mixed refrigerant cycles (CMRCs) offer a cost- and energy-efficient cooling method for the temperature range between 60 and 200 K. The performance of CMRCs is strongly influenced by entropy production in the main heat exchanger. High efficiencies thus require small temperature gradients among the fluid streams, as well as limited pressure drop and axial conduction. As temperature gradients scale with heat flux, large heat transfer areas are necessary. This is best achieved with micro-structured heat exchangers, where high volumetric heat transfer areas can be realized.
The reliable design of CMRC heat exchangers is challenging, since two-phase heat transfer and pressure drop in both fluid streams have to be considered simultaneously. Furthermore, only few data on the convective boiling/condensation kinetics of zeotropic mixtures is available in literature.
This contribution presents the design process of a micro-structured heat exchanger with a newly developed numerical model. The governing equations and the solution strategy are briefly outlined, followed by the final design and first experimental results.
Zeotropic mixtures never have the same liquid and vapor composition in the liquid-vapor equilibrium. Also, the bubble and the dew point are separated; this gap is called glide temperature (Tglide). Those characteristics have made these mixtures suitable for cryogenics Joule-Thomson (JT) refrigeration cycles. Zeotropic mixtures as working fluid in JT cycles improve their performance in an order of magnitude. Optimization of JT cycles have earned substantial importance for cryogenics applications (e.g, gas liquefaction, cryosurgery probes, cooling of infrared sensors, cryopreservation, and biomedical samples). Heat exchangers design on those cycles is a critical point; consequently, heat transfer coefficient and pressure drop of two-phase zeotropic mixtures are relevant. In this work, it will be applied a complete methodology in order to calculate the local convective heat transfer coefficients based on the law of the wall approach for turbulent flows. The flow and heat transfer characteristics of zeotropic mixtures in a heated horizontal tube are investigated numerically. The pressure drop, temperature profile, and heat transfer coefficient for zeotropic mixtures of different bulk compositions are analyzed. The numerical model has been developed and locally applied in a fully developed, constant temperature wall, and two-phase annular flow in a duct. Numerical results have been obtained using this model taking into account continuity, momentum, and energy equations. Local heat transfer coefficient results are compared with available experimental data published by Nellis et al. (2005) and Barraza et al. (2016), and they have shown good agreement.
As a more efficient and environment-friendly refrigerant alternative, hydrocarbons have good environmental characteristics and high thermodynamic performances. They have been used as refrigerant in refrigerator and air-conditioning system. The mechanisms of the pressure drop are intimately linked with the prevailing two phase flow regime. Therefore, it is necessary to carried out a universal pressure drop model based on flow patterns for hydrocarbons.
In this paper, a database containing methane, ethane, propane, R600a and other hydrocarbons experimental data points of pressure drop in horizontal tubes was compared with thirteen well-known correlations using the flow regime boundaries proposed by Zhuang et al. (2016). It can be seen that the majority of the correlations predict the annular flow results better than the non-annular flow results. A new pressure drop model based on flow patterns was carried out and predicted well for hydrocarbons.
This work proceeds a numerical study of inclination effect on the heat transfer performance of a tubular heat exchanger. This equipment is widely used in the gasification process of a floating liquefied natural gas system (FLNG) to exploit cold energy from boiled-off liquefied natural gas (BOG). The inclination comes from the FLNG floating in an ocean environment. The finite volume computational fluid dynamics method and the k-ω based shear stress transport model are applied to simulate the heat transfer between BOG and refrigerant. As known from the previous study, the major inclination effect is associated with the inclination in long-axis plane. Therefore, this work focuses on the longitudinal inclination with different angle and mass flow conditions. The simulation result was verified by comparing with the engineering specification data from its supplier - Salof Refrigeration Company in New Braunfels, Texas. The numerical analysis reveals that, in a high mass flow condition (2448kg/h) of shell-side ethylene glycol, the shell-side outlet temperature is relatively more stable than lower mass flow situation. The entire variation range is only 1.3K from inclination -30° to 30°, but 21.3 K in lower mass flow situation. Hence, maintaining higher mass flow of shell-side is an effective way to reduce the inclination effect on shell temperature shift. In addition, outlet temperature of tube side BOG also changes with the inclination angle. There are two approximately linear relations with different variation range between inclination angle and outlet temperature of BOG. The temperature range is 2.9K in higher shell-side mass flow but 6.9 K in lower mass flow. So higher mass flow condition is recommended to achieve a smaller inclination effect on tubular heat exchanger and the outlet temperature of BOG can be predicted by the fitting function of inclination angle.
The efficient re-gasification of cryogen is a crucial process in many cryogenic installations. It is especially important in the case of LNG evaporators used in stationary and mobile applications (e.g. marine and land transport). Other gases, like nitrogen or argon, are used as protective atmospheres, and can be obtained at highest purity after re-gasification in their liquid states. This situation creates a need for high efficiency heat exchangers that are suitable for liquid gas vaporization.
In the present work, the suitability of plate heat exchangers (PHE) for either cryogen vaporization or gas condensation was numerically investigated. A two-phase flow mathematical model was chosen, which included the vaporisation and condensation mechanisms, implemented in OpenFOAM. Based on the real three-dimensional (3D) geometry of an existing PHE, a simplified but consistent two-dimensional (2D) numerical model of the PHE was developed. A series of numerical calculations were performed and when possible, compared with experimental measurements. A 3D numerical model to investigate the flow characteristics in-between the plates of the PHE in a function of the plate design was developed. Particularly, an angle in-between the channels of the PHE (chaveron shape) was studied.
The presented work has been undertaken in the framework of the Poland – Taiwan scientific cooperation, as a part of the project “Development of plate heat exchangers for liquid inert gas vaporization, and the modelling of the two-phase flow in heat exchangers” (PHEVAP), financed by The National Center for Research and Development, Poland, No. PL-WTIII/7/2016.
Counter-flow plate-fin heat exchangers are commonly utilized in cryogenic applications due to their high effectiveness and compact size. For helium liquefaction/refrigeration systems, conventional design theory is no longer applicable and cryogenic heat exchangers are usually sensitive to longitudinal heat conduction, heat in-leak from surrounding and variable fluid properties. Governing equations based on distributed parameter method are developed to evaluate performance deterioration caused by these effects. The model synthetically considering these loss mechanisms is validated against experimental data and design results obtained by commercial software Aspen MUSETM. Multi-channel and multi-stream heat exchangers are further studied to discuss quantitative effect of these heat losses. The numerical method is useful in the design procedure of cryogenic heat exchangers and can be used to predict heat transfer and pressure drop performance under the actual low-temperature environment.
The high voltage (HV) insulation on the ITER magnet feeder superconducting busbars and current leads will be prepared from R-glass fabric, pre-impregnated with an epoxy resin, which is interleaved with polyimide film and wrapped onto the components and cured during feeder manufacture. The insulation architecture consists of 7 half-lapped layers of glass/Kapton, which is then enveloped in a ground-screen, and two further half-lapped layers of glass pre-preg for mechanical protection. The integrity of the HV insulation is critical in order to inhibit electrical arcs within the feeders. The insulation over the entire length of the HV components (bus bar, current leads and joints) must provide a level of voltage isolation of 30 kV.
After installation, the insulated bus bars will be supported by a series of sliding supports (steel clamps) and during machine cool-down the approximately 30m long bus bars will slide within these clamps by up to 30mm; the machine design is for 100 cool-downs.
During operation of the ITER device, there will be large (up to 15kN per clamp) Lorentz forces on the bus bars that are reacted through the clamps. Many of the ITER magnets are pulsed and during machine operation the bus bars will slide up to 5mm during each of the 30,000 lifetime pulses.
This worked was aimed at assessing the wear on, and the changes in, the electrical properties of the insulation when cycled through ±5mm for twice the ITER lifetime cycles at a constant load of 15kN. A total of 4 specimens were tested, and the average radial wear (underneath the clamps) after 60’000 cycles was 0.75 mm. This is less than the radial build of the pre-preg layers which cover the ground-screen. High voltage tests demonstrated that the electrical isolation of the insulation was intact after the fretting test.
Disclaimer
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
Recent studies on prototype undulator magnets showed that second-generation high temperature superconducting (2G-HTS) tapes are suitable for use in undulators to enhance their performances substantially. However, providing sufficient mechanical stability and rigidity to the magnet windings have remained a challenge. Vacuum epoxy impregnation is a widely employed technique to improve the mechanical properties of magnet windings. So far, most of the impregnated 2G-HTS coils/magnets showed some degree of degradation after the first cold cycle or subsequent cold cycles. In this study, we developed a vacuum impregnation technique that does not degrade the performance of the 2G-HTS undulator prototype magnets even after repeated cold cycles. The results showed that in order to prevent degradation, either the epoxy thickness around the coil stack needs to be kept small or a bumper layer between the magnet winding stacks and the epoxy needs to be introduced. Microstructure images of vacuum impregnated coil packs showed uniformly spaced 2G-HTS winding layers and very thin epoxy fillings between the layers, which is important for the overall performance of the device.
Composite materials, due to their high strength to weight ratio, are deployed in various aerospace applications such as skins of the empennages (aircraft), launch vehicle bodies, support structures in spacecraft, etc. However, the cryogenic tanks for storing super cooled fuels such as liquid nitrogen (LN2), liquid oxygen (LOX), liquid hydrogen (LH2), etc. in spacecraft are still constructed by means of metals. Even with years of testing, still the concern exists about the leakage of tanks at cryogenic temperatures due to the microcracking of composite laminates such as carbon/epoxy. These microcracks arise owing to difference in the coefficients of thermal expansion in axial as well as transverse directions. The composites exposed to very low temperatures (cryogenic temperatures) causes thermo-mechanical loading even at moderate pressure, due to which the crack propagates that leads to the formation of leakage paths. These leakage paths allow the fuels to leak that cause the ignition and explosion hazard. However, in order to overcome such catastrophic incidences, Kevlar®, a Para-aramid synthetic fibre, proves a promising alternative to be used for cryogenic storage tanks. Kevlar® composite had proved to be a highly suitable material for applications ranging from sports equipment and body armour to spacecraft. In the present work, the failure behaviour of Kevlar®/Epoxy laminate (60% fibre volume fraction) under uniaxial tensile load ranging from 100MPa to 1000MPa is determined by using the extended finite element method (XFEM) approach. A three-dimensional Kevlar®/Epoxy laminate of 50x30x1mm with a 5mm edge crack at the mid position of the laminate is considered for analysis. Further,stress-strain characteristics of Kevlar composite are compared with those of normal metals (SS316LN) used for cryogenic storage tank applications.
The special test facility consisted of 15.5 T superconducting magnet and a variable temperature insert (VTI) has been installed in the radiation control area at Oarai center in Tohoku University in Japan. The VTI has a high purity aluminum rod with over 6 nine to remove the heat from a sample holder to GM refrigeration. Also, it has a pair of pure copper bus bars of 500 A. Since these materials are mechanically week and low stiffness, it was found that the heat transferring ability had been changed after the sample current tests when they were carried out under 15 T. The main reason was considered to the electro-magnetic force acted on the fixed point of the high purity aluminum rod which looked like a cantilever. The connection part of the aluminum rod and a main copper plate which was cooled down by two sets of GM refrigerator was re-polished and strengthened by attaching additional supports. After the reconstruction, the sample tests were succeeded and new data on the neutron irradiated Nb3Sn wire was obtained. The Nb3Sn wires were irradiated by fission neutron in JRR-3, a fission reactor, and by 14 MeV pure neutron in Fusion Neutron Source. It was found that the 14 MeV pure neutron irradiation caused a larger change in the critical current than that by fission neutron and it showed there is a clear effect of neutron energy spectrum on the critical current.
One major inhibitor to a hydrogen society is economical systems to support safe storage and transportation of this fuel. Magnetic refrigeration has emerged as a promising technology for hydrogen liquefaction due to its potential high efficiency and environmentally friendly operation. Magnetic refrigeration utilizes the magnetocaloric effect (MCE), which is the temperature variation of a magnetic material after exposure to a magnetic field. Several critical challenges exist for developing low cost magnetic refrigerators. Challenges specific to MCE materials include the cost, availability, stability, and performance of the material in a refrigeration device (i.e. where fast magnetization and demagnetization cycles are required). The best known MCE materials for sub 80K applications are expensive rare-earth. We are developing low cost rare-earth Ce- and Nd- based ternary alloys which yield only 2nd order phase transitions (no hysteresis) and performance (DS) higher than current best materials. With small changes in the composition, the MCE response temperature can be shifted between 10K-50K, allowing system based optimization for various liquefaction applications. Work is ongoing to optimize processing, performance, and shaping of the MCE materials into a useable structure for magnetic refrigeration devices.
Wire drawing is a tremendously expanding industry which incorporates manufacturing of steel wires having applications in automotive, construction, agriculture, and equipment manufacturing industries. The wire drawing die is usually manufactured from tungsten carbide and cobalt binder, commercially called as cemented carbide.The tungsten carbide die plays a vital role in shaping wires. In this research, we made an effort to improve service life of carbide die from material strengthening perspective. Worn out samples of tungsten carbide dies were collected from reputed wire industry and analysed under FE-SEM to understand their wear behaviour. The as received samples were tested for microstructural analysis under FE-SEM and X-ray diffraction analysis. Wear test and microhardness test was also carried out. Samples were then treated with normalising treatment followed by cryogenic treatment. The cryogenically treated samples were given tempering for 5, 10 and 15 hours and were analysed using the same characterisation tools. Phase analysis showed appreciable decrease in Cobalt binder content of cryotreated specimen tempered for 15 hour, which also showed increase in hardness by 7.6%. Pin-on-disc wear test carried out for cryotreated and tempered specimens simulating the speeds used in wire drawing. Wear test showed an appreciable decrease in wear rate. The dissolution of binder cobalt and stress induced precipitation of carbides is predicted to be the reason behind enhancement of mechanical and tribological properties of the material. Thus, cryogenic treatment with subsequent tempering is a promising heat treatment process to improve wear behaviour and thus the service life of wire drawing dies.
Keywords: Tungsten carbide dies, cryogenic treatment, tempering, wear behaviour
Acknowledgements: Authors would like to acknowledge BEKAERT India for the provision of carbide dies and Physics Department of Smt. Savitribai Phule Pune University for X-Ray Diffraction analysis.
Sumitomo Electric Industries, Ltd. (SEI) has been developing the silver-sheathed Bi2223 multi-filamentary wires, DI-BSCCO (Dynamically-Innovative BSCCO). The wires have been improved various properties in response to the growing demands from the application products and projects. For use in high field-magnet applications, strong hoop stress is usually applied to HTS wire. Therefore, the wire needs to have high mechanical strength. For the purpose of using such applications, SEI has developed and commercialized a high-strength DI-BSCCO Type HT-NX wire reinforced with Ni alloy tapes. The wire obtained a critical tensile stress of 400 MPa at 77K. On the other hand, the resistivity of the Ni alloy is high, resulting in the generation of the high Joule heat at the joint. The newly developed spliced structure successfully reduced the splice resistance without sacrificing the mechanical properties. For nuclear magnetic resonance and other high field magnetic applications, the use of Type HT-NX wire is highly expected. In this presentation, the recent progress of the currently available commercial wires and the updated R&D activities will be talked.
Due to steady progress in both performance and application engineering, Bi-2212 round wires are increasingly attractive materials for ultra-high field (>25 T) magnets. In recent work to further improve the critical current density and repeatability of long length performance, we have worked closely with several US powder suppliers and national laboratories on Bi-2212 powder development. These efforts include optimizing powder stoichiometry and phase composition, and focusing the creation of economical and reproducible processes. Through our broad collaborations, we have also made efforts to make it easier to use Bi-2212 wires in high stress coils. We have looked at both reinforcing the wire by adding strong materials, and reinforcing coils by co-winding with strong materials. To meet practical application requirements, the wire piece length has been significantly increased by improving our processing conditions and enlarging our production billet size. A 0.8mm wire of piece-length over 2400m has been achieved and today wire lengths of 1 km are routine. We have also improved insert coil performance by optimizing the wire size and filament configurations and using densification techniques. The latest results of Bi-2212 wire development and properties will be presented in detail.
JC and JE in Bi-2212 round wire is high enough for high-field magnet applications and it is now available in km-long piece lengths. Recent studies of Bi-2212 conductor are geared towards advancing the understanding and technology needed for Bi-2212 to be successful in high-field magnet applications. These include studies directed at understanding Bi-2212 overpressure processing heat treatment (OPHT) to make the heat treatment more robust, at increasing and characterizing the strength of Bi-2212 strand with high-strength metal strips laminated on slightly-aspected wire to control strain in coils, and at developing insulation materials for wind-and-react coils. The talk will highlight these advances in Bi-2212 conductors.
A Bi2212-based, high temperature superconductor has been developed in reinforced, rectangular wire forms, with up to 400 MPa stress tolerances and high current densities, making them suitable for use in transposed cables, coils and magnets that are problematic with wide HTS tapes, and that need to operate beyond the field and temperature limits of low temperature superconductors. Our program has recently established long length production capability for a rectangular form of this wire, that we are now applying to develop robust, transposed, HTS-wire based cables and compact, high-field coils employing a wind-and-react approach that is similar to what is used with Nb3Sn. We have designed, produced and tested wires with varied reinforcement levels in straight and coiled forms, with the results validating that usefully high critical current densities (Je’s) and strengthening are achieved with low cost materials, scalable processes, and a simple final reaction step. Based on these data, we have now designed a strong, Bi2212-based wire for boosting field from ~ 22T to ~ 30T as required in, for example, a 1.2 GHz NMR system, while enabling the coil to fit into the available volume, and providing it with the required stress tolerance, insulation, operating current and current density at 4K. We have produced test lengths of this wire into a variety of small-scale solenoidal coils with the objective of establishing the wire-related techniques required to build an NMR insert type of coil, including insulation, strengthening with non-magnetic reinforcement, layer winding with smooth layer transitions, as well as connection of current leads.
Bi-2212 round wire is currently being developed for high-field magnet applications. The large critical current densities of present state-of-the-art Bi-2212 strands, coupled with their relatively ductile Ag/Ag alloy matrix, leads to stress-limited performance in many high field solenoids. The critical current degrades as a function of stress due to the onset of progressive fracture of the Bi-2212 filaments. For this reason, strand reinforcement is highly desirable to increase the stress limits at higher fields. Reinforcement can be achieved in a variety of ways, however, the application of a high-strength metallic alloy bonded to the long flat faces of rectangular strands of Bi-2212 (produced by Solid Material Solutions) show promising preliminary results in doubling the stress limits of 2212 strands (from 150 MPa to 300 MPa). Research in the application of these techniques to produce a strengthened HTS strand and their characterization for high field coil technologies is ongoing. Here we report on the challenges and results when reinforcing Bi-2212 for high field applications.
Key words: Bi-2212, high field magnet, conductor development, stress, strain, coil technology
Acknowledgement: This work was performed at the National High Magnetic Field Laboratory, supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida and also supported by the US Department of Energy Office of High Energy Physics under grant 227011-520-032288 and the National Institute of Health under grant R21GM111302.
Minimizing hysteresis losses and maximizing transport critical current density (J$_{ct}$) of superconducting wires is important for all magnet applications. In multi-filamentary Bi-2212 round wires, filaments can couple physically by grain-to-grain contacts (bridging) developed during heat treatment, providing either a strong, fully coupled or a weak SNS coupling. Bridging is especially prevalent in architectures with densely packed filaments and the associated loss component persists at high fields, unlike proximity coupling. Bi-2212 is the only high J$_c$ round wire HTS conductor, allowing it to be twisted, similar to LTS wires. Twisting helps reduce losses by constraining coupling currents to flow only across lengths of half the twist pitch instead of the entire length of the conductor but it may also be that twisting reduces bridging losses through the same mechanism. However, twisting has also been speculated to reduce J$_{ct}$ by damaging filaments, and by eliminating pathways around current-blocking obstacles that filament-to-filament coupling may provide. We are investigating the effect of twisting on hysteretic losses and J$_{ct}$ of overpressure (OP) processed Bi-2212 round-wires with both densely packed (37x18, heavy bridging) and sparsely packed (27x7, virtually no bridging) filament architectures. We used transport J$_c$ and magnetization hysteresis measurements to quantify changes in hysteretic losses and J$_{ct}$. We observed that twisting reduced hysteretic losses by 67% for the unbridged 27x7 and by 26% for the strongly bridged 37x18 wires while having no effect on J$_{ct}$. Twisting appears to be an effective way of improving the hysteretic loss characteristics of OP Bi-2212 round wires without compromising the crucial transport properties.
This work was supported by the US Department of Energy (DOE) Office of High Energy Physics under grant number DE-SC0010421, by the National High Magnetic Field Laboratory (which is supported by the National Science Foundation under NSF/DMR-1157490), and by the State of Florida.
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Niobium superconducting circuitry requires a 4K environment for the materials to exhibit their enabling quantum mechanical properties. Thus superconducting electronics (SCE) has a highly symbiotic relationship to cryocoolers: SCE technologies cannot transition into the hands of fielded war-fighters without coolers capable of mobile operation and vibration survival. A mass commercial application at 4K requires miniaturization to under a cubic foot and idiot-proof design, an even more challenging standard. Without a guarantee of a solid market, the motivation to commercially fund development of a rugged 4K cooler is much weaker. This talk will focus on 4K, Nb based logic circuits and will illustrate the progress toward system demonstrations made over the past 15 years. These will illustrate the improvements still needed from the cooler and leads communities. Then other cryogenic applications of superconductivity based on thin film technologies and requiring < 20K environments will be reviewed. How those applications stress their coolers in the same or different ways as the Nb logic circuits will be discussed.
The paper systematically reviews developments of novel heat switches at cryogenic temperatures, which can alternatively provide high thermal connection or ideal thermal isolation to the cold mass. These cryogenic heat switches are widely applied in a variety of unique superconducting systems and critical space applications. The discussion and review will include the following technical devices: 1) magnetic levitation suspension post and bearing, 2) shape memory alloys switches, 3) differential thermal expansion thermal switches, 4) helium or hydrogen gap-gap heat switches, 5) superconducting-normal switches, 6) piezoelectric heat switches, 7) cryogenic diode heat switches, and 8) mechanical demountable connections. The comparisons of the advantages and limitations of different cryogenic heat switches are briefly discussed along with the outlook for future thermal management solutions in materials and cryogenic designs.
Additive manufacturing techniques using composites or metals are rapidly gaining momentum in cryogenic applications. Small or large, complex structural components are now no longer limited to mere design studies but may move into the production stream thanks to new machines on the market that allow for light-weight, cost optimized designs with short turnaround times. The potential for cost reduction as compared to bulk materials machined to tight tolerances has become obvious.
Furthermore, additive manufacturing opens doors and design space for cryogenic components to date did not exist or were not possible in the past, using bulk material and associated elaborated and expensive machining processes, e.g. micromachining.
The cryogenic engineer now faces the challenge to design toward those new additive manufacturing capabilities. Re-thinking designs toward cost optimization and fast implementation however also require detailed knowledge of mechanical and thermal properties at cryogenic temperatures.
In the following, we show a possible roadmap for additive manufacturing applications of parts and components typically used in cryogenic engineering designs.
High-temperature ionic salts are central to several promising technologies for green energy and industrial synthesis: concentrated solar power, safe nuclear fission, and high-temperature batteries for smart grid applications.
Several methods used for thermal management in cryogenics have been used to solve critical design challenges that have until now inhibited those technologies.
The methods and their parallels will be presented.
The cryogenic distillation has long been applied in the extensive production of industrial gases because of its features of high efficiency, high purity, and capability to produce noble gases, and it still plays a dominant role at present. Exploring methods to improve the mass transfer efficiency in cryogenic distillation is of great theoretical and practical significance. The negative correlation between the susceptibility of paramagnetic oxygen and temperature provides a new possibility for comprehensive utilization of boiling point and susceptibility differences in the cryogenic distillation. For example, the magnetic force acting on liquid oxygen reached 120.3 N/kg, that is, 12 times the gravity, under 0.5 T magnetic field with the gradient of 100 T/m. Starting from the concept, we proposed a novel distillation intensifying method by using gradient magnetic field, in which the magnetic forces promote the transport of the oxygen molecules to the liquid phase in the distillation. In this research, a cryogenic testbed was designed and fabricated to study the diffusion between oxygen and nitrogen under magnetic field. Mach-Zehnder interferometer was applied to visualize the concentration distribution during the liquid-liquid and vapor-liquid mass transport process. The diffusion characteristics and overall mixing time with and without magnetic field, in the chamber filled with the magnetic medium, were systematic revealed. The concentration redistribution of oxygen was observed, and the overall mixing time in the diffusion between liquid oxygen and nitrogen was prolonged by the nonuniform magnetic field. Moreover, in the mass transfer between vapor oxygen and liquid nitrogen, the magnetic medium promoted the partial condensation of oxygen and affected the characteristics of bubble. The experimental results show that the magnetic field can efficiently influence the mass transfer in cryogenic distillation, and provides a new way for the optimization of air separation process.
Attaining cooling effect by using laser induced anti-Stokes florescence in solids appears to have several advantages over conventional mechanical systems and has been the topic of recent analysis and experimental work. Using anti-Stokes fluorescence phenomenon to remove heat from a glass by pumping it with laser light, stands as a pronouncing physical basis for solid state cooling. Cryocooling by fluorescence is a feasible solution for obtaining compactness and reliability. It has a distinct niche in the family of small capacity cryocoolers and is undergoing a revolutionary advance. In pursuit of developing laser induced anti-Stokes fluorescent cryocooler, it is required to develop numerical tools that support the thermal design and therefore a thorough analysis of combined heat transfer mechanism within the cryocooler is necessary. The paper presents the details of numerical model developed for the cryocooler and the subsequent development of a computer program. The program has been used for the understanding of various heat transfer mechanisms and is being used for thermal design of components for an anti-Stokes fluorescent cryocooler.
The High Luminosity LHC (HL-LHC) is a project aiming to upgrade the LHC collider after 2020-2025 in order to increase the integrated luminosity by about one order of magnitude and extend the physics production until 2035. An upgrade of the focusing triplets insertion system for the Atlas and CMS experiments is foreseen using superconducting magnets operating in a pressurised superfluid helium bath at 1.9 K. This will require the design and construction of four continuous cryostats, each about sixty meters in length and one meter in diameter, for the final beam focusing quadrupoles, corrector magnets and beam separation dipoles. The design is constrained by the dimensions of the existing tunnel and accessibility restrictions imposing the integration of cryogenic piping inside the cryostat, thus resulting in a very compact integration. As the alignment and position stability of the magnets is crucial for the luminosity performance of the machine, the magnet support system must be carefully designed in order to cope with parasitic forces and thermo-mechanical load cycles. In this paper, we present the conceptual design of the cryostat and discuss the approach to address the stringent and often conflicting requirements in terms of alignment, integration and thermal aspects.
At CERN in collaboration with various high energy physics partners, design studies for the proposed Future Circular Collider are underway and cover new electron-positron and proton-proton colliders. A 100 km long circular tunnel is foreseen featuring caverns for four general purpose detectors probing the e-e+ and p-p collisions. The design effort shall lead to a conceptual design report by the end of 2018 for preparing the next step and eventually leading a new collision machine by medio 2045.
Options for the new detector magnets are being explored. The design effort since 2014 has led to baseline designs for both the ee+ and pp detector magnet systems. For the pp detector the 14 GJ magnet system features a 10 m diameter, 19 m long, 4 T central solenoid in combination with two 5 m free bore, 3.5 m long 4 T solenoids covering the low angle forward directions. For the ee+ detector the baseline comprises a more classical 0.74 GJ solenoid providing 2 T in a 6.6 m free bore and 8 m length. The peak magnetic field in the coil windings is 4.6 T and 2.5 T respectively comfortably within reach of NbTi technology.
The design drivers for these magnets set by physics requirements will be highlighted. Various design options for the records breaking magnets are presented as well as an outlook is given on the conductor development and coil engineering needed.
A second-generation cryocooler-based cryostat has been designed and built to support a new helically wound superconducting undulator (SCU) magnet for the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). The design represents an evolution of existing SCU cryostats currently in operation in the APS storage ring. Value engineering and lessons learned have resulted in a smaller, cheaper, and more efficient cryostat design compatible with existing planar magnets as well as the new helically wound device. We describe heat load and quench response analyses, design and operational details, and the “build-to-spec” procurement strategy. The new cryostat also supports the potential for dry (liquid helium-free) operation which could lead to even simpler and more compact designs.
Most of the wiggler and undulator magnets that are used for storage rings and free electron lasers are room temperature permanent magnets. Superconducting wiggler and undulator magnets have been built, but their performance has been limited by the engineering current density of superconductors used to fabricate the coils. Superconducting undulators must have a small gap, which can be a hindrance when the beam vacuum chamber is at room temperature. Beam heating requires that a cryogenic vacuum chamber be cooled to a temperature between 20 and 40 K. Permanent magnets fabricated from Nd-Fe-B can be cooled to cryogenic temperatures with an increase in the magnetic field generated within the undualtor gap. This permits the gap to be reduced considerably with the cooling of the vacuum chamber the same cooling as the magnet cooling. This paper discusses the cryogenic cooling of both superconducting and permanent magnets.
The ITER Central Solenoid Model Coil (CSMC) is a superconducting magnet, layer-wound two-in-hand using Nb3Sn cable-in-conduit conductors (CICCs) with the central channel typical of ITER magnets, operating since ~15 years at the National Institutes for Quantum and Radiological Science and Technology, Naka, Japan. Six conductors (out of the 36 needed for the 18 CSMC layers) are instrumented with differential pressure measurement and flow meters, so that their hydraulic characteristics can be directly measured. Since slightly different CICCs were used for different layers (two different void fractions in the bundle region and, for one of the two, spiral versus coiled wire used for the central channel), three groups of hydraulically similar conductors can be clearly identified on the basis of the conductor geometry.
The aim of this work is to give an overall view of the issues related to the hydraulic performances of the different CICCs used in the CSMC, on the basis of an extensive experimental database put together during the past 15 years. The hydraulic characteristics of the three different types of conductors are deduced from the two latest test campaigns (2015 and 2016, respectively) and compared to those measured during the first one in 2000, as well as to short conductor sample data, when available.
This database is used to derive consistently more general correlations for the CSMC conductors friction factors, based for instance on a porous-medium treatment for the bundle region and in a wider range of Reynolds number with respect to what was done so far. It is also shown that the hydraulic performance of the CSMC conductors did not suffer any permanent change or degradation in the sequence of test campaigns over the last 15 years.
A superconducting segment coil of whole-body-MRI-relevant size was developed and tested for its overall performance, with subsequent testing of induced normal zone formation, quench propagation, and protection. The coil had a 909 mm outer diameter (OD), with a winding cross section of 50 mm (height) by 25 mm (radial). It was wound with 22 layers (29 turns per layer) of multifilamentary MgB2 wire (wire size: 1.19 mm by 1.81 mm) and was epoxy impregnated by VPI. The coil was conduction cooled via copper straps and bolted connections to a Cu ring connected to two Sumitomo cryocooler with 1.5 W each at 4 K. The coil was instrumented with 40 voltage tap pairs and 15 thermocouples, as well as several hall probes and cernox temperature sensors. The coil was tested for overall performance in a conduction cooled mode by measuring critical current (Ic) as a function of T up to 35K. Spot heaters were used to induce quenches in order to study normal zone propagation properties, and to test the effectiveness of an active protection scheme developed for this coil. As part of this protection circuit a coil protection structure was embedded into the MgB2 coil perimeter which was fired upon quench detection. The overall coil performance as well as the performance of the protection circuit were analyzed and are discussed.
Cable-in-conduit has been used to advantage for superconducting windings for tokomaks, NMR spectrometers, and superconducting energy storage for many years. Beginning with the Nuclotron at Dubna and then the SIS100 ring at GSI, a ‘cable-outside-conduit- has been used successfully for accelerator dipoles.
The Accelerator Research Lab has developed a NbTi cable-in-conduit for use in collider magnets, and we are putting it into first service for the 3 T dipoles and quadrupoles for the Ion Ring of the proposed Jefferson Lab Electron-Ion Collider (JLEIC). Superconducting wires are twist-cabled around a perforated center tube, the cable is pulled into a sheath tube, and the sheath is drawn down to compress the wires against the center tube and immobilize.
We have fabricated prototype windings in which small-radius saddle-ends are formed on each turn. We have measured the conductor placement precision in the finished windings, and verified that the systematic and random multipoles in the magnetic field distribution that would be produced meets the dynamic aperture requirements for a hadron collider.
Designs will be presented that include a dual dipole for a 500 TeV Collider-in-the Sea, and a ~16 T dipole in which CIC windings utilize Nb3Sn and Bi-2212 wires.
In this talk we will probe characteristics and failure mechanisms of composite superconductors during a quench, arriving at the conclusion that strain control of composite superconductors is the key to prevent degradation of superconductors within a superconducting magnet during a quench. Experimental data and analysis will be given to support the arguments that for Nb3Sn wire, Bi-2212 wire, MgB2 tape and wire, and Bi-2223 tape, degradation during a quench is driven by axial strain, and that for ReBCO coated conductors, degradation is mostly driven by the tendency of REBCO coated conductor to delaminate, caused by the thin film multilayered structure developing peeling stress when experiencing localized temperature rises. We will explore the implications of these findings on designing superconductors, cables, and magnets, and give predications of practical quench-induced degradation limits of these superconductors. The importance of this work will be illustrated using the case of recently developed Sumitomo CT-OP Bi-2223-NX high strength tapes, for which the practical axial stress limit is experimentally proved to be far less than those determined by the conventional axial stress-strain tensile measurement, and determined under various bending strain, high Lorentz forces, and high current and with presence of a quench.
We have developed a 2 W class 4 K pulse tube cryocooler, Cryomech model PT420, for applications that require large cooling capacities, such as a superconducting magnet and dry dilution, etc. This paper presents the optimization of the prototype PT420 with regard to structure and operating parameters. This prototype has bottom temperatures of 24.7 K for the 1st stage and 2.3 K for the 2nd stage. It can provide 65 W at 45 K on the 1st stage and 2.15 W at 4.2 K on the 2nd stage, with a power input of 10.5 kW. A model PT820 is a modified version from the PT420 for 10-20K applications. The prototype PT820 can provide the cooling capacity of 28 W at 20 K and 130 W at 80 K. These cryocoolers have the highest cooling capacity and efficiency to date, of the two-stage pulse tube cryocoolers.
Fabrum Solutions, in collaboration with Absolut System and Callaghan Innovation, produce a range of large pulse tube cryocoolers based on the metal diaphragm pressure wave generator technology (DPWG). The largest cryocooler consists of three in-line pulse tubes working in parallel on a 1000 cc swept volume DPWG. It has demonstrated 1280 W of refrigeration at 77 K, from 24 kW of input power and was subsequently incorporated into a liquefaction plant to produce liquid nitrogen for an industrial customer.
The pulse tubes on the large cryocooler each produced 450 W of refrigeration at 77 K. However, pulse tubes can produce more refrigeration with higher efficiency at higher temperatures. This paper presents the results from experiments to increase liquefaction throughput by operating one or more pulse tubes at a higher temperature to pre-cool the incoming gas. The experiments showed that the effective cooling increased to 1500 W resulting in an increase in liquefaction rate from 13 to 16 l/hour.
Callaghan Innovation and Fabrum Solutions, in collaboration with Absolut System, have produced a range of large pulse tube cryocoolers. The cryocoolers are based on Callaghan Innovation’s metal diaphragm pressure wave generator technology (DPWG) which has matured over the last 10 years to become a viable option for providing acoustic power to large pulse tube cryocoolers. The largest cryocooler, based on a 1000 cc swept volume DPWG, has demonstrated 1280 W of refrigeration at 77 K, from 24 kW of input power, was incorporated into a liquefaction plant to produce liquid nitrogen for an industrial customer and has been producing liquid nitrogen a rate of 10-11 litres per hour. Experience gained in operating the large cryocooler in an industrial environment for over a year has led to the development of an integrated turn-key gas-separation-to-liquid system mounted on a mobile platform. This paper presents the design and development of the turn-key system and test performance from the integrated liquefier.
The pulse tube cryocooler has the advantage of no moving part at the cold end and offers a high reliability. To further extend its use in commercial applications, efforts are still needed to improve efficiency, reliability and cost effectiveness. This paper generalized several key innovations in our cooler products. The cooler consists of moving magnet compressor, and coaxial cold finger. Ambient displacers were employed to recover expansion work to increase cooling efficiency. In the cold-finger, the conventional flow straightener screens were replaced by a tapered throat between cold-head heat exchanger and pulse tube, in order to strengthen its immunity to the working gas contamination as well as to simplify the manufacturing processes. The Cold-head itself, was made by copper forging process which further reduced the cost. In the compressor, a new gas bearing design has brought in assembly simplicity and running reliability. Besides the cooler itself, electronical controller is also important for actual application. A dual channel and dual driving mode control mechanism were selected, vibration could be reduced to minimal, and cooling rate could be faster, and run-time efficiency could be higher. With these innovations, the cooler TC4189 obtained 44 K no-load temperature and 15W cooling power at 80K, with an input electric power of 244 W, which means an efficiency of 16.9% of Carnot. The whole system has a total mass of 4.3 kg.
This study proposes a multi-stage heat-driven travelling-wave thermoacoustic refrigeration system operating at liquefied natural gas temperature, which consists of two thermoacoustic engines and one thermoacosutic cryocooler in a closed-loop configuration. Three thermoacoustic units connect each other through a resonance tube of small cross-sectional area, achieving “self-matching” for efficient thermoacoustic conversion. Based on the linear thermoacoustic theory, a model of the proposed refrigeration system has been built by using DeltaEC software to show the acoustic field distribution, operating characteristics and performance. It is shown that with charging pressure of 5 MPa and helium as working gas, the thermoacoustic engine part is able to build a stable and strong acoustic field with a frequency about 75 Hz. When hot temperature reaches 923 K, this system can provide over 1 kW cooling power at 110 K with an overall exergy efficiency of 16%. This study indicates a great application prospect of travelling-wave thermoacoustic refrigeration system in the field of natural gas liquefaction and superconducting cooling. A corresponding prototype is under construction and experimental study will be started later this year to compare with the simulation results.
A highly-reliable cryocooler with kw-class cooling capacity is considered as a promising candidate for application in the small-scale liquefied natural gas plant. This paper introduces a three-stage traveling-wave thermoacoustically-driven cryocooler desirable for such demand. By including three thermoacoustic engine units and a pulse tube cooler in a traveling-wave loop with different-diameter resonance tubes, this configuration is characterized by high efficiency and large power gain. Theoretical analysis is performed based on the thermoacoustic program. Firstly, axis distributions of phase difference and acoustic power are presented and analyzed. Then, the flow area ratio between adjacent resonance tubes is studied, which is found to be crucial for the system performance. Experimental investigations are conducted on the global cooling performance, and the current result has shown the feasibility for utilization at liquefied natural gas temperature range. With further improvement, a total exergy efficiency of 8 % is expected to be achieved at 130 K.
The Cryocooler for the Mid Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) provides cooling at 6.2K on the instrument interface. The system design has been incrementally documented in previous publications and has components that traverse three primary thermal regions on JWST: Region 1, approximated by 40K; Region 2, approximated by 100K; and Region 3, which is at the allowable flight temperatures for the spacecraft bus. However there are several sub-Regions that exist in the transition between primary regions and at the heat reject interfaces of the Cooler Compressor Assembly (CCA) and Cooler Control Electronics Assembly (CCEA). The design and performance of the test facility to provide a flight representative thermal environment for acceptance testing and characterization of the complete MIRI cooler subsystem are presented.
Perceiving a need for space-qualified tactical cryocoolers suitable for shorter, higher risk-tolerant missions, Ball established a new approach to cryocooler electronics. An entirely new architecture, rooted in past experience and optimized with today’s technology, was developed that could be scaled to different power needs and could be configured for different missions or coolers as appropriate. To reflect this flexibility, the new architecture is called the Scalable Configurable Cryocooler Electronics (SCCE). The first SCCE iteration drove a Sunpower MT cryocooler to a measured efficiency over 95%. Control of an active balancer for vibration reduction was also demonstrated. The second SCCE iteration drove a Ball SC235E Stirling cryocooler. This iteration demonstrated the same electronics hardware could be used to drive different cryocoolers with only minor software changes. The design has 2 high power drive channels and two low power channels. This allows the same design to be used for two independent tactical coolers or a single larger aerospace Stirling class cooler. Thus, a single hardware solution can drive coolers ranging from 50 W to 400 W or higher with minor changes to parts selection and software. Various operational modes are possible including constant power, constant temperature, or open loop. These can be combined so that the power mode becomes a limit so that a user can select a temperature set point, and the cooler will be controlled from ambient down to cryogenic temperatures without violating the power limit. An engineering model SCCE has been completed and flight unit builds are underway.
This paper describes the thermal performance, exported vibration, and magnetics testing and results of a Lockheed Martin high-power micro pulse tube cryocooler. The thermal performance of the microcooler was measured in vacuum for heat reject temperatures between 200 and 300 K. The cooler was driven with a Chroma 61602 AC power source for input powers ranging from 10 to 60 W and drive frequency between 115 and 140 Hz. The optimal drive frequency was dependent on both input power and heat reject temperature. In addition, the exported forces and torques of the cooler were measured with the cooler driven by Iris LCCE-2 drive electronics for input powers ranging from 10 to 60 W and drive frequency between 135 and 145 Hz. The exported forces were dependent on both input power and drive frequency. Finally, the DC and AC magnetic fields around the cooler were measured at various locations.
This paper presents a review of recent advances in single- and multi-stage Stirling-type pulse tube cryocoolers (SPTCs) for space applications in National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences (NLIP/SITP/CAS).
A variety of single-stage SPTCs covering 25–150 K become mature, in which several mid-sized ones operating in 80–110 K have debuted in space. Impressive progresses are achieved in the ones operating 30–40 K because they employ neither double-inlet nor multi-bypass and use common stainless steel meshes as regenerator matrices. Another important advance is the micro SPTCs with an overall mass of 300–800 g operating at high frequencies varying from 100 Hz to 400 Hz, which have important applications in both space and aeronautics fields.
The main purpose of developing two-stage SPTCs is to simultaneously acquire cooling capacities at both stages, in which normally the second stage works in 30–35 K while the first in 85–150 K. They exclude the external precooling to facilitate applications.
The three-stage SPTCs are developed mainly for applications at around 10 K, which are also used for precooling the J-T coolers to achieve further lower temperatures. Both thermally-coupled and gas-coupled arrangements are studied and the entropy analysis is employed for optimization.
The four-stage SPTCs are developed to directly achieve the liquid helium temperature for cooling space low-Tc superconducting devices and for the deep space exploration as well.
The high performance linear compressor is another key technology of vital importance in developing the enabling space SPTCs. The design, optimization and manufacturing methods of various linear compressors for the single- and multi-stage SPTCs are reviewed, in which the dynamic and thermodynamic characteristics, the scaling approaches and the optimal match are emphasized.
Several typical development programs are described and an overview of the data package is presented.
The development of pulse tube cryocoolers (PTCs) at Shanghai Institute of Technical Physics, Chinese Academy of Sciences (SITP, CAS) is presented. These PTCs can provide cooling power from mW to tens of watts over a range of temperatures from 20 K to 170 K, which can be used to cool varieties of detectors in space applications, such as quantum interference device, radiometer, ocean color sensor and so on, because these detectors have to work at a specific temperature in order to increase signal to noise ratio (SNR), sensitivity and optical resolution. SITP has delivered many of the space-borne cooler systems and has many long life pulse tube and Stirling coolers on orbit. This paper reviews the development of the single-stage PTCs over a range of weights from 1.5kg to 10kg, and presents the results of a two-stage PTC development program.
The technical capabilities of cryogenic sensors and their scope of application continue to grow. In the Quantum Sensors Group at NIST, we are developing both transition-edge sensors (TESs) and microwave kinetic inductance detectors (MKIDs) for a broad range of applications including x-ray materials analysis, nuclear security, terrestrial imaging, and astrophysics. We describe a subset of recent developments including (1) the recent dissemination of cryogenic x-ray spectrometers to both small laboratories and large light source facilities, (2) the successful fabrication and dissemination of MKID arrays containing several thousand pixels for submillimeter astrophysics, and (3) the emergence of powerful microwave readout techniques for both TES and MKID devices. The dissemination of sensors that operate at sub-Kelvin or few-Kelvin temperatures depends on and also motivates the development of suitable cryogenics. While commercial cryogenic technology is often sufficient, NIST has also conducted several recent projects to develop refrigerators optimized for sensors. These projects include the development of two generations of adiabatic demagnetization refrigerators, chip-scale refrigerators based on quantum tunneling, and an ultracompact cryorefrigerator to achieve temperatures slightly below 2 K. The latter unit is based on a custom-designed three-stage pulse tube and a Joule-Thomson cooling loop. We briefly describe these cryorefrigerator projects, particularly the 2 K cooler and its application to the refrigeration of nanowire sensors.
Quantum computing architectures with ten or more quantum bits (qubits) have been implemented using trapped ions and superconducting devices. The next milestone in the quest for a quantum computer is the realization of quantum error correction codes. Such codes will require a very large number of qubits that must be controlled and measured by means of classical electronics. One architectural aspect requiring immediate attention is the realization of a suitable interconnect between the quantum and classical hardware. In this talk, I will introduce the quantum socket, a three-dimensional wiring method for qubits with superior performance as compared to two-dimensional methods based on wire bonding. The quantum socket is based on spring-mounted micro wires – the three-dimensional wires – that connect electrically to a micro-fabricated chip by pushing directly on it. The wires have a coaxial geometry and operate well over a frequency range from DC to 10 GHz. I will present a detailed characterization of the quantum socket and a proof of concept for quantum computing applications, where a quantum socket was used to measure superconducting resonators at a temperature of ~10 mK. I will then discuss another technology for extensibility based on chip-to-chip thermo-compressive bonding. I will present a series of experiments where two chips containing superconducting devices were bonded together. In particular, I will present results for the bonding resistance at 10 mK and experiments where superconducting resonators made from indium were fabricated beneath a protective superconducting tunnel. In conclusion, I will give an outlook demonstrating how the quantum socket ands chip-to-chip bonding can be used to wire a quantum processor with a 10 × 10 qubit lattice and I will outline our present work toward the implementation of such a lattice.
Cryogenic low noise amplifiers (LNAs) find regular use in a wide variety of applications ranging from radio astronomy to quantum computing. When operating at physical temperatures below 20$\,$K, amplifiers based upon InP high electron mobility transistors (HEMTs) and SiGe heterojunction bipolar transistors (HBTs) regularly achieve noise temperatures about an order of magnitude above the quantum limit. These amplifiers have typically been used in relatively simple systems, where the power consumption of the amplifiers was of secondary importance. As such, commercial cryogenic LNAs have not been optimized for power and typically consume 5$\,$mW or more. Future systems that are desired for THz radio astronomy and quantum computing will require that a thousand or more amplifiers be integrated within a single closed-cycle cryostat. As the maximum power that can be removed from a typical 4$\,$K closed-cycle cryocooler is limited to about 1.5$\,$W, the power consumption of the LNAs will be limited to a small fraction of this number.
In this paper, we will review our recent efforts towards minimizing the power consumption of silicon germanium cryogenic low-noise amplifiers. First, a discussion of the relationship between power consumption and performance for both InP HEMTs and SiGe HBTs will be given and it will be shown that SiGe HBTs have the potential to operate at near optimum noise performance with microwatt level power consumption. Next, several proof-of-concept ultra-low-power discrete and integrated circuit LNAs will be presented. Finally, the paper will conclude with a description of a THz heterodyne receiver that leverages this technology to realize a single pixel that operates at DC power consumption of just 300$\,\mu$W.
The iron-based superconductors of K-doped (Ba,K)Fe2As2(Ba-122) are potentially useful for high field applications due to their high upper critical fields of over 50T and small anisotropy. However, improvement of Jc is still required to PIT processed Ba-122 tapes for such applications. Two important factors that much influence Jc of PIT Ba-122 tapes are the density and c-axis grain orientation of Ba-122 core in the tapes. We succeeded in obtaining large improvement of Jc values applying stainless steel(SS)/(Ag-Sn) double sheath materials. The Jc reaches to the practical level of 105A/cm2 in magnetic fields up to 10T for flat rolled SS/(Ag-Sn) double sheathed tapes. These higher Jc values than those for pure Ag sheath and SS/Ag double sheath should be attributed to the more improved density and c-axis grain orientation of Ba-122 core together with the smoother interface between Ba-122 core and the Ag-Sn inner sheath. Recently we fabricated ~1m long Ba-122/SS/(Ag-Sn) double sheath tape. The tape was cut into 20 short tapes and Jc values were measured. Jc scattering along the tape length is fairly small with maximum and minimum Jc values of 7.2x104 and 5.5x104 A/cm2 at 4.2K and 10T, respectively. We also carried out bending tests of the double sheath tapes. We bent the tapes, made them straight and measured Jc values at 4.2K and 10T. Degradation of Jc was observed at the bending diameter of 30mm which corresponds to bending strain of around 0.17% in Ba-122 layer.
Iron pnictide superconductors are very attractive in the application of high magnetic field region, because of their large upper critical field, small anisotropic, etc. However, the practical realization requires pnictide wires having high transport current property, large mechanical property, multi-filamentary, homogeneity in long length, low cost. A lot of works had been carried out to solve the problems associated with these factors. Recently, we have made further improvement in the high-field Jc on 122 type pnictide wires, which exhibited a transport Jc value as high as 5×10^4 A/cm^2 at 26 T, 4.2 K. The high density nano-scale defects formed in the superconducting core possibly account for this large in-field Jc. We have also got new results in the Cu-sheathed pnictide wires. By using a low temperature sintering process, the Cu-sheathed Sr122 samples exhibit a high Jc 3.5×10^4 A/cm^2 in 10 T and 1.6×10^4 A/cm^2 in 26 T at 4.2 K, respectively. This fascinating result indicates a promising future for Cu using as the sheath material in pnictide wires. At the same time, wires with a good mechanical property have been fabricated using Fe/Ag as composite sheath material in Sr122 wires. The composite sheath provides both inert reaction with the superconducting core and high mechanical property of the wires. It is expected that further optimized properties in pnictide wires can be obtained based on improved manufacturing technologies.
The transport performance of 122 superconducting wires depends on impurity level, phase purity, the porosity, as well as the presence of micro-cracks. Here we investigate the formation and properties of BaK-122 precursors prepared using a high-energy ball milling (SPEX Milling) method. In this work we used tungsten-carbide ball-milling media, rather than stainless steel, as contamination from the Fe-based milling media is known to degrade the superconducting properties of the resulting wires. Using this approach, the milling times and reaction processes were re-optimized, and high quality BaK-122 mechanical alloyed precursors were obtained and processed to wires by drawing. Samples of these wires were then densified using both standard rolling as well as our biaxially cold high pressure densification (BCPD) approach. In this approach, pressures up to 1 GPa can be applied along two-axes at the same time, allowing for much higher levels of densification than standard rolling. The BCPD approach led to wires with higher levels of densification than the control samples or the rolled samples. In addition, we observed a much lower level of micro-cracking with the BCPD samples, correlating to its higher transport performance. Optical and SEM analysis are shown to be consistent with density and transport measurements.
Iron-based superconductors (IBSs) have very promising characteristics for high-field applications [1]. Among various IBSs, 122-type compounds are most extensively studied due to their reasonably high $T_c$, $H_{c2}$, and $J_c$. In particular, (Ba,K)Fe$_2$As$_2$ single crystal has a large Jc, and it can be enhanced over 1x10$^7$ A/cm$^2$ (4.2 K, self-field) after irradiation [2,3]. Several techniques have been applied to fabricate superconducting wires and tapes of IBSs. Among them, round wires fabricated using the powder-in-tube (PIT) method is most suitable for winding high-field magnets. Up to now, (Ba,K)Fe$_2$As$_2$ and (Sr,K)Fe$_2$As$_2$ PIT wires have been fabricated, and reasonably high in-field $J_c$ has been reported [4-6]. In this talk, present status of $J_c$ characteristics of PIT round wires of 122-type materials are reviewed. We also report the latest result of the highest $J_c$ of 4.0x10$^4$ A/cm$^2$ at 4.2 K under 10 T in (Ba,K)Fe$_2$As$_2$ PIT wire. Extensive characterizations of the wire including X-ray diffraction, EDX analyses, and magneto-optical imaging will also be reported.
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After the discovery of Fe-based superconductors (FBS), a lot of efforts have been made in the fabrication of high-quality epitaxial FBS thin films. As a result, thin films of three different FBS on technical substrates have been realized, which shows the possibility of FBS coated conductor applications. Recently, the successful deposition of a P-doped BaFe$_2$As$_2$ (Ba-122) film on ion beam assisted deposition MgO template by pulsed laser deposition has been reported [1]. The P-doped Ba-122 coated conductor sample is capable of carrying a critical current density ($J_c$) of 10$^5$ A/cm$^2$ at 15 T for both $H$//$ab$ and $c$, which is superior to MgB$_2$ and Nb-Ti. By analysing the $E$-$J$ curves for determining $J_c$, a non-Ohmic linear differential signature is observed at low magnetic fields due to flux flow along the grain boundaries (GBs), which is the hallmark of grain boundary limitation of $J_c$. However, GBs work as pinning centres at the same time as demonstrated by the pinning force analysis [2].
A portion of this work was performed at the National High Magnetic Field Laboratory, which was supported by National Science Foundation Cooperative Agreement No. DMR-1157490, and the State of Florida. The work at Tokyo Institute of Technology was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Element Strategy Initiative to Form Core Research Center. K.I. acknowledges support by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (B) Grant Number 16H04646. H.Hi was also supported by JSPS for Young Scientists (A) Grant Number 25709058, JSPS Grant-in-Aid for Scientific Research on Innovative Areas Nano Informatics (Grant Number 25106007), and Support for Tokyotech Advanced Research (STAR).
[1] H. Sato et al., Sci. Rep. 6, 36828 (2016).
[2] K. Iida et al., Sci. Rep. 7, 39951 (2017).
High-quality thin films are the fundamental basis for the realization of weak electronics and power applications in iron-based superconductors (IBSs), and the coated conductor is an important topic for superconducting applications. In this study, we investigated the transport properties of FeSe0.5Te0.5 (FST) thin films fabricated on poorly-aligned metal tape substrates (7.72°) with LaMnO3(LMO) as buffer layers using pulsed laser deposition [1]. A self-field transport critical-current density of up to 0.43 MA cm−2 at 4.2 K has been observed in FST thin films, which is much higher than that in powder-in-tube processed FST tapes. The films are capable of carrying current densities of over 10^5 A cm−2 in the whole applied magnetic field up to 9 T, showing great potential for high-field applications. The results suggest that for IBSs highly textured metal tape, which is an absolute necessity in achieving cuprate-coated conductors with high-performance, is not needed to produce high-performance coated conductors.
[1] Zhongtang Xu, Pusheng Yuan, Yanwei Ma and Chuanbing Cai Supercond. Sci. Technol. 30 (2017) 035003