TUIXA —  SRF Technology I   (27-Jun-23   10:40—12:20)
Paper Title Page
TUIXA01
Understanding the Field and Frequency Dependence of Rf Loss in SRF Cavities  
 
  • P. Dhakal, G. Ciovati
    JLab, Newport News, Virginia, USA
  • G. Ciovati, A.V. Gurevich, B.D. Khanal
    ODU, Norfolk, Virginia, USA
 
  Funding: This is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177.
SRF cavities subjected to heat treatment below 200 °C in the presence of nitrogen showed an improvement in quality factor while maintaining an accelerating gradient above 25 MV/m. Here, we report the rf performance of several single-cell superconducting radio frequency cavities with frequency ranging from 0.75 - 3.0 GHz subjected to low temperature heat treatment in nitrogen environment. The cavities were treated at temperature 120 - 175 oC for 24 - 48 hours in low partial pressure of ultra-pure nitrogen gas. The improvement in Q₀ with Q-rise was observed when nitrogen gas was injected ~300 °C during the furnace treatment. The surface modification was confirmed by the change in electronic mean free path and near surface elemental analysis by SIMS. The field dependence of the rf losses is strongly correlated to the cavity frequency. The analysis of experimental data with available theoretical models as well as comparison with similar study on high temperature nitrogen doped cavities will be presented.
 
slides icon Slides TUIXA01 [4.416 MB]  
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TUIXA02
The Role of Nitrogen and Other Impurities in SRF Cavity Performance  
 
  • 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.
Bulk niobium SRF cavities remain as a leading technology in the realization of the next generation of particle accelerators and serve as the highest Q₀ platform for 3-D quantum computing architectures. Whether utilized in kilometer long accelerators or 10 cm long quantum processors, the performance of these cavities is largely determined by the material properties within the 100 nm from the inner RF surface. This talk will discuss advancements made in the development and understanding of surface engineering techniques (doping with O or N, N-infusion, and low/mid temperature baking) on niobium SRF cavities in different regimes: mK and single photon levels for quantum computing and high Q/high G accelerator applications. By coupling material science and resonator measurements, we delineate the role of different impurities in enabling excellent performance in each of these regimes.
 
slides icon Slides TUIXA02 [6.669 MB]  
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TUIXA03
Surface Resistance and Trapped Flux Sensitivity as Function of Baking Temperature  
 
  • H. Ito, H. Araki, K. Umemori
    KEK, Ibaraki, Japan
 
  We have investigated the influence of furnace baking at various baking temperatures on Q-value and trapped flux sensitivity. We find that mid-temperature baking is a promising process for obtaining a high Q-value, but it results in a high flux sensitivity. In particular, 300°C baking results in extremely high Q-value and sensitivity. Instead, 250°C baking is found to be a more effective process than 300°C baking for accelerator applications, as it can reach a higher accelerating gradient while keeping a high Q-value and a lower sensitivity. In addition, we find that 200°C baking can reach a higher Q-value at a high accelerating gradient e.g. 35 MV/m compared to 120°C 48 h baking that is applied to the cavity normally.  
slides icon Slides TUIXA03 [32.219 MB]  
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TUIXA04 First Results from beta-SRF- Testing SRF Samples at High Parallel Field 374
 
  • E. Thoeng, R. Kiefl, W.A. MacFarlane, J.O. Ticknor
    UBC & TRIUMF, Vancouver, British Columbia, Canada
  • M. Asaduzzaman, S.R. Dunsiger, D. Fujimoto, T. Junginger, V.L. Karner, P. Kolb, R.E. Laxdal, R. Li, R.M.L. McFadden, G. Morris, M. Stachura
    TRIUMF, Vancouver, Canada
  • T. Junginger, R.M.L. McFadden
    UVIC, Victoria, Canada
 
  The new ¿-SRF facility at TRIUMF has recently been commissioned. A new 1 m extension has been added to an existing ¿-NMR beamline with a large Helmholtz coil to produce fields up to 200 mT parallel to sample surfaces. The ¿-NMR technique allows depth dependent characterization of the local magnetic field in the first 100 nm of the sample surface making the probe ideal for studying Meissner screen- ing in heat treated Niobium or layered SRF materials. First measurements of Meissner screening at fields up to 200 mT have been analyzed. The results show clear differences in the Meissner screening of baseline treatments compared to mid-T baked (O-doped) Niobium.  
slides icon Slides TUIXA04 [1.644 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIXA04  
About • Received ※ 24 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 06 July 2023 — Issue date ※ 09 July 2023
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TUIXA05
Energy Barrier at Superconductor-Superconductor Interfaces  
 
  • T. Junginger
    UVIC, Victoria, Canada
 
  Funding: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through grants SAPPJ-2020-00030 and SAPIN-2021-00032.
In SUST 30 (12), 125012, we reported that coating a superconductor with a larger penetration depth on niobium can increase the field of first vortex penetration Hvp from niobium¿s lower critical field Hc1 to its superheating field Hsh. This was interpreted as an energy barrier at the superconductor-superconductor interface, analogous to the Bean-Livingston barrier at vacuum-superconductor interfaces. A smaller but significant increase in Hvp was observed for low-temperature baked (LTB) niobium. Results from muon spin rotation with variable implantation depth in the micrometer range and vibrating sample magnetometry (Scientific Reports 12 (1), 5522) suggest that the apparent Hvp increase in LTB niobium was due to surface pinning and not an actual Hvp increase. Low-energy muon spin rotation results further support that interpretation as a distinct bipartite magnetic screening profile is observed for actual bilayers (arXiv:2304.09360) but not for LTB niobium (PR Applied 19 (4), 044018 and arXiv:2305.02129). This suggests that the reason why some LTB niobium SRF cavities reach surface magnetic fields beyond Hc1 is specific to RF effects, such as the nucleation time.
 
slides icon Slides TUIXA05 [0.997 MB]  
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