We Shall recall the ongoing and future projects using SRF thin films and list the opening of new synsergies
"Niobium thin film radio-frequency (RF) cavities have historically shown performance degradation as the RF field increases, posing limitations on their use in particle accelerators where the real-estate gradient has to be maximized. This issue, often referred to as the medium field Q-slope problem, has not yet been fully understood and is currently undergoing extensive studies.
We examined...
Within my contribution, I want to focus on the theory of the Dynes superconductors and its implications for the studies of the superconducting cavities. Assuming various regimes of pair-breaking and pair-conserving disorder within our approach leads to rich behavior of the resonant frequency shift close to 𝑇𝑐. I want to elaborate on the following points. A) Present a more finalized discussion...
While Nb3Sn theoretically offers better superconducting RF cavity performance (Q0 and Eacc) to Nb at any given temperature, peak RF magnetic fields consistently fall short of the ∼400 mT prediction. The relatively rough topography of vapor-diffused Nb3Sn is widely conjectured to be one of the factors that limit the attainable performance of Nb3Sn-coated Nb cavities prepared via Sn vapor...
"High-Tc superconductors (HTS) have recently become competitive options in superconducting magnet applications. It is natural to investigate their potential in superconducting RF (SRF) cavities. The most advanced HTS, the copper oxide family, has been successfully developed for low-field cavities for dark matter experiments under strong static magnetic fields. However, their gapless nature may...
"Recent technological advances allow the use of HTS Coated Conductors in RF devices by soldering the tape onto an appropriately shaped substrate. This opens up the possibility of manufacturing entire RF accelerating cavities using this technology. A collaboration between CERN, ICMAB, KIT and SLAC aims at assessing the performance attainable by RF components produced with this technology by...
"Magnetron sputtering (MS) is a common technique used for the production of thin films. In such process, the sputtered ions are ejected from the target material with high kinetic energy and deposited onto the substrate to form the coating. This result in an energy transfer between the bombarding particles and substrate, affecting film growth or crystallization.
While DC and pulse DC are...
Coating the inner surface of superconducting radio frequency (SRF) cavities is one of the approaches to push ultimate limits in next generation accelerators. One of the potential coating techniques for such intricate and large volume structures is atomic layer deposition (ALD), as it offers full and uniform layer coverage. In order to predict the process parameters for coating SRF cavities on...
The SRF cavities made with a niobium coating on a copper substrate (Nb/Cu) offer several advantages over those made with bulk niobium. This is mainly attributed to the excellent thermal properties of copper, enabling operation at higher temperatures and consequently reducing cryogenic costs. The Nb/Cu technology has been employed at CERN since the 1980s, being currently used in the LHC and...
"The Future Circular Collider (FCC), foreseen to be built at CERN, relies on the Nb/Cu technology for the 400 MHz RF system. In view of reaching the requested specifications, it is of uttermost importance to push the SRF performance of the Nb thin films to its limits. To do so, it appears critical to understand what are the underlying physical phenomena that drive the Q-slope. Such an effect...
The Nb/Cu film superconducting cavities offer several enhancements over traditional bulk niobium RF cavities, including improved mechanical and thermal stability, as well as a reduced sensitivity to DC magnetic fields. Despite these advantages, Nb/Cu film cavities produced via DC magnetron sputtering often exhibit a pronounced Q-slope issue, potentially due to the low-energy deposition...
In this study, we addressed the persistent medium-field Q-slope issue in Nb thin film cavities, which, despite their high Q at low RF fields, exhibit a significant Q-slope at medium RF fields compared to bulk Nb cavities. Traditional heat treatments, effective in reducing surface resistance and mitigating the Q-slope in bulk Nb SRF cavities, are challenging for Nb thin film cavities. We...
"As part of efforts to reduce both energy and helium consumption in future particle accelerators, such as the Future Circular Collider (FCC), investigations into alternative methodologies to bulk Nb and Nb/Cu technologies are of paramount importance. Thanks to its higher transition temperature (Tc) and lower BCS surface resistance (RBCS), Nb3Sn coated cavities should produce a quality factor...
"he development of Nb3Sn films on copper as coatings for the accelerating cavities of next generation particle accelerators is mainly driven by the sustainability goals being at the core of the I.FAST project. The successful development of a Nb3Sn/Cu scalable prototype would allow for the operation of the SRF system at 4.5 K, resulting in a reduction of the needed cryogenic power by a factor 3...
Nb3Sn has significant potential for superconducting radio-frequency (SRF) application in future particle accelerators, especially compact accelerators, which have attracted the attention of many scientific researchers. This work reports the setup and process of Nb3Sn coating at the Institute of High Energy Physics (IHEP), and presents the results of 1.3 GHz 1-cell cavities coated with Nb3Sn....
We will present on the evolution of Nb3Sn-coated accelerator cavity performance from the qualification test to the test in CEBAF cryomodule. Two Nb3Sn-coated 5-cell accelerator cavities were first measured at 4 K and 2 K in the vertical dewar test, then assembled into a CEBAF quarter cryomodule. Several precautions were taken and changes were implemented in the assembly procedures to preserve...
Copper-based Nb3Sn cavity is a promising candidate for next generation accelerator applications in the field of superconducting radio frequency (SRF). It combines the excellent thermal conductivity of copper and the superior superconducting properties of Nb3Sn, and has the potential to greatly improve the performance of the SRF cavity. The electrochemical and thermal synthesis (ETS) bronze...
Copper-based Nb3Sn cavity is a promising candidate for next generation accelerator applications in the field of superconducting radio frequency (SRF). It combines the excellent thermal conductivity of copper and the superior superconducting properties of Nb3Sn, and has the potential to greatly improve the performance of the SRF cavity. The electrochemical and thermal synthesis (ETS) bronze...
Nb3Sn has shown much promise in recent years for use in superconducting radio frequency SRF cavities. Applying and reacting a large-area thin film homogenously on the inside of a cavity requires new ingenuity in material science. We present methods to form a range of Cu-Sn composition on Cu substrates using evaporation, and we achieve Cu-Sn phases with high tin activity to facilitate...
"Nb3Sn coatings in accelerating cavities have been proposed as an alternative to drastically reduce the overall cryogenic cost in modern SRF complex accelerators. Furthermore, Nb3Sn films are among the candidates conceived to cover the interior of superconducting cavities for the search of axions (haloscopes). Thus, there is noticeable interest in assessing the superconducting properties of...
In this study we report on PVD deposition of Nb3Sn sputtered directly from an alloy target at elevated temperature about 600 °C with and without of interlayer of thick Nb layer deposited on copper substrate producing a multilayer of Cu/Nb/Nb3Sn and Cu/Nb3Sn.
The dependence of superconducting properties of the total structure on deposition parameters is been determined. The films have been...
With a higher Tc and higher critical field Hc than Nb and many Nb compounds and alloys, MgB2 is anticipated to be a promising material to be used for superconducting RF (SRF) cavities at ~20 K. We report our continuing effort towards MgB2 coated SRF cavities. MgB2 films as thick as 5 um were coated on 1.3 GHz TESLA type Cu RF cavities by hybrid physical-chemical vapor deposition (HPCVD). The...
Bulk Nb superconducting radio-frequency (SRF) cavities are widely used in accelerators, and their accelerating gradient and general performance are limited by the superheating field (Bsh). To push the theoretical limit of the Bsh, new multilayer structures are required. We fabricated Fe(Se,Te)-coated Nb films using pulsed laser deposition, performed structural characterizations, and measured...
This work describes recent developments for Nb3Sn films from sintered and stoichiometric 2-inch niobium tin targets by PVD. The final objective is to develop high quality thick Nb3Sn films (on Nb and on Cu), and SIS multilayers on SRF cavities. The effects of the target power, coating thickness, annealing temperature, and annealing time on the superconducting properties of films (RRR/Tc) were...
"For the last few decades, the material of choice for SRF cavities has been bulk niobium. RF performance of bulk $Nb$ cavity has already approached its theoretical limit. To enhance RF cavity performance and cost-efficiency, research has shifted towards the use of other alternative higher $T_c$ materials, such as $NbN$, $NbTiN$, $MgB_2$, etc. However, the use of alternative superconducting...
We introduced the New DC magnetron sputtering apparatus at KEK to create multi-layer structure on the inner surface of a superconducting radio-frequency cavity. This apparatus has the capability of coating Nb3Sn, NbN, and AlN to the elliptical 3 GHz SRF cavity as well as flat substrates up to 2-inche diameter area. The film formation using the flat sample is useful for searching the ideal...
The general method for manufacturing superconducting accelerating cavities with an elliptical cell shape is to press-form niobium sheets into a bowl shape and join them together using electron beam welding (EBW). Research on manufacturing cavities at a low-cost using hydroforming instead of EBW has been achieved. Another research has been actively conducted in recent years to manufacture the...
One of the most promising avenues of research for next-generation superconducting cavities is to increase the operating temperature ≥ 4.2 K by depositing new thin-film superconducting materials with temperatures at least twice as high as the Niobium currently used. These possibilities pave the way for the development of new cooling techniques (cryocooler with liquid He cooling circuits...
"The performance of superconducting radio frequency (SRF) cavities is critically influenced by surface preparation. Traditionally, electropolishing (EP) has been employed to achieve a clean, low-roughness surface on both niobium (Nb) and copper (Cu) substrates, despite requiring harsh and corrosive acids. Since 2019, our research at LNL has focused on an alternative approach: Plasma...
Niobium EP and BCP progress has the problems of slow polishing rate and high risk of electrolyte. In order to solve this, our team uses a less hazardous and more environmentally-friendly HF-free electrolytes, non-aqueous solvent as electrolyte. High efficiency polishing of niobium can be achieved by applying high pulse voltage. The polishing rate is dozens or even hundreds of times that of...
A liquid helium-free cryostat for RF testing of superconducting cavities has been designed and constructed. G-M cryocoolers are used to provide cooling capacity, with heat leakage less than 0.02 W at 4 K. The vertical test of the Nb3Sn cavity and the horizontal test of the Nb cavity were carried out with the cryostat using different connection structures between the 4 K stage of the cryocooler...
At Daresbury Laboratory, fast RF characterisation of planar thin film coated samples is being performed on a dedicated facility. It is a LHe-free facility using a 7.8 GHz Choke Cavity to test planar samples 90-130 mm in diameter and 2-10 mm thickness. A simple sample mounting procedure, and straightforward measurements of surface resistance using an RF-DC compensation method, allows this...
Copper cavities can be deposited with a thin film of superconducting material in order to test the RF performance of the thin film. Traditional thin film copper cavities are produced from 2 half cells, which are then welded across the equator, however these cavities can suffer from poor coating quality and field enhancement on the weld.
An alternative approach instead involves producing...
At Daresbury Laboratory, two new cryogenic facilities have been designed, built and tested for RF testing of 1.3 GHz thin film coated cavities. The first facility is a high power vertical test stand that has been designed to test both single-cell and multi-cell cavities in LHe at 2 and 4.2 K. The advantage of this facility is that it will be operating in the SuRF lab facility that is already...
Superconducting radiofrequency cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, Eacc, where Eacc is limited by the maximum magnetic field, B, that can be applied on the surface of the accelerating cavity wall. To increase Eacc, the maximum B field, Bmax, which can be applied to the surface, must also be increased. The A15 materials or...
Coating Nb with thin layers of one or more superconductors with longer penetration depths, $\lambda$, has been proposed to achieve accelerating gradients, $E_{\mathrm{acc}}$, beyond Nb's fundamental limit. Such heterostructures can sustain the Meissner state above each layer's superheating field, $B_{\mathrm{sh}}$, due to the strong suppression of the screening currents in the surface layers...
"Positron annihilation spectroscopy (PAS) is a precise probe of point defects in nanomaterials. It enables to sense defect densities in the range of 1015-1019cm-3. Positrons localize in the neutral and negatively charged open volume defects, i.e. vacancies and their agglomerations, extended defects or pores. The time to annihilation of the positron with an electron depends on local electron...
A program of quantitative measurements of the expulsion of magnetic flux from flat macroscopic samples has been used to categorise expulsion efficiency, and to assess the practical expulsion effects of closed-topological cooling on thin film structures. Specifically, the closed-topology cooling has permitted systematic and repeatable measurements of the magnetic response over the...
Stable operation of a cavity generally requires Joule-heating, generated in its walls, to be conducted to an outer helium bath. Therefore, it is of interest to experimentally evaluate how present and future cavity treatments affect thermal characteristics. We present an instrument for measuring the thermal performance of SRF cavity materials at cryogenic temperatures. To get an idea of the...
"Superconducting radio frequency (SRF) resonators are newly being used in the quantum regime (at temperatures below 1 Kelvin) for integration into 3D quantum computing processing units. The motivation behind these new applications lies in the fact that SRF cavities offer a coherence lifetime that is 1000 times longer than other 2D qubit architectures and provide sensitivities that are orders...
Point Contact Tunneling Spectroscopy (PCTS) is a powerful technique ideal for investigating the surface superconducting properties of materials. Since it utilizes the oxides present on the sample’s surface to probe the superconducting density of states, this tool is valuable for studying devices such as qubits and SRF cavities, where a native or engineered oxide layer is present on the...
To achieve higher acceleration gradients, we are investigating alternatives to classical superconducting niobium cavities. New concepts, such as passivating the high-loss native oxide surface or employing multilayer systems, are promising approaches. Atomic layer deposition (ALD) has proven to be a suitable method for coating the inner surface of a cavity homogeneously and with sub-nanometer...
Multipacting in particle accelerator elements such as drift tubes, superconducting radiofrequency resonating cavities (SRF), couplers… is a major challenge. The multipacting phenomenon is strongly dependent on the surface total electron yield (TEEY) and developing thin film coatings materials to reduce the surface TEEY is of critical importance. In most cases however, the surface dissipation...
To enhance heat-transfer efficiency in SRF cavities, we previously introduced a novel approach that coats the cavity with an inner-wall thermal-conducting film (ITCF). Simulation results showed that ITCF absorbs heat from the RF surface and transmits it to cooler neighbouring regions on the inner wall, thereby reducing the heating-point temperature via an extra heat-transfer route. This work...
This study aims to assess the quality of PEALD-based SIS films and involves several steps to show significant correlations between different measurement results. The growth per cycle is determined by XRR, from which the respective thicknesses of the PEALD-coated thin films are derived. The results are used to determine the London penetration depth λL of a thin superconducting NbTiN layer...
RF properties of superconductors (SC) in high magnetic fields have recently become of great interest in view of their applications in large experiments in fundamental physics. Indeed, the quantum sensing of dark matter axions [1] and other elusive signals such as high frequency gravitational waves (GW) [2], or the beam screen for the CERN Future Circular Collider (FCC) [3], can greatly benefit...
The development of simpler, compact Superconducting RF (SRF) systems represents a new research thrust in accelerator science. These compact accelerators rely on advancements made to both Nb3Sn SRF cavities and commercial cryocoolers, which together allow to get rid of the operational requirement for liquid cryogenics. This approach to SRF cavity operation, based on novel conduction cooling...
