Fundamental SRF research and development
High quality factors/high gradients
Paper Title Page
MOPMB020 A Comprehensive Picture of Hydride Formation and Dissipation 119
 
  • N. Sitaraman, T. Arias
    Cornell University, Ithaca, New York, USA
  • A.V. Harbick, M.K. Transtrum
    Brigham Young University, Provo, USA
  • M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Re­search link­ing sur­face hy­drides to Q-dis­ease, and the sub­se­quent de­vel­op­ment of meth­ods to elim­i­nate sur­face hy­drides, is one of the great suc­cesses of SRF cav­ity R\&D. We use time-de­pen­dent Ginzburg-Lan­dau to ex­tend the the­ory of hy­dride dis­si­pa­tion to sub-sur­face hy­drides. Just as sur­face hy­drides cause Q-dis­ease be­hav­ior, we show that sub-sur­face hy­drides cause high-field Q-slope (HFQS) be­hav­ior. We find that the abrupt onset of HFQS is due to a tran­si­tion from a vor­tex-free state to a vor­tex-pen­e­tra­tion state. We show that con­trol­ling hy­dride size and depth through im­pu­rity dop­ing can elim­i­nate HFQS. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB020  
About • Received ※ 30 June 2023 — Revised ※ 18 July 2023 — Accepted ※ 19 August 2023 — Issue date ※ 19 August 2023
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MOPMB022 Recent mid-T Single-Cell Treatments R&D at DESY 129
 
  • C. Bate, D. Reschke, J. Schaffran, L. Steder, L. Trelle, H. Weise
    DESY, Hamburg, Germany
  
  The chal­lenge of im­prov­ing the per­for­mance of SRF cav­i­ties is being faced world­wide. One ap­proach is to mod­ify the su­per­con­duct­ing sur­face prop­er­ties through cer­tain bak­ing pro­ce­dures. Re­cently a nio­bium re­tort fur­nace placed di­rectly under an ISO4 clean room has been re­fur­bished at DESY. Thanks to an in­ter-vac­uum cham­ber and cry­op­umps, with high pu­rity val­ues in the mass spec­trum it is work­ing in the UHV range of 2·10-8 mbar. The medium tem­per­a­ture (mid-T) heat treat­ments around 300°C are promis­ing and suc­cess­fully de­liver re­pro­ducible very high Q₀ val­ues of 2-5·1010 at medium field strengths of 16 MV/m. Since the first DESY and ZRI mid-T cam­paign yielded promis­ing re­sults, fur­ther re­sults of 1.3 GHz sin­gle-cell cav­i­ties are pre­sented here after sev­eral mod­i­fied treat­ments of the mid-T recipe. In ad­di­tion, sam­ples were added to each treat­ment, the RRR value change was ex­am­ined, and sur­face analy­ses were sub­se­quently per­formed. The main focus of the sam­ple study is the pre­cise role of the changes in the con­cen­tra­tion of im­pu­ri­ties on the sur­face. In par­tic­u­lar, the change in oxy­gen con­tent due to dif­fu­sion processes is sus­pected to be the cause of en­hanc­ing the per­for­mance.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB022  
About • Received ※ 18 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 01 July 2023
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MOPMB023 Magnetic Flux Expulsion in TRIUMF’s Multi-Mode Coaxial Cavities 135
SUSPB011   use link to see paper's listing under its alternate paper code  
 
  • R.R. Gregory, T. Junginger, M.W. McMullin
    UVIC, Victoria, Canada
  • T. Junginger, P. Kolb, R.E. Laxdal, M.W. McMullin, Z.Y. Yao
    TRIUMF, Vancouver, Canada
  
  The ex­ter­nal mag­netic flux sen­si­tiv­ity of SRF cav­i­ties is an im­por­tant char­ac­ter­is­tic of SRF ac­cel­er­a­tor de­sign. Pre­vi­ous stud­ies have shown that n-doped el­lip­ti­cal cav­i­ties are very sen­si­tive to ex­ter­nal fields, re­sult­ing in strin­gent re­quire­ments for resid­ual field and cav­ity cool-down speed. Few such stud­ies have been done on HWRs and QWRs. The im­pact of ap­plied field di­rec­tion and cool-down speed of flux ex­pul­sion for these cav­i­ties is poorly un­der­stood. This study ex­plores the ef­fect of these cool-down char­ac­ter­is­tics on TRI­UMF¿s QWR using COM­SOL ® sim­u­la­tions and ex­per­i­men­tal re­sults. This study seeks to max­i­mize the flux ex­pul­sion that oc­curs when a cav­ity is cooled down through its su­per­con­duct­ing tem­per­a­ture. Flux ex­pul­sion is af­fected by the cool-down speed, tem­per­a­ture gra­di­ent, and ori­en­ta­tion of the cav­ity rel­a­tive to an ap­plied mag­netic field. It was found that for a ver­ti­cally ap­plied mag­netic field the cool-down speed and tem­per­a­ture gra­di­ent did not have a sig­nif­i­cant ef­fect on flux ex­pul­sion. Con­trar­ily, a hor­i­zon­tal mag­netic field can be nearly com­pletely ex­pelled by a fast, high tem­per­a­ture gra­di­ent cool-down.  
poster icon Poster MOPMB023 [2.191 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB023  
About • Received ※ 17 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 30 July 2023
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MOPMB024 Flux Expulsion Studies of Niobium Material of 650 MHz Cavities for PIP-II 141
TUPTB003   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB026 Development of Transformative Cavity Processing - Superiority of Electropolishing on High Gradient Performance over Buffered Chemical Polishing at Low Frequency (322 MHz) 145
 
  • K. Saito, C. Compton, K. Elliott, W. Hartung, S.H. Kim, T.K. Konomi, E.S. Metzgar, S.J. Miller, L. Popielarski, A.T. Taylor, T. Xu
    FRIB, East Lansing, Michigan, USA
  
  Funding: The work is supported by DOE Awards DE-SC0022994.
A DOE grant R&D ti­tled ¿De­vel­op­ment of Trans­for­ma­tive Prepa­ra­tion Tech­nol­ogy to Push up High Q/G Per­for­mance of FRIB Spare HWR Cry­omod­ule Cav­i­ties¿ is on­go­ing at FRIB. This R&D is for 2 years since Sep­tem­ber 2022. This pro­ject pro­poses four ob­jec­tives: 1) Su­pe­ri­or­ity on high gra­di­ent per­for­mance of elec­trop­o­l­ish­ing (EP) over buffered chem­i­cal pol­ish­ing at low fre­quency (322 MHz), 2) High Qo per­for­mance by the local mag­netic shield, 3) De­vel­op­ment of HFQS-free BCP and, 4) Wet N-dop­ing method. This paper will re­port the re­sult of first ob­ject, and a local mag­netic shield de­sign and sim­u­la­tion to re­duce the resid­ual mag­netic field < 0.1 mG in the ver­ti­cal test Dewar, for the ob­ject 2. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB026  
About • Received ※ 14 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 08 July 2023
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MOPMB027 Successful Superheating Field Formulas from an Intuitive Model 151
 
  • K. Saito, T. Konomi
    FRIB, East Lansing, Michigan, USA
  
  Funding: Work supported by the U.S. Department of Energy Office of Science DE-S0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511
To date, many the­o­ret­i­cal for­mu­las for su­per­heat­ing field on SRF cav­ity are al­ready pro­posed based rather com­pli­cated cal­cu­la­tions. This paper pro­poses the for­mu­las by a very in­tu­itive sim­ple model: en­ergy bal­ance be­tween RF mag­netic en­ergy and su­per­con­duct­ing con­densed one, and a con­di­tion of van­ish­ing the mir­ror vor­tex line image. The pen­e­tra­tion of a sin­gle vor­tex de­ter­mines the su­per­heat­ing field for a type II su­per­con­duc­tor. On the other hand, for type I su­per­con­duc­tors, the sur­face flux pen­e­tra­tion de­ter­mines it. The for­mula fits very well quan­ti­ta­tively the re­sults of nio­bium cav­ity and Nb₃Sn one. In ad­di­tion, it gives a nice guide­line for new ma­te­r­ial be­yond nio­bium.
male, senior 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB027  
About • Received ※ 23 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 15 July 2023
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MOPMB029 Exploring the Dynamics of Transverse Inter-Planar Coupling in the Superconducting Section of the PIP-II Linac 155
 
  • A. Pathak
    Fermilab, Batavia, Illinois, USA
  • E. Pozdeyev
    JLab, Newport News, USA
  
  This study in­ves­ti­gates the cru­cial role that an ac­cu­rate un­der­stand­ing of in­ter-pla­nar cou­pling in the trans­verse plane plays in reg­u­lat­ing charged par­ti­cle dy­nam­ics in a high-in­ten­sity lin­ear ac­cel­er­a­tor and min­i­miz­ing foil/sep­tum im­pacts dur­ing in­jec­tion from the linac to a ring. We in-depth an­a­lyze the emer­gence and evo­lu­tion of trans­verse in­ter-pla­nar cou­pling through mul­ti­ple ac­tive lat­tice el­e­ments, tak­ing into ac­count space charge and field non­lin­ear­i­ties in the su­per­con­duct­ing sec­tion of the PIP-II linac. The ar­ti­cle com­pares var­i­ous an­a­lyt­i­cal, nu­mer­i­cal, and ex­per­i­men­tal tech­niques for mea­sur­ing trans­verse cou­pling using beam and lat­tice ma­tri­ces and pro­vides in­sight into ef­fec­tive strate­gies for its mit­i­ga­tion prior to ring in­jec­tio  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB029  
About • Received ※ 21 June 2023 — Revised ※ 24 June 2023 — Accepted ※ 27 June 2023 — Issue date ※ 05 July 2023
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MOPMB030 Medium Temperature Furnace Baking of Low-beta 650 MHz Five-cell Cavities 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 162
SUSPB012   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB033 Efforts to Suppress Field Emission in SRF Cavities at KEK 167
 
  • M. Omet, H. Araki, T. Dohmae, H. Ito, R. Katayama, K. Umemori, Y. Yamamoto
    KEK, Ibaraki, Japan
  
  Our main ob­jec­tive is to achieve as high as pos­si­ble qual­ity fac­tors Q₀ and max­i­mal ac­cel­er­at­ing volt­ages Eacc within 1.3 GHz su­per­con­duct­ing radio fre­quency (SRF) cav­i­ties. Be­side an ad­e­quate sur­face treat­ment, key to achieve good per­for­mance is a proper as­sem­bly in the clean room prior cav­ity test­ing or op­er­a­tion. In this con­tri­bu­tion we pre­sent the meth­ods and re­sults of our ef­forts to get a bet­ter un­der­stand­ing of our clean room en­vi­ron­ment and the par­tic­u­late gen­er­a­tion caused dur­ing the as­sem­bly work. Fur­ther­more, we pre­sent the mea­sures taken to sup­press filed emis­sion, fol­lowed by an analy­sis of ver­ti­cal test re­sults of the last six years.  
poster icon Poster MOPMB033 [1.532 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-MOPMB033  
About • Received ※ 14 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 02 September 2023 — Issue date ※ 02 September 2023
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MOPMB036 Magnetic Field Mapping of a Large-Grain 1.3 GHz Single-Cell Cavity 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 178
SUSPB013   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB038 Temperature Mapping for Coaxial Cavities at TRIUMF 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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MOPMB040 Comparing the Effectiveness of Low Temperature Bake in EP and BCP Cavities 187
SUSPB014   use link to see paper's listing under its alternate paper code  
 
  • 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
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPMB041 Microstructure Development in a Cold Worked SRF Niobium Sheet After Heat Treatments 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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MOPMB043 Characterization of Dissipative Regions of an N-Doped SRF Cavity 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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MOPMB044 Topographic Evolution of Nitrogen Doped Nb Subjected to Electropolishing 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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MOPMB050 Thermal Feedback in Coaxial SRF Cavities 224
SUSPB020   use link to see paper's listing under its alternate paper code  
 
  • 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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MOPMB076 Surface Characterization Studies of Gold-Plated Niobium 290
SUSPB024   use link to see paper's listing under its alternate paper code  
 
  • 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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TUIBA01 A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities 361
 
  • M.M. Kelley, T. Arias, S. Deyo, D. Liarte, J.P. Sethna, N. Sitaraman
    Cornell University, Ithaca, New York, USA
  • M. Liepe, T.E. Oseroff
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Ex­per­i­ments on su­per­con­duct­ing cav­i­ties have found that under large RF fields the qual­ity fac­tor can im­prove with in­creas­ing field am­pli­tude, a so-called anti-Q slope. We nu­mer­i­cally solve the Bo­goli­ubov-de Gennes equa­tions at a su­per­con­duct­ing sur­face in a par­al­lel mag­netic field, find­ing at large fields there are sur­face qua­si­par­ti­cle states with en­er­gies below the bulk su­per­con­duct­ing gap that emerge and dis­ap­pear as the field cy­cles. Mod­i­fy­ing the stan­dard two-fluid model, we in­tro­duce a ‘‘three’’-fluid model where we par­ti­tion the nor­mal fluid to con­sider con­tin­uum and sur­face qua­si­par­ti­cle states sep­a­rately. We com­pute dis­si­pa­tion in a semi-clas­si­cal the­ory of con­duc­tiv­ity, where we pro­vide phys­i­cal es­ti­mates of elas­tic scat­ter­ing times of Bo­goli­ubov qua­si­par­ti­cles with point-like im­pu­ri­ties hav­ing po­ten­tial strengths in­formed from com­ple­men­tary ab ini­tio cal­cu­la­tions of im­pu­ri­ties in bulk nio­bium. We show, in this sim­ple yet ef­fec­tive frame­work, how the rel­a­tive scat­ter­ing rates of sur­face and con­tin­uum qua­si­par­ti­cle states can play a role in pro­duc­ing an anti-Q slope while demon­strat­ing how this model nat­u­rally in­cludes a mech­a­nism for turn­ing the anti-Q slope on and off.
S. Deyo, M. Kelley et al. Phys. Rev. B 106, 104502 (2022) 		 
slides icon Slides TUIBA01 [2.019 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUIBA01  
About • Received ※ 19 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 28 June 2023 — Issue date ※ 08 July 2023
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TUIBA02
 Vacancy Dynamics in Niobium and Its Native Oxides and Their Potential Implications for Quantum Computing and Superconducting Accelerators  
 
  • M. Wenskat
    DESY, Hamburg, Germany
  
  Funding: This work was supported by the BMBF under the research grants 05K19GUB and 05H2021.
In re­cent years, su­per­con­duct­ing ra­dio-fre­quency (SRF) cav­i­ties have been con­sid­ered as can­di­dates for qubits in quan­tum com­put­ing, show­ing longer pho­ton life­times and, there­fore, longer de­co­her­ence times of a cav­ity stored qubit com­pared to many other re­al­iza­tions. In mod­ern par­ti­cle ac­cel­er­a­tors, SRF cav­i­ties are the work­horse. Con­tin­u­ous re­search and de­vel­op­ment ef­forts are being un­der­taken to im­prove their prop­er­ties, i.e., to in­crease the ac­cel­er­at­ing field and lower the sur­face re­sis­tance, which in turn in­crease the en­ergy reach and duty cycle of ac­cel­er­a­tors. While some ex­per­i­men­tal mile­stones have been achieved, the mech­a­nisms be­hind the still ob­served losses re­main not fully un­der­stood. This talk will show that a re­cently re­ported tem­per­a­ture treat­ment of Nb SRF cav­i­ties in the tem­per­a­ture range of 573-673 K, which re­duces the resid­ual sur­face re­sis­tance to un­prece­dented val­ues, is linked to a re­or­ga­ni­za­tion of the nio­bium oxide and near-sur­face va­cancy struc­ture and that this re­or­ga­ni­za­tion can ex­plain the ob­served im­proved per­for­mance in both ap­pli­ca­tions, quan­tum com­put­ing and SRF cav­i­ties. 		 
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TUCBA01 Measurements of the Amplitude-Dependent Microwave Surface Resistance of a Proximity-Coupled Au/Nb Bilayer 369
 
  • T.E. Oseroff, M. Liepe, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  A sam­ple host cav­ity is used to mea­sure the sur­face re­sis­tance of a nio­bium sub­strate with a gold film de­posited in place of its sur­face oxide. This talk will re­port about this mea­sure­ment re­sult. The film thick­ness of the gold layer was in­creased from 0.1 nm to 2.0 nm in five steps to study the im­pact of the nor­mal layer thick­ness. The 0.1 nm film was found to re­duce the sur­face re­sis­tance below its value with the sur­face oxide pre­sent and to en­hance the quench field. The mag­ni­tude of the sur­face re­sis­tance in­creased sub­stan­tially with gold film thick­ness. The sur­face re­sis­tance field-de­pen­dence ap­peared to be in­de­pen­dent from the nor­mal layer thick­ness. The ob­ser­va­tions re­ported in this work have pro­found im­pli­ca­tions for both low-field and high-field S.C. mi­crowave de­vices. By con­trol­ling or elim­i­nat­ing the nio­bium oxide using a gold layer to pas­si­vate the nio­bium sur­face, it may be pos­si­ble to im­prove the per­for­mance of SRF cav­i­ties used for par­ti­cle ac­cel­er­a­tion. This method to re­duce sur­face ox­i­da­tion while main­tain­ing low sur­face re­sis­tance could also be rel­e­vant for min­i­miz­ing dis­si­pa­tion due to two-level sys­tems ob­served in low-field low-tem­per­a­ture de­vices.  
slides icon Slides TUCBA01 [2.292 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-TUCBA01  
About • Received ※ 19 June 2023 — Revised ※ 29 June 2023 — Accepted ※ 30 June 2023 — Issue date ※ 26 July 2023
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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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TUCXA01 Study of the Dynamics of Flux Trapping in Different SRF Materials 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 icon 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 393
SUSPB017   use link to see paper's listing under its alternate paper code  
 
  • 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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WEIAA01
 The Frequency Shift and Q of Disordered Superconducting RF Cavities  
 
  • H. Ueki, J.A. Sauls, M. Zarea
    LSU, Baton Rouge, USA
  
  Funding: U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract No. DE-AC02-07CH11359.
Su­per­con­duct­ing RF (SRF) cav­ity res­onators with ul­tra­high-Q, orig­i­nally de­vel­oped for par­ti­cle ac­cel­er­a­tor tech­nol­ogy, are a key tech­nol­ogy plat­form for de­tec­tors of rare events, e.g. light by light scat­ter­ing me­di­ated by vir­tual elec­tron-positron pairs, ax­ions [1] and high-fre­quency grav­i­ta­tional waves [2]. The mech­a­nism(s) lead­ing to cur­rent lim­its in Q are not fully un­der­stood. We de­vel­oped a nu­mer­i­cal method to cal­cu­late Q and cav­ity res­o­nant fre­quency shifts based on non­equi­lib­rium the­ory of su­per­con­duc­tiv­ity, in­clud­ing the role of im­pu­rity dis­or­der, com­bined with Slater’s method for solv­ing Maxwell’s equa­tions for the EM field con­fined in a cav­ity [3]. Our re­sults for the fre­quency shift and Q are in ex­cel­lent agree­ment with ex­per­i­men­tal data re­ported by the SRF group at Fer­mi­lab [4]. As a mea­sure of the pre­dic­tive ca­pa­bil­ity of the the­ory we are able to quan­ti­ta­tively ac­count for changes in the res­o­nant fre­quency of order 10 Hz for GHz SRF cav­i­ties over tem­per­a­ture ranges of 0.001 Tc. This level of pre­dic­tive the­ory is es­sen­tial for fur­ther im­prove­ments in per­for­mance of su­per­con­duct­ing res­onators and de­vices for quan­tum sens­ing and quan­tum proces­sors.
[1] Z. Bogorad et al., Phys. Rev. Lett. 123, 021801 (2019).
[2] A. Berlin et al., arXiv:2303.0151.
[3] H. Ueki, M. Zarea, and J. A. Sauls, arXiv:2207.14236.
[4] D. Bafia et al., arXiv:2103.10601. 		 
slides icon Slides WEIAA01 [4.722 MB]  
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WEIAA02
 Temperature Responses of Superconducting Niobium Properties in Experiment and Simulation  
 
  • Z.T. Yang, J.K. Hao, H. Liu, K.X. Liu, S.W. Quan
    PKU, Beijing, People’s Republic of China
  
  Mild, medium, and high tem­per­a­ture bak­ing has been re­searched to ob­tain high-Q₀ SRF nio­bium cav­i­ties in past decades. It sug­gests that nio­bium has dif­fer­ent prop­er­ties when treated at dif­fer­ent tem­per­a­tures. We con­ducted var­i­ous ex­per­i­ments on SRF-cav­ity-class nio­bium sam­ples, and the sys­tem­atic mea­sure­ments in­cluded not only im­pu­rity analy­sis via TOF-SIMS, in-situ XPS, in-situ ESEM, HRTEM, but also su­per­con­duc­tor mea­sure­ments via in-situ ARPES. We also per­formed quan­ti­ta­tive atomic sim­u­la­tion of the im­pu­ri­ties in nio­bium bulks at zero tem­per­a­ture, and found in­ter­sti­tial car­bon had sim­i­lar trap­ping ef­fect on in­ter­sti­tial hy­dro­gen as in­ter­sti­tial ni­tro­gen and oxy­gen did. We found the mildly in­creased in­ter­sti­tial car­bons and oxy­gens dur­ing medium tem­per­a­ture bak­ing not only sup­pressed the hy­dro­gen ac­cu­mu­la­tion and hy­dride pre­cip­i­ta­tion dur­ing cool­ing down, but also re­duced the elec­tron mean free path to the op­ti­mal range which yielded de­clined BCS re­sis­tance. There­fore, the sur­face re­sis­tances of the cav­i­ties were re­duced and the Q₀ val­ues were im­proved cor­re­spond­ingly.  
slides icon Slides WEIAA02 [15.615 MB]  
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WEPWB044 Realization of Accelerating Gradient Larger than 25 MV/m on High-Q 1.3 GHz 9-Cell Cavities for SHINE 658
SUSPB039   use link to see paper's listing under its alternate paper code  
 
  • Y. Zong, Q.X. Chen, X. Huang, Z. Wang
    SINAP, Shanghai, People’s Republic of China
  • J.F. Chen, P.C. Dong, H.T. Hou, X.Y. Pu, J. Shi, S. Sun, D. Wang, J.N. Wu, S. Xing, S.J. Zhao, Y.L. Zhao
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  • Y.W. Huang
    ShanghaiTech University, Shanghai, People’s Republic of China
  • X.W. Wu
    Zhangjiang Lab, Shanghai, People’s Republic of China
  
  Funding: This work was supported by Shanghai Municipal Science and Technology Major Project (No. 2017SHZDZX02).
We pre­sent our stud­ies on the op­ti­mized ni­tro­gen-dop­ing and medium-tem­per­a­ture bak­ing recipes ap­plied on 1.3GHz SRF cav­i­ties, aim­ing at meet­ing the re­quire­ments of the SHINE pro­ject. The op­ti­mized ni­tro­gen-dop­ing process re­sulted in achiev­ing a Q₀ of over 4.0×1010 at medium field and a max­i­mum ac­cel­er­at­ing gra­di­ent ex­ceed­ing 35 MV/m on sin­gle cell cav­i­ties, and a Q₀ of over 2.8×1010 at medium field and a max­i­mum ac­cel­er­at­ing gra­di­ent ex­ceed­ing 26 MV/m in 9-cell cav­i­ties. For 1.3 GHz 9-cell cav­i­ties sub­jected to medium-tem­per­a­ture bak­ing, Q₀ val­ues ex­ceed­ing 3.5×1010 at 16 MV/m and max­i­mum ac­cel­er­at­ing gra­di­ents sur­pass­ing 25 MV/m were achieved. These stud­ies pro­vide two op­tions of high-Q recipes for SHINE cav­i­ties. The treat­ment processes of cav­i­ties and their ver­ti­cal test re­sults are de­scribed in this paper.
*chenjinfang@sari.ac.cn
 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB044  
About • Received ※ 19 June 2023 — Revised ※ 22 June 2023 — Accepted ※ 26 June 2023 — Issue date ※ 26 June 2023
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WEPWB045 The Oxidizing Responses of Baked Niobium Exposed to Various Gases via In-situ NAXPS 662
SUSPB040   use link to see paper's listing under its alternate paper code  
 
  • Z.T. Yang, J.K. Hao, K.X. Liu, S.W. Quan
    PKU, Beijing, People’s Republic of China
  
  We car­ried out in-situ NAXPS (Near-at­mos­pheric X-ray Pho­to­elec­tron Spec­troscopy) on SRF-cav­ity class nio­bium to ob­serve its ox­i­diz­ing re­sponses when ex­posed to var­i­ous gases. The nio­bium sam­ples were baked at 800°C until the peaks of nio­bium ox­ides dis­ap­peared in the spec­trum. Then the re­vealed pure nio­bium sam­ples were ex­posed to the air-pro­por­tion mix­ture of ni­tro­gen and oxy­gen, pure oxy­gen, and pure water vapor re­spec­tively. And for the pure oxy­gen and water vapor group, we also car­ried out TOF-SIMS (Time-of-Flight Sec­ondary Ion Mass Spec­troscopy) mea­sure­ments be­fore and after the bak­ing and ox­i­da­tion ex­per­i­ments. We found that pure oxy­gen and water vapor could ox­i­dize nio­bium at sim­i­lar rate which was faster than the N2/O2 mix­ture. After re-ox­i­dized by pure oxy­gen and water vapor, the nio­bium sam­ple pre­sented a sig­nif­i­cant in­crease of in­ter­sti­tial car­bon and a mod­er­ate in­crease of in­ter­sti­tial oxy­gen in the mag­netic pen­e­tra­tion depth, while it showed a mild de­crease of in­ter­sti­tial hy­dro­gen.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB045  
About • Received ※ 15 June 2023 — Revised ※ 23 June 2023 — Accepted ※ 25 June 2023 — Issue date ※ 31 July 2023
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WEPWB084 The Interaction among Interstitial C/N/O/H and Vacancy in Niobium via First-Principles Calculation 778
 
  • H. Liu, J.K. Hao, Z.T. Yang
    PKU, Beijing, People’s Republic of China
  
  We cal­cu­late the in­ter­ac­tion among zero di­men­sional de­fects in nio­bium lat­tice through first-prin­ci­ples cal­cu­la­tion. And we com­pare the trap­ping ef­fect of hy­dro­gen among car­bon, ni­tro­gen, and oxy­gen as well as the trap­ping ef­fect of in­ter­sti­tial atoms by va­cancy. We find that the in­ter­sti­tial C/N/O have sim­i­lar ef­fect of trap­ping in­ter­sti­tial hy­dro­gen in nio­bium lat­tice, and the va­cancy can trap in­ter­sti­tial C/N/O/H in ad­ja­cent pro­to­cells and strengthen their chem­i­cal bond with Nb. These cal­cu­la­tions give some ex­pla­na­tion for im­prov­ing su­per­con­duct­ing per­for­mance of nio­bium cav­i­ties through medium tem­per­a­ture bak­ing.  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2023-WEPWB084  
About • Received ※ 15 June 2023 — Revised ※ 25 June 2023 — Accepted ※ 29 June 2023 — Issue date ※ 03 July 2023
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