Keyword: radio-frequency
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MOPMB019 Numerical Calculations of Superheating Field in Superconductors with Nanostructured Surfaces cavity, simulation, SRF, superconductivity 114
 
  • M.R.P. Walive Pathiranage
    VMI, Lexington, USA
  • A.V. Gurevich
    ODU, Norfolk, Virginia, USA
 
  Funding: This work was supported by DOE under Grant DE-SC 100387-020 and by Virginia Military Institute (VMI) under Jackson-Hope Grant for faculty travel and for New Directions in Teaching and Research Grants.
We report calculations of a dc superheating field Hs in superconductors with nanostructured surfaces. Particularly, we performed numerical simulations of the Ginzburg-Landau (GL) equations for a superconductor with an inhomogeneous profile of impurity concentration, a thin superconducting layer on top of another superconductor, and S-I-S multilayers. The superheating field was calculated taking into account the instability of the Meissner state at a finite wavelength along the surface depending on the value of the GL parameter. Simulations were done for the materials parameters of Nb and Nb₃Sn at different values of the GL parameter and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of superconducting layers in S-I-S structures can be optimized to reach the maximum Hs, which exceeds the bulk superheating fields of both Nb and Nb₃Sn. For example, a S-I-S structure with 90 nm thick Nb₃Sn layer on Nb can boost the superheating field up to ~ 500 mT, while protecting the SRF cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.
 
poster icon Poster MOPMB019 [1.214 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB019  
About • Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 16 July 2023
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MOPMB021 Correlating Lambda Shift Measurements with RF Performance in Mid-T Heat Treated Cavities cavity, SRF, niobium, ECR 124
 
  • R. Ghanbari, G.K. Deyu, W. Hillert, R. Monroy-Villa, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • C. Bate, D. Reschke, L. Steder, J.C. Wolff
    DESY, Hamburg, Germany
 
  Funding: This work was supported by the BMBF under the research grants 05K19GUB and 05H2021.
Heat treatment procedures have been identified as cru-cial for the performance of niobium SRF cavities, which are the key technology of modern accelerators. The so called "mid-T heat treatments", invert the dependence of losses on the applied accelerating field (anti-Q slope) and significantly reduce the absolute value of losses. The mechanism behind these improvements is still under investigation, and further research is needed to fully understand the principle processes involved. Anomalies in the frequency shift near the transition temperature (Tc), known as "dip" can provide insight into fundamental material properties and allow us to study the relation-ship of frequency response with surface treatments. Therefore, we have measured the frequency versus temperature of multiple mid-T heat treated cavities with different recipes and studied the correlation of SRF properties with frequency shift features. The maximum quality factor correlates with two such shift features, namely the dip magnitude per temperature width and the total frequency shift.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB021  
About • Received ※ 20 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 15 August 2023
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MOPMB024 Flux Expulsion Studies of Niobium Material of 650 MHz Cavities for PIP-II cavity, niobium, simulation, factory 141
 
  • K.E. McGee
    FRIB, East Lansing, Michigan, USA
  • F. Furuta, M. Martinello, O.S. Melnychuk, A.V. Netepenko, G. Wu, Y. Xie
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Two different vendors supplied the niobium sheet material for PIP-II 5-cell 650 MHz cavities, which was characterized by multiple different ASTM sizes. Cavities subsequently fabricated from these sheets were heat-treated at various temperatures, then the cavities’ flux-expulsion performance was measured. Where the initial measurements of vendor O materials showed that nearly all flux remained trapped despite a high thermal gradient, 900C heat treatment subsequently improved the flux expulsion to an acceptable rate. Understanding and characterizing vendor O materials in this way is key for upcoming and future projects planning to employ niobium sheet from this supplier.
 
poster icon Poster MOPMB024 [4.064 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB024  
About • Received ※ 26 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 19 August 2023 — Issue date ※ 21 August 2023
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MOPMB030 Medium Temperature Furnace Baking of Low-beta 650 MHz Five-cell Cavities cavity, niobium, SRF, multipactoring 158
 
  • G. Wu, S.K. Chandrasekaran, V. Chouhan, G.V. Eremeev, F. Furuta, K.E. McGee, A.A. Murthy, A.V. Netepenko, J.P. Ozelis, H. Park, S. Posen
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Medium Temperature baking of low beta 650 MHz cavities was conducted in a UHV furnace. A systematic study of cavity surface resistance components, residual and BCS, was conducted, including analyzing surface resistance due to trapped magnetic flux. Cavities showed an average 4.5 nano-ohm surface resistance at 17 MV/m under 2 K, which meets PIP-II specifications with a 40% margin. The results provided helpful information for the PIP-II project to optimize the cavity processing recipe for cryomodule application. The results were compared to the 1.3 GHz cavity that received a similar furnace baking.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB030  
About • Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 18 July 2023
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MOPMB032 The Collaborative Effects of Intrinsic and Extrinsic Impurities in Low RRR SRF Cavities cavity, SRF, niobium, accelerating-gradient 162
 
  • K. Howard, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia, A. Grassellino
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The SRF community has shown that introducing certain impurities into high-purity niobium can improve quality factors and accelerating gradients. We question why some impurities improve RF performance while others hinder it. The purpose of this study is to characterize the impurity profile of niobium coupons with a low residual resistance ratio (RRR) and correlate these impurities with the RF performance of low RRR cavities so that the mechanism of impurity-based improvements can be better understood and improved upon. The combination of RF testing and material analysis reveals a microscopic picture of why low RRR cavities experience low BCS resistance behavior more prominently than their high RRR counterparts. We performed surface treatments, low temperature baking and nitrogen-doping, on low RRR cavities to evaluate how the intentional addition of oxygen and nitrogen to the RF layer further improves performance through changes in the mean free path and impurity profile. The results of this study have the potential to unlock a new understanding on SRF materials and enable the next generation of high Q/high gradient surface treatments.
 
poster icon Poster MOPMB032 [1.444 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB032  
About • Received ※ 21 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 23 July 2023
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MOPMB036 Magnetic Field Mapping of a Large-Grain 1.3 GHz Single-Cell Cavity cavity, niobium, SRF, cryogenics 172
 
  • I.P. Parajuli, J.R. Delayen, A.V. Gurevich
    ODU, Norfolk, Virginia, USA
  • G. Ciovati
    JLab, Newport News, Virginia, USA
 
  Funding: This work was supported by the National Science Foundation under Grant No. PHY 100614-010. G.C. is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A new magnetic field mapping system for 1.3 GHz single-cell cavities was developed in order to reveal the impact of ambient magnetic field and temperature gradients during cool-down on the flux trapping phenomenon. Measurements were done at 2 K for different cool-down conditions of a large-grain cavity before and after 120 °C bake. The fraction of applied magnetic field trapped in the cavity walls was ~ 50% after slow cool-down and ~20% after fast cool-down. The results showed a weak correlation between between trapped flux locations and hot-spots causing the high-field Q-slope. The results also showed an increase of the trapped flux at the quench location, after quenching, and a local redistribution of trapped flux with increasing RF field.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB036  
About • Received ※ 15 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 05 July 2023
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MOPMB037 Exploration of Parameters that Affect High Field Q-Slope cavity, niobium, accelerating-gradient, SRF 178
 
  • K. Howard, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia, A. Grassellino
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The onset of high field Q-slope (HFQS) around 25 MV/m prevents cavities in electropolished (EP) condition from reaching high quality factors at high gradients due to the precipitation of niobium hydrides during cooldown. These hydrides are non-superconducting at 2 K, and contribute to losses such as Q disease and HFQS. We are interested in exploring the parameters that affect the behavior of HFQS. We study a high RRR cavity that received an 800 C by 3 hour bake and EP treatment to observe HFQS. First, we explore the effect of trapped magnetic flux. The cavity is tested after cooling slowly through Tc while applying various levels of ambient field. We observe the onset of the HFQS and correlate this behavior with the amount of trapped flux. Next, we investigate the effect of the size/concentration of hydrides. The cavity is tested after holding the temperature at 100 K for 12 hours during the cooldown to promote the growth of hydrides. We can correlate the behavior of the HFQS with the increased hydride concentration. Our results will help further the understanding of the mechanism of HFQS.
 
poster icon Poster MOPMB037 [1.648 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB037  
About • Received ※ 12 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 19 August 2023
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MOPMB040 Comparing the Effectiveness of Low Temperature Bake in EP and BCP Cavities cavity, SRF, niobium, factory 187
 
  • H. Hu, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Electropolishing (EP) and buffered chemical polishing (BCP) are conventional surface preparation techniques for superconducting radiofrequency (SRF) cavities. Both EP and BCP treated SRF cavities display high field Q-slope (HFQS) which degrades performance at high gradients. While high gradient performance in EP cavities can be improved by introducing oxygen via a low temperature bake (LTB) of 120°C by 48 hours, LTB does not consistently remove HFQS in BCP cavities. There is no consensus as to why LTB is not effective on BCP prepared cavities. We examine quench in EP, BCP, EP+LTB, and BCP+LTB treated 1.3 GHz single-cell Nb cavities by studying the heating behavior with field using a temperature mapping system. Cavity performance is correlated to characterizations of surface impurity profile obtained via time of flight secondary ion mass spectrometry studies. We observe a difference in near surface hydrogen concentration following BCP compared to EP that may suggest that the causes of quench in EP and BCP cavities are different.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB040  
About • Received ※ 14 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
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MOPMB041 Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments cavity, ECR, SRF, niobium 191
 
  • S. Balachandran, P. Dhakal, A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
  • T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
  • S. Chetri, P.J. Lee
    NHMFL, Tallahassee, Florida, USA
  • Z.L. Thune
    MSU, East Lansing, USA
 
  Funding: Jefferson Science Associates, LLC under U.S. DOE Grant DEAC05-06OR23177, U.S. DOE, Office of HEP under Grant DE-SC0009960, and NHMFL through NSF Grant DMR-1644779 and the State of Florida.
Bulk Nb for TESLA shaped SRF cavities is a mature technology. Significant advances are in order to push Q0’s to 1010-11(T= 2K), and involve modifications to the sub-surface Nb layers by impurity doping. In order to achieve the lowest surface resistance any trapped flux needs to be expelled for cavities to reach high Q0’s. There is clear evidence that cavities fabricated from polycrystalline sheets meeting current specifications require higher temperatures beyond 800 °C leads to better flux expulsion, and hence improves Q0. Recently, cavities fabricated with a non-traditional Nb sheet with initial cold work due to cold rolling expelled flux better after 800 °C/3h heat treatment than cavities fabricated using fine-grain poly-crystalline Nb sheets. Here, we analyze the microstructure development in Nb from the vendor supplied cold work non- annealed sheet that was fabricated into an SRF cavity as a function of heat treatment building upon the methodology development to analyze microstructure being developed by the FSU-MSU-UT, Austin-JLAB collaboration. The results indicate correlation between full recrystallization and better flux expulsion.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB041  
About • Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 July 2023
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MOPMB042 Evaluation of Flux Expulsion and Flux Trapping Sensitivity of SRF Cavities Fabricated from Cold Work Nb Sheet with Successive Heat Treatment cavity, SRF, niobium, ECR 197
 
  • B.D. Khanal
    ODU, Norfolk, Virginia, USA
  • P. Dhakal
    JLab, Newport News, Virginia, USA
 
  Funding: The work is partially supported by DOE HEP under Awards No. DE-SC 0009960. This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The main source of RF losses leading to lower quality factor of superconducting radio-frequency cavities is due to the residual magnetic flux trapped during cool-down. The loss due to flux trapping is more pronounced for cavities subjected to impurities doping. The flux trapping and its sensitivity to rf losses are related to several intrinsic and extrinsic phenomena. To elucidate the effect of re-crystallization by high temperature heat treatment on the flux trapping sensitivity, we have fabricated two 1.3 GHz single cell cavities from cold-worked Nb sheets and compared with cavities made from standard fine-grain Nb. Flux expulsion ratio and flux trapping sensitivity were measured after successive high temperature heat treatments. The cavity made from cold worked Nb showed better flux expulsion after 800 C/3h heat treatment and similar behavior when heat treated with additional 900 C/3h and 1000 C/3h. In this contribution, we present the summary of flux expulsion, trapping sensitivity, and RF results.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB042  
About • Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 04 July 2023
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MOPMB043 Characterization of Dissipative Regions of an N-Doped SRF Cavity cavity, niobium, electron, experiment 202
 
  • E.M. Lechner, G. Ciovati
    JLab, Newport News, Virginia, USA
  • G. Ciovati, A.V. Gurevich, J. Makita
    ODU, Norfolk, Virginia, USA
  • M. Iavarone, E.M. Lechner, B.D. Oli
    Temple University, Philadelphia, USA
 
  Funding: DE-AC05-06OR23177 NSF Award No. 1734075 W911NF-16-2-0189
We report scanning tunneling microscopy measurements on N-doped cavity hot and cold spot cutouts. Analysis of the electron tunneling spectra using a proximity effect theory shows that hot spots have a reduced superconducting gap and a wider distribution of the contact resistance. Alone, these degraded superconducting properties account for a much weaker excess dissipation as compared with the vortex contribution. Based on the correlation between the quasiparticle density of states and temperature mapping, we suggest that degraded superconducting properties may facilitate vortex nucleation or settling of trapped flux during cooling the cavity through the critical temperature.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB043  
About • Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 13 July 2023
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MOPMB045 Quench Detection in a Superconducting Radio Frequency Cavity with Combined Temperature and Magnetic Field Mapping cavity, niobium, SRF, ECR 211
 
  • B.D. Khanal, G. Ciovati
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, P. Dhakal
    JLab, Newport News, Virginia, USA
 
  Funding: This is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Local dissipation of rf power in SRF cavities create so called ’hot-spots’, primary precursors of cavity quench driven by either thermal or magnetic instability. These hot spots are may be detected by a temperature mapping system, and a large increase in temperature on the outer surface is detected during cavity quench events. Here, we have used combined magnetic and temperature mapping systems using anisotropic magneto-resistance sensors and carbon resisters to locate the hot spots and areas with high trapped flux on a 3 GHz single-cell Nb cavity during the rf tests at 2 K. The effect of global and localized flux trapping on the rf performance will be presented.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB045  
About • Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 12 August 2023
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MOPMB076 Surface Characterization Studies of Gold-Plated Niobium niobium, cavity, controls, site 290
 
  • S.G. Seddon-Stettler, M. Liepe, T.E. Oseroff, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • N. Sitaraman
    Cornell University, Ithaca, New York, USA
 
  Funding: The National Science Foundation, Grant No. PHY-1549132
The native niobium oxide layer present on niobium has been shown to affect the performace of superconducting RF cavities. Extremely thin layers of gold on the surface of niobium have the potential to suppress surface oxidation and improve cavity performance. However, depositing uniform layers of gold at the desired thickness (sub-nm) is difficult, and different deposition methods may have different effects on the gold surface, on the niobium surface, and on the interface between the two. In particular, the question of whether gold deposition actually passivates the niobium oxide is extremely relevant for assessing the potential of gold deposition to improve RF performance. This work builds on previous research studying the RF performance of gold/niobium bilayers with different gold layer thicknesses. We here consider alternative methods to characterize the composition and chemical properties of gold/niobium bilayers to supplement the previous RF study.
 
poster icon Poster MOPMB076 [1.536 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB076  
About • Received ※ 25 June 2023 — Revised ※ 27 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
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MOPMB094 Design of a 1.3 GHz High-Power RF Coupler for Conduction-Cooled Systems cavity, SRF, cryomodule, operation 342
 
  • N.A. Stilin, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell is designing a new standalone, compact SRF cryomodule which uses cryocoolers in place of liquid helium for cooling. One of the biggest challenges in implementing such a system is designing a high-power input coupler which is able to be cooled by the cryocoolers without any additional liquid cryogenics. Due to the limited heat load capacity of the cryocoolers at 4.2 K, this requires very careful thermal isolation of the 4.2 K portion of the coupler and thorough optimization of the RF behavior to minimize losses. This paper will present the various design considerations which enabled the creating of a conduction-cooled 1.3 GHz input coupler capable of delivering up to 100 kW CW RF power.  
poster icon Poster MOPMB094 [0.964 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB094  
About • Received ※ 16 June 2023 — Revised ※ 26 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 23 July 2023
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TUPTB014 Development of Nb₃Sn Coating System and RF Measurement Results at KEK cavity, SRF, accelerating-gradient, controls 414
 
  • H. Ito, H. Sakai, K. Umemori, T. Yamada
    KEK, Ibaraki, Japan
  • K. Takahashi
    Sokendai, Ibaraki, Japan
 
  We have constructed an Nb₃Sn cavity coating system based on the Sn vapor diffusion method. After the construction, improvement of our coating system and environment has been conducted through sample and cavity coating research. Our cavity achieves a Q-value above 1E10 at 4 K after improvement. We will report on the detail of improvement on our coating system and RF measurement results of single-cell Nb₃Sn cavity.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB014  
About • Received ※ 18 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 28 June 2023
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TUPTB039 Simulation of High Pressure Rinse in Superconducting Radio Frequency Cavities cavity, simulation, SRF, site 496
 
  • B.E. Gower, K. Elliott, E.S. Metzgar, T. Xu
    FRIB, East Lansing, Michigan, USA
 
  Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics. Resources of the Facility for Rare Isotope Beams, a DOE Office of Science User Facility, under Award Number DE-SC0000661.
The finish of radio frequency (RF) surfaces inside superconducting RF (SRF) cavities is of utmost importance as it dictates ultimate cavity performance. After the cavity surfaces have undergone chemical etching, polishing, and hydrogen degassing, the final step in surface preparation involves cleaning using a high pressure rinse (HPR) with ultra-high purity water (UPW) to remove any residue from the previous chemical processes. The complex surface geometry of cavities poses difficulties in achieving effective and thorough HPR cleaning. This study introduces a versatile simulation tool created in MATLAB, which has the potential to be applied to various SRF cavities. The detail of the algorithm used and nozzle and motion setup will be described using an FRIB 0.53 half wave resonator (HWR) cavity as an example.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB039  
About • Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 07 July 2023
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TUPTB052 A Novel Manufacture of Niobium SRF Cavities by Cold Spray cavity, SRF, niobium, experiment 545
 
  • M. Yamanaka
    KEK, Ibaraki, Japan
  • K. Shimada
    Nihon University, College of Engineering, Koriyama, Japan
 
  Cold spray is a lower-temperature solid-state thermal spray process that deposits metal powder using a heated inert gas through a supersonic nozzle. When the material hits at supersonic speed and reaches the critical speed, the particles themselves are plastically deformed to form a film. The material of the superconducting cavity is niobium, a very expensive rare metal. To reduce the amount of niobium and the cost, we propose a novel manufacturing method of forming a thick niobium film on the surface of a mandrel by cold spray using niobium powder and removing the mandrel to finish a hollow shape. We confirmed the feasibility of the proposed method using a model similar to a 3.9 GHz one-cell cavity. Also, the RRR measurement of the niobium specimen made by cold spray was carried out and the measured value of 11 was obtained. We report on these results.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB052  
About • Received ※ 17 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 10 July 2023
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WEIXA05 Electropolishing Study on Nitrogen-Doped Niobium Surface cavity, niobium, SRF, cathode 641
 
  • V. Chouhan, T.J. Ring, G. Wu
    Fermilab, Batavia, Illinois, USA
  • E.A.S. Viklund
    NU, Evanston, Illinois, USA
 
  The nitrogen doping (N-doping) process is applied to niobium (Nb) superconducting cavities to enhance their quality factors. The N-doping is followed by an electropolishing process that provides the final surface of the cavities. A controlled EP process is necessary to get the benefit of N-doping and achieve a high accelerating gradient. We have performed electropolishing of N-doped Nb surface under various conditions to understand their impact on the surface. A modified EP process was developed to obtain a smooth pit-free surface.  
slides icon Slides WEIXA05 [17.622 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA05  
About • Received ※ 19 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
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WEPWB052 Temperature, RF Field, and Frequency Dependence Performance Evaluation of Superconducting Niobium Half-Wave Coaxial Cavity cavity, niobium, SRF, experiment 691
 
  • N.K. Raut, G. Ciovati, P. Dhakal
    JLab, Newport News, Virginia, USA
  • S.U. De Silva, J.R. Delayen, B.D. Khanal, J.K. Tiskumara
    ODU, Norfolk, Virginia, USA
 
  Funding: This is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177
Recent advancement in superconducting radio frequency cavity processing techniques, with diffusion of impurities within the RF penetration depth, resulted in high quality factor with increase in quality factor with increasing accelerating gradient. The increase in quality factor is the result of a decrease in the surface resistance as a result of nonmagnetic impurities doping and change in electronic density of states. The fundamental understanding of the dependence of surface resistance on frequency and surface preparation is still an active area of research. Here, we present the result of RF measurements of the TEM modes in a coaxial half-wave niobium cavity resonating at frequencies between 0.3 - 1.3 GHz. The temperature dependence of the surface resistance was measured between 4.2 K and 1.6 K. The field dependence of the surface resistance was measured at 2.0 K. The baseline measurements were made after standard surface preparation by buffered chemical polishing.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB052  
About • Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 20 July 2023
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WEPWB125 Thermodynamic Properties of Srf Niobium cavity, SRF, niobium, cryogenics 884
 
  • P. Dhakal
    JLab, Newport News, Virginia, USA
 
  Funding: This is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177.
Bulk and thin films of niobium are the materials of choice in fabricating superconducting radio frequency (SRF) cavities for modern particle accelerators and quantum computing applications. The thermodynamic properties of Nb are of particular interest in heat management in cryogenic environments. Here, we report the results of measurements of the thermodynamic properties of niobium used in the fabrication of superconducting radio frequency (SRF) cavities. The temperature and magnetic field dependence of thermal conductivity, Seebeck coefficient, and specific heat capacity was measured on bulk niobium samples.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB125  
About • Received ※ 11 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 July 2023
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THIXA05 Conduction-Cooled SRF Cavities: Opportunities and Challenges cavity, SRF, operation, cryomodule 973
 
  • N.A. Stilin, H. Conklin, T. Gruber, A.T. Holic, M. Liepe, T.I. O’Connell, P. Quigley, J. Sears, V.D. Shemelin, J. Turco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Thanks to improvements in the performance of both commercial cryocoolers and Nb₃Sn-coated superconducting radio-frequency (SRF) cavities, it is now possible to design and build compact, SRF cryomodules without the need for liquid cryogenics. In addition, these systems offer robust, non-expert, turn-key operation, making SRF technology significantly more accessible for smaller-scale applications in fields such as industry, national security, medicine, environmental sustainability, etc. To fully realize these systems, many technical and operational challenges must be overcome. These include properly cooling the SRF cavity via thermal conduction and designing high-power (~ 100 kW continuous) RF couplers which dissipate minimal heat (~ 1 W) at 4.2 K. This presentation will discuss these challenges and the solutions which have been developed at Cornell University and elsewhere.  
slides icon Slides THIXA05 [7.219 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-THIXA05  
About • Received ※ 27 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 04 July 2023 — Issue date ※ 08 July 2023
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