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MOPMB021 Correlating Lambda Shift Measurements with RF Performance in Mid-T Heat Treated Cavities 124
SUSPB010   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB042 Evaluation of Flux Expulsion and Flux Trapping Sensitivity of SRF Cavities Fabricated from Cold Work Nb Sheet with Successive Heat Treatment 197
SUSPB015   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB045 Quench Detection in a Superconducting Radio Frequency Cavity with Combined Temperature and Magnetic Field Mapping 211
SUSPB016   use link to see paper's listing under its alternate paper code  
 
  • 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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WEIXA04 Development of the Directly-Sliced Niobium Material for High Performance SRF Cavities 634
 
  • A. Kumar, H. Araki, T. Dohmae, H. Ito, T. Saeki, K. Umemori, A. Yamamoto, M. Yamanaka
    KEK, Ibaraki, Japan
  • A. Yamamoto
    CERN, Meyrin, Switzerland
 
  For the purpose of cost reduction for the ILC, KEK has been conducting R&D on direct sliced Nb materials such as large grain and medium grain Nb. Single-cell, 3-cell, and 9-cell cavities have been manufactured, and each has demonstrated a high-performance accelerating gradient exceeding 35 MV/m. The results of applying high-Q/high-G recipes, such as two-step baking and furnace baking to these cavities are also shown. Moreover, mechanical tests have been carried out for the beforementioned materials to evaluate their strength for application to the High-Pressure Gas Safety Law. The status of development of these large grain and Medium grain Nb will be presented.  
slides icon Slides WEIXA04 [3.773 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEIXA04  
About • Received ※ 18 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 12 July 2023
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WEPWB065 Impact of Medium Temperature Heat Treatments on the Magnetic Flux Expulsion Behavior of SRF Cavities 731
SUSPB043   use link to see paper's listing under its alternate paper code  
 
  • J.C. Wolff, J. Eschke, A. Gössel, K. Kasprzak, D. Reschke, L. Steder, L. Trelle, M. Wiencek
    DESY, Hamburg, Germany
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
 
  Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program.
Medium temperature (mid-T) heat treatments at 300 °C are used to enhance the intrinsic quality factor of superconducting radio frequency (SRF) cavities. Unfortunately, such treatments potentially increase the sensitivity to trapped magnetic flux and consequently the surface resistance of the cavity. For this reason, it is crucial to maximize the expulsion of magnetic flux during the cool down. The flux expulsion behavior is next to the heat treatment mainly determined by the geometry, the niobium grain size and the grain orientation. However, it is also affected by parameters of the cavity performance tests like the cool down velocity, the spatial temperature gradient along the cavity surface and the magnetic flux density during the transition of the critical temperature. To improve the flux expulsion behavior and hence the efficiency of future accelerator facilities, the impact of these adjustable parameters as well as the mid-T heat treatment on 1.3 GHz TESLA-Type single-cell cavities is investigated by a new approach of a magnetometric mapping system. In this contribution first performance test results of cavities before- and after mid-T heat treatment are presented.
 
poster icon Poster WEPWB065 [3.077 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB065  
About • Received ※ 21 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 13 July 2023
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WEPWB111 A New Ultra-High Vacuum Furnace for SRF R&D 855
 
  • M. Wenskat, C. Bate
    DESY, Hamburg, Germany
  • C. Bate, C. Martens
    University of Hamburg, Hamburg, Germany
  • R. Ghanbari, W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
 
  Funding: This work was supported by the BMBF under the research grants 05K19GUB and 05H2021.
A new vacuum furnace has been designed and purchased by the University of Hamburg and is operating in an ISO5 cleanroom. This furnace can anneal single-cell TESLA cavities at temperatures up to 1000°C and with a pressure of less than 10-7mbar or in a nitrogen atmosphere of up to 10-2mbar. We will lay out the underlying design ideas, based on the gained experience from our previous annealing research, and present the commissioning of the furnace itself. Additionally, we will show for the first time the results of sample and cavity tests after annealing in the furnace. This will be accompanied by an overview of the intended R&D process and scientific questions to be addressed.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB111  
About • Received ※ 21 June 2023 — Revised ※ 15 July 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
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WEPWB116 The Influence of Sample Preparation, Soak Time, and Heating Rate on Measured Recrystallization of Deformed Polycrystalline Niobium 863
 
  • Z.L. Thune
    MSU, East Lansing, USA
  • T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
 
  Funding: DOE/OHEP (Grant Number: DE-SC0009960)
Improving accelerator performance relies on consistent production of high-purity niobium superconducting radiofrequency (SRF) cavities. Current production uses an 800 °C 3 hr heat treatment, but 900-1000 °C can improve cavity performance via recrystallization (Rx) and grain growth. As Rx is thermally activated, increasing the temperature and/or the heating rate could facilitate a reduction in geometrically necessary dislocation (GND) density that is associated with the degradation of cavity performance via trapped magnetic flux. Recent work shows that increasing the annealing temperature increased the Rx fraction in cold-rolled polycrystalline niobium. However, the influence of heating rate on the extent of Rx was minimal with a 3 hr soak time. To further assess the influence of heating rate on measured Rx, as well as the effects of sample preparation, electron backscatter diffraction (EBSD) was used to quantify the extent of Rx on samples annealed at a single temperature with different soak times. Comparing samples with different surface preparation shows that pinned grain boundaries on the free surface reveal a much smaller grain size than below the surface.
* Z.L. Thune et al., "The Influence of Strain Path and Heat Treatment Variations on Recrystallization in Cold-Rolled High-Purity Niobium Polycrystals," doi: 10.1109/TASC.2023.3248533.
 
poster icon Poster WEPWB116 [1.312 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB116  
About • Received ※ 23 June 2023 — Revised ※ 26 June 2023 — Accepted ※ 20 August 2023 — Issue date ※ 21 August 2023
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WEPWB120 Flux Expulsion Testing for LCLS-II-HE Cavity Production 876
 
  • J.T. Maniscalco, S. Aderhold, M. Checchin, D. Gonnella, R.D. Porter
    SLAC, Menlo Park, California, USA
  • T.T. Arkan, D. Bafia, J.A. Kaluzny, S. Posen
    Fermilab, Batavia, Illinois, USA
  • M.E. Bevins, A.J. Grabowski, J. Hogan, C.E. Reece, D. Savransky, H. Vennekate
    JLab, Newport News, Virginia, USA
 
  Nitrogen-doped niobium SRF cavities are sensitive to trapped magnetic flux, which decreases the cavity intrinsic Q₀. Prior experimental results have shown that heat treatments to 900°C and higher can result in stronger flux expulsion during cooldown; the precise temperature required tends to vary by vendor lot/ingot of the niobium material used in the cavity cells. For LCLS-II-HE, to ensure sufficient flux expulsion in all cavities, we built and tested single-cell cavities to determine this required temperature for each vendor lot of niobium material to be used in cavity cells. In this report, we present the results of the single-cell flux expulsion testing and the Q₀ of the nine-cell cavities built using the characterized vendor lots. We discuss mixing material from different vendor lots, examine the lessons learned, and finally present an outlook on possible refinements to the single-cell technique.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB120  
About • Received ※ 15 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 03 July 2023 — Issue date ※ 13 July 2023
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WEPWB121 Niobium Chronicles: Surface Quality Investigation and Recovery During Material Procurement for the PIP-II High Beta 650 MHz Cavities 880
 
  • A.D. Shabalina
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
 
  The surface quality of high-purity niobium for superconducting radiofrequency cavities experienced a sudden and significant decline in 2021. The recovery process and root cause analysis were challenging due to a variety of factors such as COVID-19 travel restrictions, cultural differences, and bureaucratic processes. Effective open communication was crucial to resolving the issue, especially with direct vendor oversight being impossible.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB121  
About • Received ※ 28 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 20 August 2023 — Issue date ※ 20 August 2023
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WEPWB125 Thermodynamic Properties of Srf Niobium 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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WEPWB126 First Results from Nanoindentation of Vapor Diffused Nb₃Sn Films on Nb 888
 
  • U. Pudasaini
    JLab, Newport News, Virginia, USA
  • S. Cheban, G.V. Eremeev
    Fermilab, Batavia, Illinois, USA
 
  Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics & Office of High Energy Physics.
The mechanical vulnerability of the Nb₃Sn-coated cavities is identified as one of the significant technical hurdles toward deploying them in practical accelerator applications in the not-so-distant future. It is crucial to characterize the material’s mechanical properties in ways to address such vulnerability. Nanoindentation is a widely used technique for measuring the mechanical properties of thin films that involves indenting the film with a small diamond tip and measuring the force-displacement response to calculate the film’s elastic modulus, hardness, and other mechanical properties. The nanoindentation analysis was performed on multiple vapor-diffused Nb₃Sn samples coated at Jefferson Lab and Fermilab coating facilities for the first time. This contribution will discuss the first results obtained from the nanoindentation of Nb₃Sn-coated Nb samples prepared via the Sn vapor diffusion technique.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB126  
About • Received ※ 19 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 16 July 2023
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