SRF2023 - List of Keywords (ECR)

Paper	Title	Other Keywords	Page
MOPMB012	Investigation, Using Nb Foils to Characterise the Optimal Dimensions of Samples Measured by the Magnetic Field Penetration Facility	cavity, SRF, experiment, niobium	88
	L.G.P. Smith, D.A. Turner STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, O.B. Malyshev, D.A. Turner Cockcroft Institute, Warrington, Cheshire, United Kingdom G. Burt Lancaster University, Lancaster, United Kingdom T. Junginger TRIUMF, Vancouver, Canada T. Junginger UVIC, Victoria, Canada O.B. Malyshev STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	SRF cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, E_acc, where E_acc is limited by the maximum magnetic field, Bmax, that can be applied on the surface of the accelerating cavity wall. To increase E_acc, Bmax, which can be applied to the surface, must also be increased. The A15 materials or multilayer structures are the potential solution to increase Bmax. Since coating and RF testing of full size RF cavities is both expensive and time consuming, one need to evaluate new ideas in superconducting thin films quickly and at low cost. A magnetic field penetration experiment has been designed and built at Daresbury Laboratory to test small superconducting samples. The facility produces a parallel DC magnetic field, which applied from one side of the sample to the other similar to that in an RF cavity. The facility applies an increasing magnetic field at a set temperature to determine the field of full flux penetration which can give an insight into the quality and structure of the superconducting structure. The facility has been characterised using both type I and II superconductors and is now producing results from novel materials.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB012
About •	Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 17 July 2023
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MOPMB017	Development of a Thermal Conductance Instrument for Niobium at Cryogenic Temperatures	cavity, niobium, cryogenics, operation	109
	C. Saribal, C. Martens University of Hamburg, Hamburg, Germany W. Hillert, M. Wenskat University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: University of Hamburg Particle accelerators form an important tool in a variety of research fields. In an effort to reduce operation costs while maintaining high energies, their accelerating structures are steadily improved towards higher accelerating fields and lower RF losses. Stable operation of such 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. Pairs of niobium disks are placed inside of a liquid helium bath and a temperature gradient is generated across them to obtain total thermal resistance for temperatures below 2 Kelvin. To get an idea of the instruments sensitivity and how standard cavity treatments influence thermal resistance, samples are tested post fabrication, polishing and 800 °C baking. The first tests show the commissioning of our newly set up system and if it is feasible to observe relevant changes and evaluate new and promising cavity treatments such as SIS structures.
	Poster MOPMB017 [3.217 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB017
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 July 2023
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MOPMB021	Correlating Lambda Shift Measurements with RF Performance in Mid-T Heat Treated Cavities	cavity, SRF, niobium, radio-frequency	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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MOPMB038	Temperature Mapping for Coaxial Cavities at TRIUMF	cavity, SRF, LabView, data-acquisition	183
	P. Kolb, T. Junginger, J.J. Keir, R.E. Laxdal, B. Matheson, Z.Y. Yao TRIUMF, Vancouver, Canada H. Al Hassini, T. Junginger UVIC, Victoria, Canada L. Fearn UW/Physics, Waterloo, Ontario, Canada
	Temperature mapping (T-map) on superconducting radio-frequency (SRF) cavities has been shown as a useful tool to identify defects and other abnormal sources of losses. So far T-map systems have only been realized for elliptical cavities that have an easily accessible outer surface. TEM mode cavities such as quarterwave and halfwave resonators (QWR, HWR) dissipate most of their power on the inner conductor of the coaxial structure. The limited access and constrained space are a challenge for the design of a temperature mapping system. This paper describes the mechanical and electrical design including the data acquisition of a T-map system for the TRIUMF multi-mode coaxial cavities, and first results are shown.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB038
About •	Received ※ 20 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 30 June 2023
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MOPMB041	Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments	cavity, SRF, niobium, radio-frequency	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 10^10-11(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, radio-frequency	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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MOPMB044	Topographic Evolution of Nitrogen Doped Nb Subjected to Electropolishing	SRF, cavity, niobium, vacuum	207
	E.M. Lechner, C.G. Baxley, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA J.W. Angle, M.J. Kelley Virginia Polytechnic Institute and State University, Blacksburg, USA
	Funding: DE-AC05-06OR23177 DE-SC-0014475 Surface quality is paramount in facilitating high perfor-mance SRF cavity operation. Here, we investigate the topographic evolution of samples subjected to N-doping and 600 °C vacuum anneal. We show that in N-doped Nb, niobium nitrides may grow continuously along grain boundaries. Upon electropolishing high slope angle grooves are revealed which sets up a condition that may facilitate a supression of the superheating field.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB044
About •	Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 17 July 2023
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MOPMB045	Quench Detection in a Superconducting Radio Frequency Cavity with Combined Temperature and Magnetic Field Mapping	cavity, radio-frequency, niobium, SRF	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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MOPMB050	Thermal Feedback in Coaxial SRF Cavities	cavity, niobium, feedback, SRF	224
	M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao TRIUMF, Vancouver, Canada T. Junginger UVIC, Victoria, Canada
	Funding: Natural Sciences and Engineering Research Council of Canada The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023
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TUCXA01	Study of the Dynamics of Flux Trapping in Different SRF Materials	experiment, cavity, niobium, controls	380
	F. Kramer, S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany T. Kubo KEK, Ibaraki, Japan
	A dedicated experimental setup to measure magnetic flux dynamics and trapped flux in samples is used to precisely map out how trapped flux is influenced by different parameters. The setup allows for rapid thermal cycling of the sample so that effects of cooldown parameters can be investigated in detail. We show how temperature gradient, cooldown rate, and the magnitude of external field influence trapped flux in large grain, fine grain and coated niobium samples. The detailed measurements show unexpected results, namely that too fast cooldowns increase trapped flux, large grain material traps flux only when the external field is larger than a temperature gradient dependent threshold field, and the measured dependence of trapped flux on temperature gradient does not agree with an existing model. Therefore, a new model is presented which agrees better with the measured results.
	Slides TUCXA01 [3.180 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCXA01
About •	Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 June 2023
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TUPTB002	Modelling Trapped Flux in Niobium	experiment, cavity, niobium, controls	393
	F. Kramer, S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany T. Kubo KEK, Ibaraki, Japan
	Detailed measurements of magnetic flux dynamics and trapped magnetic flux in niobium samples were conducted with a new experimental setup that permits precise control of the cooldown parameters. With this setup the dependency of trapped flux on the temperature gradient, external magnetic field, and cooldown rate can be mapped out in more detail compared to cavity measurements. We have obtained unexpected results, and an existing model describing trapped flux in dependence of temperature gradient does not agree with the measured data. Therefore, a new model is developed which describes the magnitude of trapped flux in dependence of the temperature gradient across the sample during cooldown. The model describes the amount of trapped flux lines with help of a density distribution function of the pinning forces of pinning centers and the thermal force which can de-pin flux lines from pinning centers. The model shows good agreement with the measured data and correctly predicts trapped flux at different external flux densities.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB002
About •	Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 13 July 2023
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TUPTB004	Progress on Zirconium-Doped Niobium Surfaces	niobium, vacuum, electron, superconductivity	398
	N. Sitaraman, T. Arias, Z. Baraissov, D.A. Muller Cornell University, Ithaca, New York, USA G. Gaitan, M. Liepe, T.E. Oseroff, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the NSF under Award PHY-1549132, the Center for Bright Beams, and in part by CNF (NSF Grant NNCI-2025233), and in part by CCMR (DMR-1719875). The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB004
About •	Received ※ 30 June 2023 — Revised ※ 26 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 22 August 2023
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TUPTB020	Surface Properties and RF Performance of Vapor Diffused Nb₃Sn on Nb after Sequential Anneals below 1000 °C	cavity, SRF, electron, experiment	433
	J.K. Tiskumara, J.R. Delayen ODU, Norfolk, Virginia, USA G.V. Eremeev Fermilab, Batavia, Illinois, USA U. Pudasaini JLab, Newport News, Virginia, USA
	Nb₃Sn is a next-generation superconducting material that can be used for future superconducting radiofrequency (SRF) accelerator cavities, promising better performance, cost reduction, and higher operating temperature than Nb. The Sn vapor diffusion method is currently the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Among post-coating treatments to optimize the coating quality, higher temperature annealing without Sn is known to degrade Nb₃Sn because of Sn loss. We have investigated Nb₃Sn/Nb samples briefly annealed at 800-1000 °C, for 10 and 20 minutes to potentially improve the surface to enhance the performance of Nb₃Sn-coated cavities. Following the sample studies, a coated single-cell cavity was sequentially annealed at 900 °C and tested its performance each time, improving the cavity’s quality factor relatively. This paper summarizes the sample studies and discusses the RF test results from sequentially annealed SRF Nb₃Sn/Nb cavity.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB020
About •	Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 07 July 2023
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TUPTB036	Equidistant Optimization of Elliptical SRF Standing Wave Cavities	cavity, SRF, linac, acceleration	480
	V.D. Shemelin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	A record accelerating rate was achieved earlier in standing wave (SW) SRF cavities when their shape was optimized for lower peak surface magnetic field. In view of new materials with higher limiting magnetic fields, expected for SRF cavities, in the first line Nb₃Sn, the approach to optimization of cavity shape should be revised. A method of equidistant optimization, offered earlier for traveling wave cavities is applied to SW cavities. It is shown here that without limitation by magnetic field, the maximal accelerating rate is defined to a significant degree by the cavity shape. For example, for a cavity with the aperture radius Ra = 35 mm the minimal ratio of the peak surface electric field to the accelerating rate is about Epk/E_acc = 1.54. So, with the maximal surface field experimentally achieved E_pk ¿ 125 MV/m, the maximal achievable accelerating rate is about 80 MeV/m even if there are no restrictions by the magnetic field. Another opportunity ¿ optimization for a low magnetic field, is opening for the same material, Nb₃Sn, with the purpose to have a high quality factor and increased accelerating rate that can be used for industrial linacs.
	Poster TUPTB036 [0.787 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB036
About •	Received ※ 15 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 08 July 2023
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WEPWB048	Geometry Optimization for a Quadrupole Resonator at Jefferson Lab	quadrupole, SRF, simulation, cavity	670
	S. Bira, M. Ge, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA L. Vega Cid, W. Venturini Delsolaro CERN, Meyrin, Switzerland
	Funding: This manuscript is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-6OR23177 with Jefferson Science Associates The quadrupole resonator (QPR) is a sample characterization tool to measure the RF properties of superconducting materials using the calorimetry method at different temperatures, magnetic fields, and frequencies. Such resonators are currently operating at CERN and HZB but suffer from Lorentz force detuning and modes overlapping, resulting in higher uncertainties in surface resistance measurement. Using the two CERN’s QPR model iterations, the geometry was optimized via electromagnetic and mechanical simulations to eliminate these issues. The new QPR version was modeled for an increasing range of magnetic fields. The magnetic field is concentrated at the center of the sample to reduce the uncertainty in surface resistance measurements significantly. This paper will discuss the QPR geometry optimization for the new version of QPR, which is now progressing towards fabrication.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB048
About •	Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 19 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	cavity, niobium, SRF, electron	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 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	cavity, cryomodule, niobium, SRF	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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WEPWB128	Experimental Study of Mechanical Dampers for the FRIB β=0.041 Quarter-Wave Resonators	cavity, damping, operation, linac	898
	J. Brown, W. Chang, W. Hartung, S.H. Kim, T. Xu FRIB, East Lansing, Michigan, USA
	Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award numbers DE-SC0018362 and DE-SC0000661 and Michigan State University. The ’pendulum’ mechanical mode of quarter-wave resonators (QWR) often causes an issue with microphonics and/or ponderomotive instability unless otherwise the inner conductors are properly stiffened and/or damped. FRIB QWRs are equipped with a Legnaro-style frictional damper installed inside of the inner conductor such that it counteracts the oscillations of the inner conductor. In cryomodule tests and linac operation, we observed that the damping efficiency is different for a few β=0.041 QWRs. This study aimed to experimentally characterize the damping efficacy as a function of damper mass and surface roughness. We present damping measurements at room temperature and at two different masses and surface roughness as well as discuss future studies for damper re-optimization based on this follow-on study.
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB128
About •	Received ※ 20 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 August 2023
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WEPWB133	Testing of the 2.6 GHz SRF Cavity Tuner for the Dark Photon Experiment at 2 K	cavity, photon, SRF, experiment	907
	C. Contreras-Martinez, B. Giaccone, I.V. Gonin, T.N. Khabiboulline, O.S. Melnychuk, Y.M. Pischalnikov, S. Posen, O.V. Pronitchev, J.C. Yun Fermilab, Batavia, Illinois, USA
	At FNAL two 2.6 GHz SRF cavities are being used to search for dark photons, the experiment can be conducted at 2 K or in a dilution refrigerator. Precise frequency tuning is required for these two cavities so they can be matched in frequency. A cooling capacity constraint on the dilution refrigerator only allows piezo actuators to be part of the design of the 2.6 GHz cavity tuner. The tuner is equipped with three encapsulated piezo that deliver the long- and short-range frequency tuning. Modifications were implemented on the first tuner design due to the low forces on the piezos due to the cavity. Three brass rods with Belleville washers were added to the design to increase the overall force on the piezos. The results at 2 K of testing this tuner with and without the modification will be presented.
	Poster WEPWB133 [0.829 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB133
About •	Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 04 July 2023
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Paper

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Other Keywords

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Investigation, Using Nb Foils to Characterise the Optimal Dimensions of Samples Measured by the Magnetic Field Penetration Facility

cavity, SRF, experiment, niobium

88

L.G.P. Smith, D.A. Turner
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, O.B. Malyshev, D.A. Turner
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt
Lancaster University, Lancaster, United Kingdom
T. Junginger
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada
O.B. Malyshev
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

SRF cavities made of bulk Nb are reaching their theoretical limits in the maximum accelerating gradient, E_acc, where E_acc is limited by the maximum magnetic field, Bmax, that can be applied on the surface of the accelerating cavity wall. To increase E_acc, Bmax, which can be applied to the surface, must also be increased. The A15 materials or multilayer structures are the potential solution to increase Bmax. Since coating and RF testing of full size RF cavities is both expensive and time consuming, one need to evaluate new ideas in superconducting thin films quickly and at low cost. A magnetic field penetration experiment has been designed and built at Daresbury Laboratory to test small superconducting samples. The facility produces a parallel DC magnetic field, which applied from one side of the sample to the other similar to that in an RF cavity. The facility applies an increasing magnetic field at a set temperature to determine the field of full flux penetration which can give an insight into the quality and structure of the superconducting structure. The facility has been characterised using both type I and II superconductors and is now producing results from novel materials.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB012

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Received ※ 18 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 17 July 2023

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MOPMB017

Development of a Thermal Conductance Instrument for Niobium at Cryogenic Temperatures

cavity, niobium, cryogenics, operation

109

C. Saribal, C. Martens
University of Hamburg, Hamburg, Germany
W. Hillert, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: University of Hamburg
Particle accelerators form an important tool in a variety of research fields. In an effort to reduce operation costs while maintaining high energies, their accelerating structures are steadily improved towards higher accelerating fields and lower RF losses. Stable operation of such 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. Pairs of niobium disks are placed inside of a liquid helium bath and a temperature gradient is generated across them to obtain total thermal resistance for temperatures below 2 Kelvin. To get an idea of the instruments sensitivity and how standard cavity treatments influence thermal resistance, samples are tested post fabrication, polishing and 800 °C baking. The first tests show the commissioning of our newly set up system and if it is feasible to observe relevant changes and evaluate new and promising cavity treatments such as SIS structures.

Poster MOPMB017 [3.217 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB017

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 July 2023

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MOPMB021

Correlating Lambda Shift Measurements with RF Performance in Mid-T Heat Treated Cavities

cavity, SRF, niobium, radio-frequency

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

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Received ※ 20 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 15 August 2023

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MOPMB038

Temperature Mapping for Coaxial Cavities at TRIUMF

cavity, SRF, LabView, data-acquisition

183

P. Kolb, T. Junginger, J.J. Keir, R.E. Laxdal, B. Matheson, Z.Y. Yao
TRIUMF, Vancouver, Canada
H. Al Hassini, T. Junginger
UVIC, Victoria, Canada
L. Fearn
UW/Physics, Waterloo, Ontario, Canada

Temperature mapping (T-map) on superconducting radio-frequency (SRF) cavities has been shown as a useful tool to identify defects and other abnormal sources of losses. So far T-map systems have only been realized for elliptical cavities that have an easily accessible outer surface. TEM mode cavities such as quarterwave and halfwave resonators (QWR, HWR) dissipate most of their power on the inner conductor of the coaxial structure. The limited access and constrained space are a challenge for the design of a temperature mapping system. This paper describes the mechanical and electrical design including the data acquisition of a T-map system for the TRIUMF multi-mode coaxial cavities, and first results are shown.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB038

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Received ※ 20 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 30 June 2023

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MOPMB041

Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments

cavity, SRF, niobium, radio-frequency

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 10^10-11(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

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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, radio-frequency

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

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Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 04 July 2023

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MOPMB044

Topographic Evolution of Nitrogen Doped Nb Subjected to Electropolishing

SRF, cavity, niobium, vacuum

207

E.M. Lechner, C.G. Baxley, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
J.W. Angle, M.J. Kelley
Virginia Polytechnic Institute and State University, Blacksburg, USA

Funding: DE-AC05-06OR23177 DE-SC-0014475
Surface quality is paramount in facilitating high perfor-mance SRF cavity operation. Here, we investigate the topographic evolution of samples subjected to N-doping and 600 °C vacuum anneal. We show that in N-doped Nb, niobium nitrides may grow continuously along grain boundaries. Upon electropolishing high slope angle grooves are revealed which sets up a condition that may facilitate a supression of the superheating field.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB044

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Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 17 July 2023

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MOPMB045

Quench Detection in a Superconducting Radio Frequency Cavity with Combined Temperature and Magnetic Field Mapping

cavity, radio-frequency, niobium, SRF

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

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Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 12 August 2023

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MOPMB050

Thermal Feedback in Coaxial SRF Cavities

cavity, niobium, feedback, SRF

224

M.W. McMullin, P. Kolb, R.E. Laxdal, Z.Y. Yao
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada

Funding: Natural Sciences and Engineering Research Council of Canada
The phenomenon of Q-slope in SRF cavities is caused by a combination of thermal feedback and field-dependent surface resistance. There is currently no commonly accepted model of field-dependent surface resistance, and studies of Q-slope generally treat thermal feedback as a correction to whichever surface resistance model is being used. In the present study, we treat thermal feedback as a distinct physical effect whose effect on Q-slope is calculated using a novel finite-element code. We performed direct measurements of liquid helium pool boiling from niobium surfaces to obtain input parameters for the finite-element code. This code was used to analyze data from TRIUMF’s coaxial test cavity program, which has provided a rich dataset of Q-curves at temperatures between 1.7 K and 4.4 K at five different frequencies. Preliminary results show that thermal feedback makes only a small contribution to Q-slope at temperatures near 4.2 K, but has stronger effects as the bath temperature is lowered.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB050

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 09 August 2023

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TUCXA01

Study of the Dynamics of Flux Trapping in Different SRF Materials

experiment, cavity, niobium, controls

380

F. Kramer, S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
T. Kubo
KEK, Ibaraki, Japan

A dedicated experimental setup to measure magnetic flux dynamics and trapped flux in samples is used to precisely map out how trapped flux is influenced by different parameters. The setup allows for rapid thermal cycling of the sample so that effects of cooldown parameters can be investigated in detail. We show how temperature gradient, cooldown rate, and the magnitude of external field influence trapped flux in large grain, fine grain and coated niobium samples. The detailed measurements show unexpected results, namely that too fast cooldowns increase trapped flux, large grain material traps flux only when the external field is larger than a temperature gradient dependent threshold field, and the measured dependence of trapped flux on temperature gradient does not agree with an existing model. Therefore, a new model is presented which agrees better with the measured results.

Slides TUCXA01 [3.180 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCXA01

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Received ※ 17 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 June 2023

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TUPTB002

Modelling Trapped Flux in Niobium

experiment, cavity, niobium, controls

393

F. Kramer, S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
T. Kubo
KEK, Ibaraki, Japan

Detailed measurements of magnetic flux dynamics and trapped magnetic flux in niobium samples were conducted with a new experimental setup that permits precise control of the cooldown parameters. With this setup the dependency of trapped flux on the temperature gradient, external magnetic field, and cooldown rate can be mapped out in more detail compared to cavity measurements. We have obtained unexpected results, and an existing model describing trapped flux in dependence of temperature gradient does not agree with the measured data. Therefore, a new model is developed which describes the magnitude of trapped flux in dependence of the temperature gradient across the sample during cooldown. The model describes the amount of trapped flux lines with help of a density distribution function of the pinning forces of pinning centers and the thermal force which can de-pin flux lines from pinning centers. The model shows good agreement with the measured data and correctly predicts trapped flux at different external flux densities.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB002

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Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 13 July 2023

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TUPTB004

Progress on Zirconium-Doped Niobium Surfaces

niobium, vacuum, electron, superconductivity

398

N. Sitaraman, T. Arias, Z. Baraissov, D.A. Muller
Cornell University, Ithaca, New York, USA
G. Gaitan, M. Liepe, T.E. Oseroff, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the NSF under Award PHY-1549132, the Center for Bright Beams, and in part by CNF (NSF Grant NNCI-2025233), and in part by CCMR (DMR-1719875).
The first experimental studies of zirconium-doped surfaces verified that zirconium can enhance the critical temperature of the surface, resulting in a lower BCS resistance than standard-recipe niobium. However, they also produced a disordered oxide layer, resulting in a higher residual resistance than standard-recipe niobium. Here, we show that zirconium-doped surfaces can grow well-behaved thin oxide layers, with a very thin ternary suboxide capped by a passivating ZrO2 surface. The elimination of niobium pentoxide may allow zirconium-doped surfaces to achieve low residual resistance.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB004

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Received ※ 30 June 2023 — Revised ※ 26 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 22 August 2023

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TUPTB020

Surface Properties and RF Performance of Vapor Diffused Nb₃Sn on Nb after Sequential Anneals below 1000 °C

cavity, SRF, electron, experiment

433

J.K. Tiskumara, J.R. Delayen
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini
JLab, Newport News, Virginia, USA

Nb₃Sn is a next-generation superconducting material that can be used for future superconducting radiofrequency (SRF) accelerator cavities, promising better performance, cost reduction, and higher operating temperature than Nb. The Sn vapor diffusion method is currently the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Among post-coating treatments to optimize the coating quality, higher temperature annealing without Sn is known to degrade Nb₃Sn because of Sn loss. We have investigated Nb₃Sn/Nb samples briefly annealed at 800-1000 °C, for 10 and 20 minutes to potentially improve the surface to enhance the performance of Nb₃Sn-coated cavities. Following the sample studies, a coated single-cell cavity was sequentially annealed at 900 °C and tested its performance each time, improving the cavity’s quality factor relatively. This paper summarizes the sample studies and discusses the RF test results from sequentially annealed SRF Nb₃Sn/Nb cavity.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB020

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Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 01 July 2023 — Issue date ※ 07 July 2023

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TUPTB036

Equidistant Optimization of Elliptical SRF Standing Wave Cavities

cavity, SRF, linac, acceleration

480

V.D. Shemelin
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

A record accelerating rate was achieved earlier in standing wave (SW) SRF cavities when their shape was optimized for lower peak surface magnetic field. In view of new materials with higher limiting magnetic fields, expected for SRF cavities, in the first line Nb₃Sn, the approach to optimization of cavity shape should be revised. A method of equidistant optimization, offered earlier for traveling wave cavities is applied to SW cavities. It is shown here that without limitation by magnetic field, the maximal accelerating rate is defined to a significant degree by the cavity shape. For example, for a cavity with the aperture radius Ra = 35 mm the minimal ratio of the peak surface electric field to the accelerating rate is about Epk/E_acc = 1.54. So, with the maximal surface field experimentally achieved E_pk ¿ 125 MV/m, the maximal achievable accelerating rate is about 80 MeV/m even if there are no restrictions by the magnetic field. Another opportunity ¿ optimization for a low magnetic field, is opening for the same material, Nb₃Sn, with the purpose to have a high quality factor and increased accelerating rate that can be used for industrial linacs.

Poster TUPTB036 [0.787 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUPTB036

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Received ※ 15 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 08 July 2023

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WEPWB048

Geometry Optimization for a Quadrupole Resonator at Jefferson Lab

quadrupole, SRF, simulation, cavity

670

S. Bira, M. Ge, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA
L. Vega Cid, W. Venturini Delsolaro
CERN, Meyrin, Switzerland

Funding: This manuscript is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-6OR23177 with Jefferson Science Associates
The quadrupole resonator (QPR) is a sample characterization tool to measure the RF properties of superconducting materials using the calorimetry method at different temperatures, magnetic fields, and frequencies. Such resonators are currently operating at CERN and HZB but suffer from Lorentz force detuning and modes overlapping, resulting in higher uncertainties in surface resistance measurement. Using the two CERN’s QPR model iterations, the geometry was optimized via electromagnetic and mechanical simulations to eliminate these issues. The new QPR version was modeled for an increasing range of magnetic fields. The magnetic field is concentrated at the center of the sample to reduce the uncertainty in surface resistance measurements significantly. This paper will discuss the QPR geometry optimization for the new version of QPR, which is now progressing towards fabrication.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB048

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Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 19 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

cavity, niobium, SRF, electron

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 WEPWB116 [1.312 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB116

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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

cavity, cryomodule, niobium, SRF

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

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Received ※ 15 June 2023 — Revised ※ 28 June 2023 — Accepted ※ 03 July 2023 — Issue date ※ 13 July 2023

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WEPWB128

Experimental Study of Mechanical Dampers for the FRIB β=0.041 Quarter-Wave Resonators

cavity, damping, operation, linac

898

J. Brown, W. Chang, W. Hartung, S.H. Kim, T. Xu
FRIB, East Lansing, Michigan, USA

Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award numbers DE-SC0018362 and DE-SC0000661 and Michigan State University.
The ’pendulum’ mechanical mode of quarter-wave resonators (QWR) often causes an issue with microphonics and/or ponderomotive instability unless otherwise the inner conductors are properly stiffened and/or damped. FRIB QWRs are equipped with a Legnaro-style frictional damper installed inside of the inner conductor such that it counteracts the oscillations of the inner conductor. In cryomodule tests and linac operation, we observed that the damping efficiency is different for a few β=0.041 QWRs. This study aimed to experimentally characterize the damping efficacy as a function of damper mass and surface roughness. We present damping measurements at room temperature and at two different masses and surface roughness as well as discuss future studies for damper re-optimization based on this follow-on study.

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB128

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Received ※ 20 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 04 August 2023

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WEPWB133

Testing of the 2.6 GHz SRF Cavity Tuner for the Dark Photon Experiment at 2 K

cavity, photon, SRF, experiment

907

C. Contreras-Martinez, B. Giaccone, I.V. Gonin, T.N. Khabiboulline, O.S. Melnychuk, Y.M. Pischalnikov, S. Posen, O.V. Pronitchev, J.C. Yun
Fermilab, Batavia, Illinois, USA

At FNAL two 2.6 GHz SRF cavities are being used to search for dark photons, the experiment can be conducted at 2 K or in a dilution refrigerator. Precise frequency tuning is required for these two cavities so they can be matched in frequency. A cooling capacity constraint on the dilution refrigerator only allows piezo actuators to be part of the design of the 2.6 GHz cavity tuner. The tuner is equipped with three encapsulated piezo that deliver the long- and short-range frequency tuning. Modifications were implemented on the first tuner design due to the low forces on the piezos due to the cavity. Three brass rods with Belleville washers were added to the design to increase the overall force on the piezos. The results at 2 K of testing this tuner with and without the modification will be presented.

Poster WEPWB133 [0.829 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB133

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Received ※ 16 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 04 July 2023

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