Keyword: niobium
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TUOXSP2 Analysis of Low RRR SRF Cavities cavity, SRF, accelerating-gradient, radio-frequency 783
 
  • 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. This work was supported by the University of Chicago.
Re­cent find­ings in the su­per­con­duct­ing ra­dio-fre­quency (SRF) com­mu­nity have shown that in­tro­duc­ing cer­tain im­pu­ri­ties into high-pu­rity nio­bium can im­prove qual­ity fac­tors and ac­cel­er­at­ing gra­di­ents. Suc­cess has been found in ni­tro­gen-dop­ing, dif­fu­sion of the na­tive oxide into the nio­bium sur­face, and thin films of al­ter­nate su­per­con­duc­tors atop a nio­bium bulk cav­ity. 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 with a low resid­ual re­sis­tance ratio (RRR) and cor­re­late these im­pu­ri­ties with the RF per­for­mance of low RRR cav­i­ties so that the mech­a­nism of re­cent im­pu­rity-based im­prove­ments can be bet­ter un­der­stood and im­proved upon. Ad­di­tion­ally, we per­form a low tem­per­a­ture bake on the low RRR cav­ity to eval­u­ate how the in­ten­tional ad­di­tion of oxy­gen to the RF layer af­fects per­for­mance. We have found that low RRR cav­i­ties ex­pe­ri­ence low tem­per­a­ture-de­pen­dent BCS re­sis­tance be­hav­ior more promi­nently than their high RRR coun­ter­parts. The re­sults of this study have the po­ten­tial to un­lock a new un­der­stand­ing on SRF ma­te­ri­als. 		 
slides icon Slides TUOXSP2 [1.495 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUOXSP2  
About • Received ※ 08 June 2022 — Accepted ※ 11 June 2022 — Issue date ※ 25 June 2022  
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TUPOTK005 Mitigation of Parasitic Losses in the Quadrupole Resonator Enabling Direct Measurements of Low Residual Resistances of SRF Samples quadrupole, SRF, cavity, simulation 1196
 
  • S. Keckert, R. Kleindienst, J. Knobloch, F. Kramer, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • W. Ackermann, H. De Gersem
    TEMF, TU Darmstadt, Darmstadt, Germany
  • X. Jiang, A.O. Sezgin, M. Vogel
    University Siegen, Siegen, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
  • M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  The quadru­pole res­onator (QPR) is a ded­i­cated sam­ple-test cav­ity for the RF char­ac­ter­i­za­tion of su­per­con­duct­ing sam­ples in a wide tem­per­a­ture, RF field and fre­quency range. Its main pur­pose are high res­o­lu­tion mea­sure­ments of the sur­face re­sis­tance with di­rect ac­cess to the resid­ual re­sis­tance thanks to the low fre­quency of the first op­er­at­ing quadru­pole mode. Be­sides the well-known high res­o­lu­tion of the QPR, a bias of mea­sure­ment data to­wards higher val­ues has been ob­served, es­pe­cially at higher har­monic quadru­pole modes. Nu­mer­i­cal stud­ies show that this can be ex­plained by par­a­sitic RF losses on the adapter flange used to mount sam­ples into the QPR. Coat­ing sev­eral mi­crom­e­ter of nio­bium on those sur­faces of the stain­less steel flange that are ex­posed to the RF fields sig­nif­i­cantly re­duced this bias, en­abling a di­rect mea­sure­ment of a resid­ual re­sis­tance smaller than 5 nano-Ohm at 2 K and 413 MHz.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK005  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 28 June 2022
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TUPOTK006 Systematic Investigation of Flux Trapping Dynamics in Niobium Samples cavity, experiment, SRF, controls 1200
 
  • F. Kramer, S. Keckert, S. Keckert, J. Knobloch, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  • J. Knobloch, O. Kugeler
    BESSY GmbH, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
  
  Trapped mag­netic flux in su­per­con­duct­ing cav­i­ties can sig­nif­i­cantly in­crease sur­face re­sis­tance, and, thereby, lim­its the cav­i­ties’ per­for­mance. To re­duce trapped flux in cav­i­ties, a bet­ter un­der­stand­ing of the fun­da­men­tal mech­a­nism of flux trap­ping is vital. We de­velop a new ex­per­i­men­tal de­sign: mea­sur­ing mag­netic flux den­sity at 15 points just above a nio­bium sheet of di­men­sions (100 x 60 x 3) mm with a time res­o­lu­tion of up to 2 ms and a flux res­o­lu­tion bet­ter than 0.5 µT. This setup al­lows us to con­trol the tem­per­a­ture gra­di­ent and cooldown rate, both in­de­pen­dently of each other, as well as the mag­ni­tude and di­rec­tion of an ex­ter­nal mag­netic field. We pre­sent data gath­ered on a large-grain sam­ple as well as on a fine-grain sam­ple. Our data sug­gests that not only the tem­per­a­ture gra­di­ent but also the cooldown rate af­fects trapped flux. Ad­di­tion­ally, we de­tect a non-triv­ial re­la­tion­ship be­tween trapped flux and mag­ni­tude of ap­plied field.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK006  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022
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TUPOTK008 Cavity Designs for the Ch3 to Ch11 and Bellow Tuner Investigation of the Superconducting Heavy Ion Accelerator Heliac cavity, SRF, heavy-ion, simulation 1204
 
  • T. Conrad, M. Busch, H. Podlech, M. Schwarz
    IAP, Frankfurt am Main, Germany
  • K. Aulenbacher
    IKP, Mainz, Germany
  • K. Aulenbacher, W.A. Barth, F.D. Dziuba, V. Gettmann, T. Kürzeder, S. Lauber, J. List, M. Miski-Oglu
    HIM, Mainz, Germany
  • W.A. Barth, M. Basten, F.D. Dziuba, M. Heilmann, A. Rubin, A. Schnase, S. Yaramyshev
    GSI, Darmstadt, Germany
  
  New CH-DTL cav­i­ties de­signs of the planned Helmholtz Lin­ear Ac­cel­er­a­tor (HE­LIAC) are de­vel­oped in col­lab­o­ra­tion of HIM, GSI and IAP Frank­furt. The linac, op­er­ated in cw-mode with a final en­ergy of 7.3 MeV/u, is in­tended for var­i­ous ex­per­i­ments, in par­tic­u­lar with heavy ions at en­er­gies close to the Coulomb bar­rier for re­search on SHE. Twelve sc CH cav­i­ties are fore­seen, di­vided into four dif­fer­ent cryostats. Each cav­ity will be equipped with dy­namic bel­low tuner. After suc­cess­ful beam tests with CH0, CH3 to CH11 are being de­signed. Based on the ex­pe­ri­ence gained so far, op­ti­miza­tion will be made, which will lead to both an in­crease in per­for­mance in terms of re­duc­ing the peak fields lim­it­ing su­per­con­duc­tiv­ity and a re­duc­tion in man­u­fac­tur­ing costs and time. In order to op­ti­mize man­u­fac­tur­ing, at­ten­tion was paid to de­sign many parts of the cav­ity, such as lids, spokes, tuner and he­lium shell, with the same geo­met­ri­cal di­men­sions. In ad­di­tion, a tuner test rig was de­vel­oped, which will be used to in­ves­ti­gate the me­chan­i­cal prop­er­ties of the bel­low tuner. For this pur­pose, dif­fer­ent sim­u­la­tions were made in order to re­al­ize con­di­tions as close as pos­si­ble to re­al­ity in the test rig.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK008  
About • Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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TUPOTK010 Nitric Acid Soaking after Imperfect Furnace Treatments cavity, SRF, radio-frequency, linac 1211
 
  • R. Ghanbari, A. Dangwal Pandey
    DESY, Hamburg, Germany
  • C. Bate
    University of Hamburg, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  An­neal­ings of nio­bium cav­i­ties in UHV or ni­tro­gen at­mos­pheres are cru­cial for the per­for­mance in the later cryo­genic tests and op­er­a­tion. Re­cov­ery meth­ods for im­per­fect an­neal­ing con­di­tions have been dis­cussed, and a more re­cent pro­posal, the so-called "ni­tric acid soak" has been stud­ied here in de­tail. It shows sur­pris­ing re­cov­ery po­ten­tial, al­beit the un­clear ori­gin of this im­prove­ment. We pre­sent our in­ves­ti­ga­tion on the sev­eral po­ten­tial ori­gins. For this, we used SEM, SIMS and XPS mea­sure­ments of nio­bium sam­ples to study the sur­face mor­phol­ogy and con­t­a­m­i­na­tions. We can re­ject the fa­vored hy­poth­e­sis on the ori­gin of the im­prove­ment, and pro­pose an al­ter­na­tive ori­gin.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK010  
About • Received ※ 10 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 18 June 2022
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TUPOTK011 Commissioning of a New Magnetometric Mapping System for SRF Cavity Performance Tests cavity, SRF, ECR, superconducting-cavity 1215
 
  • J.C. Wolff, J. Eschke, A. Gössel, D. Reschke, L. Steder, L. Trelle
    DESY, Hamburg, Germany
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program.
Mag­netic flux trapped in the nio­bium bulk ma­te­r­ial of su­per­con­duct­ing radio fre­quency (SRF) cav­i­ties de­grades their qual­ity fac­tor and the ac­cel­er­at­ing gra­di­ent. The sen­si­tiv­ity for flux trap­ping is mainly de­ter­mined by the treat­ment and the geom­e­try of the cav­ity as well as the nio­bium grain size and ori­en­ta­tion. To po­ten­tially im­prove the flux ex­pul­sion char­ac­ter­is­tics of SRF cav­i­ties and hence the ef­fi­ciency of fu­ture ac­cel­er­a­tor fa­cil­i­ties, fur­ther stud­ies of the trap­ping be­hav­ior are es­sen­tial. For this pur­pose a mag­ne­to­met­ric map­ping sys­tem to mon­i­tor the mag­netic flux along the outer cav­ity sur­face of 1.3 GHz TESLA-Type sin­gle-cell SRF cav­i­ties has been de­vel­oped and is cur­rently in the com­mis­sion­ing phase at DESY. Con­trary to sim­i­lar ap­proaches, this sys­tem dig­i­tizes the sen­sor sig­nals al­ready in­side of the cryo­stat to ex­ten­sively re­duce the num­ber of re­quired cable feedthroughs. Fur­ther­more, the sig­nal-to-noise ratio (SNR) and con­se­quently the mea­sur­ing sen­si­tiv­ity can be en­hanced by shorter ana­log sig­nal lines, less ther­mal noise and the Mu-metal shield­ing of the cryo­stat. In this con­tri­bu­tion test re­sults gained by a pro­to­type of the map­ping sys­tem are pre­sented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK011  
About • Received ※ 10 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 29 June 2022
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TUPOTK012 Nitrogen Infusion Sample R&D at DESY cavity, vacuum, ECR, accelerating-gradient 1219
 
  • C. Bate
    University of Hamburg, Hamburg, Germany
  • A. Ermakov, D. Reschke, J. Schaffran
    DESY, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program.
Many ac­cel­er­a­tor pro­jects such as the ILC would ben­e­fit from cav­i­ties with re­duced sur­face re­sis­tance (high Q-val­ues) while main­tain­ing a high ac­cel­er­at­ing gra­di­ent. A pos­si­ble way to meet the re­quire­ments is the so-called ni­tro­gen-in­fu­sion pro­ce­dure on Nio­bium cav­i­ties. How­ever, a fun­da­men­tal un­der­stand­ing and a the­o­ret­i­cal model of this method are still miss­ing. One im­por­tant pa­ra­me­ter is the resid­ual re­sis­tance ratio (RRR) which is re­lated to the im­pu­rity con­tent of the ma­te­r­ial. We re­port the in­ves­ti­gated RRR on sam­ples in a wide tem­per­a­ture range in a vac­uum and under a ni­tro­gen at­mos­phere. This com­par­i­son made it pos­si­ble to make state­ments about the dif­fer­ences in the con­cen­tra­tion of ni­tro­gen by vary­ing the tem­per­a­ture. The sam­ples are pure cav­ity-grade nio­bium and treated in the same man­ner as cav­i­ties. For this pur­pose, a small fur­nace ded­i­cated to sam­ple treat­ment was set up to change and ex­plore the pa­ra­me­ter space of the in­fu­sion recipe. Care was taken to achieve the high­est level of pu­rity pos­si­ble in the fur­nace and in a pres­sure range of 1.0·10-8 mbar in order to meet the high re­quire­ments of ni­tro­gen in­fu­sion. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK012  
About • Received ※ 08 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 01 July 2022
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TUPOTK013 PEALD SIS Studies for SRF Cavities cavity, SRF, site, plasma 1222
 
  • I. González Díaz-Palacio, R.H. Blick, A. Stierle, R. Zierold
    University of Hamburg, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • A. Jeromin
    DESY Nanolab, FS-NL, Hamburg, Germany
  • T.F. Keller, N. Krupka, M. Wenskat
    DESY, Hamburg, Germany
  
  Re­cent tech­no­log­i­cal ad­vances and ma­te­r­ial treat­ments have pushed Nb SRF cav­i­ties to their max­i­mum RF per­for­mance. A novel ap­proach for over­com­ing this lim­i­ta­tion, which takes ad­van­tage of RF field only pen­e­trates into the su­per­con­duc­tor at a cer­tain dis­tance called Lon­don pen­e­tra­tion depth, is nano-struc­tur­ing mul­ti­lay­ers with PEALD (plasma-en­hanced atomic layer de­po­si­tion). SIS (su­per­con­duc­tor-in­su­la­tor-su­per­con­duc­tor) mul­ti­lay­ers pro­vide mag­netic screen­ing of the bulk Nb cav­ity, in­creas­ing the field at which the vor­tex pen­e­tra­tion starts, and higher qual­ity fac­tor. ALD is closely re­lated to chem­i­cal vapor de­po­si­tion and bases on se­quen­tial self-limit gas-solid sur­face re­ac­tions fa­cil­i­tat­ing con­for­mal coat­ings with sub-nm pre­ci­sion even on com­plex sub­strates such as the in­te­rior of a cav­ity. As a pre­lim­i­nary study for SIS SRF cav­i­ties, we in­ves­ti­gated the AlN-NbTiN/NbN mul­ti­lay­ers grown by PEALD. Dif­fer­ent com­po­si­tions, thick­nesses, and post-de­po­si­tion ther­mal treat­ments have been in­ves­ti­gated. The char­ac­ter­i­za­tion re­sults of su­per­con­duct­ing prop­er­ties, el­e­men­tal com­po­si­tion, crys­tallinity, and cross-sec­tion are shown in this con­tri­bu­tion.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK013  
About • Received ※ 09 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 27 June 2022
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TUPOTK016 HiPIMS-Coated Novel S(I)S Multilayers for SRF Cavities SRF, cavity, target, cathode 1234
 
  • A.Ö. Sezgin, X. Jiang, M. Vogel
    University Siegen, Siegen, Germany
  • I. González Díaz-Palacio, R. Zierold
    University of Hamburg, Hamburg, Germany
  • S. Keckert, J. Knobloch, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
  
  Funding: Material syntheses and characterizations via SMART, BMBF, Germany (05K19PSA). Superconducting characterizations via iFAST, H2020, EU (101004730). Part of this work via the MNaF, University of Siegen.
Push­ing be­yond the ex­ist­ing bulk nio­bium SRF cav­i­ties is in­dis­pens­able along the path to­wards ob­tain­ing more sus­tain­able next gen­er­a­tion com­pact par­ti­cle ac­cel­er­a­tors. One of the promis­ing can­di­dates to push the lim­its of the bulk nio­bium is thin film-based mul­ti­layer struc­tures in the form of su­per­con­duc­tor-in­su­la­tor-su­per­con­duc­tor (SIS). In this work, S(I)S mul­ti­layer struc­tures were coated by high power im­pulse mag­netron sput­ter­ing (HiP­IMS), hav­ing in­dus­trial up­scal­ing po­ten­tial along with provid-ing higher qual­ity films with re­spect to con­ven­tional mag­netron sput­ter­ing tech­niques (e.g., DCMS), com­bined with (PE)-ALD tech­niques for de­po­si­tion of the ex-situ in­su­lat­ing lay­ers. On the path to­wards for­mu­lat­ing opti-mized recipes for these ma­te­ri­als to be coated on the inner walls of (S)RF cav­i­ties, the re­search fo­cuses on in­no­vat-ing the best per­form­ing S(I)S mul­ti­layer struc­tures con-sist­ing of al­ter­nat­ing su­per­con­duct­ing thin films (e.g., NbN) with in­su­lat­ing lay­ers of metal ni­trides (e.g., AlN) and/or metal ox­ides (e.g., AlxOy) on nio­bium lay-ers/sub­strates (i.e., Nb/AlN/NbN) in com­par­i­son to the so-called SS mul­ti­layer struc­tures (i.e., Nb/NbN). This con-tri­b­u­tion pre­sents the ini­tial ma­te­ri­als and su­per­con­duct-ing and RF char­ac­ter­i­za­tion re­sults of the afore­men­tioned mul­ti­layer sys­tems on flat sam­ples. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK016  
About • Received ※ 11 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 18 June 2022
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TUPOTK018 Combined In-Situ QEXAFS and XRD Investigations on Nb-Treatments in N2 Gas Atmospheres at Elevated Temperatures vacuum, site, cavity, SRF 1238
 
  • P. Rothweiler, F. Eckelt, D. Lützenkirchen-Hecht, S. Paripsa, L. Voß
    University of Wuppertal, Wuppertal, Germany
  
  Funding: We gratefully acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) under project No. 05H18PXRB1.
Thin poly­crys­talline Nb metal foils were treated in N2 gas at­mos­pheres at el­e­vated tem­per­a­tures of 900 °C up to 1200 °C. A com­bi­na­tion of trans­mis­sion mode Quick X-ray ab­sorp­tion spec­troscopy (QEX­AFS) at the Nb-K-edge and X-ray dif­frac­tion (XRD) used in par­al­lel were used to in­ves­ti­gate changes in the atomic short and long-range struc­ture of the bulk Nb-ma­te­r­ial in-situ. A ded­i­cated high-vac­uum heat­ing cell with a base pres­sure of 10-6 mbar was used to per­form the heat treat­ments under vac­uum and ni­tro­gen gas at­mos­phere. The treat­ments typ­i­cally in­cluded (i) a pre­heat­ing at 900 °C under high-vac­uum, (ii) a treat­ment in 3 mbar ni­tro­gen gas at the de­sired tem­per­a­ture and (iii) a cooldown to room tem­per­a­ture under vac­uum con­di­tions. The QEX­AFS and XRD data were col­lected in par­al­lel dur­ing the en­tire process with a time res­o­lu­tion of 4 s. While the sam­ples treated at 900 °C show the typ­i­cal N-up­take to the oc­ta­he­dral in­ter­sti­tial sites, the sam­ples treated at higher tem­per­a­tures show the growth of dis­tinct nio­bium ni­tride phases. The re­sults will be dis­cussed in more de­tails dur­ing the con­fer­ence. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK018  
About • Received ※ 08 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 18 June 2022
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TUPOTK034 Evaluating the Effects of Nitrogen Doping and Oxygen Doping on SRF Cavity Performance cavity, SRF, ECR, simulation 1287
 
  • H. Hu, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia
    Fermilab, Batavia, Illinois, USA
  
  Su­per­con­duct­ing ra­diofre­quency (SRF) cav­i­ties are res­onators with ex­tremely low sur­face re­sis­tance that en­able ac­cel­er­at­ing cav­i­ties to have ex­tremely high qual­ity fac­tors (Q0). High Q0 de­creases the cap­i­tal re­quired to keep the ac­cel­er­a­tors cold by re­duc­ing power loss. The per­for­mance of SRF cav­i­ties is largely gov­erned by the sur­face com­po­si­tion of the first §I{100}{nm} of the cav­ity sur­face. Im­pu­ri­ties such as oxy­gen and ni­tro­gen have been ob­served to yield high Q0, but their pre­cise roles are still being stud­ied. Here, we com­pare the per­for­mance of cav­i­ties doped with ni­tro­gen and oxy­gen in terms of sur­face com­po­si­tion and heat­ing be­hav­ior with field. A sim­u­la­tion of the dif­fu­sion of oxy­gen into the bulk of the cav­ity was built using COM­SOL Mul­ti­physics soft­ware. Sim­u­lated re­sults were com­pared to the ac­tual sur­face com­po­si­tion of the cav­i­ties as de­ter­mined from sec­ondary ion mass spec­trom­e­try analy­sis. Un­der­stand­ing how these im­pu­ri­ties af­fects per­for­mance al­lows us to have fur­ther in­sight into the un­der­ly­ing mech­a­nisms that en­able these sur­face treat­ments to yield high Q0.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK034  
About • Received ※ 08 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 30 June 2022
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TUPOTK035 CVD Nb3Sn-on-Copper SRF Accelerator Cavities cavity, SRF, radio-frequency, factory 1291
 
  • G. Gaitan, P.N. Koufalis, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • V.M. Arrieta, S.R. McNeal
    Ultramet, Pacoima, California, USA
  • M. Liepe
    Cornell University, Ithaca, New York, USA
  
  Funding: This work is supported by the US Department of Energy SBIR program under grant number DE-SC0017902. Gabriel Gaitan is supported by the National Science Foundation under Grant No. PHY-1549132.
Nb3Sn is the most promis­ing al­ter­na­tive ma­te­r­ial for achiev­ing su­pe­rior per­for­mance in Su­per­con­duct­ing Ra­dio-Fre­quency (SRF) cav­i­ties, com­pared to con­ven­tional bulk Nb cav­i­ties now used in ac­cel­er­a­tors. Chem­i­cal vapor de­po­si­tion (CVD) is an al­ter­na­tive to the vapor dif­fu­sion-based Nb3Sn growth tech­nique pre­dom­i­nantly used on bulk nio­bium cav­i­ties and may en­able reach­ing su­pe­rior RF per­for­mance at re­duced cost. In col­lab­o­ra­tion with Cor­nell, Ul­tra­met has de­vel­oped CVD process ca­pa­bil­i­ties and re­ac­tor de­signs to coat cop­per SRF cav­i­ties with thick and thin films of Nb and Nb3Sn. In this paper, we pre­sent our lat­est re­search ef­forts on CVD Nb3Sn-on-cop­per SRF cav­i­ties, in­clud­ing RF per­for­mance test re­sults from two 1.3 GHz SRF cav­i­ties coated by Ul­tra­met. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK035  
About • Received ※ 15 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 21 June 2022
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TUPOTK036 Study of Chemical Treatments to Optimize Niobium-3 Tin Growth in the Nucleation Phase cavity, SRF, radio-frequency, site 1295
 
  • L. Shpani, S.G. Arnold, G. Gaitan, M. Liepe, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T. Arias, M.M. Kelley, N. Sitaraman
    Cornell University, Ithaca, New York, USA
  
  Funding: This research is funded by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beams.
Nio­bium-3 Tin (Nb3Sn) is a high-po­ten­tial ma­te­r­ial for next-gen­er­a­tion Su­per­con­duct­ing Ra­diofre­quency (SRF) cav­i­ties in par­ti­cle ac­cel­er­a­tors. The most promis­ing growth method to date is based on vapor dif­fu­sion of tin into a nio­bium sub­strate with nu­cle­at­ing agent Tin Chlo­ride (SnCl2). Still, the cur­rent vapor dif­fu­sion recipe has sig­nif­i­cant room for re­al­iz­ing fur­ther per­for­mance im­prove­ment. We are in­ves­ti­gat­ing how dif­fer­ent chem­i­cal treat­ments on the nio­bium sub­strate be­fore coat­ing in­flu­ence the growth of a smooth and uni­form Nb3Sn layer. More specif­i­cally, this study fo­cuses on the in­ter­ac­tion be­tween the SnCl2 nu­cle­at­ing agent and the nio­bium sur­face ox­ides. We com­pare the ef­fect of dif­fer­ent chem­i­cal treat­ments with dif­fer­ent pH val­ues on the tin droplet dis­tri­b­u­tion on nio­bium after the nu­cle­ation stage of coat­ing. We also look at the ef­fect that the nu­cle­ation tem­per­a­ture has on the smooth­ness and uni­for­mity of the tin dis­tri­b­u­tion, with the ul­ti­mate goal of op­ti­miz­ing the recipe to coat smooth Nb3Sn cav­i­ties. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK036  
About • Received ※ 12 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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TUPOTK042 Challenges to Reliable Production Nitrogen Doping of Nb for SRF Accelerating Cavities cavity, SRF, vacuum, controls 1311
 
  • C.E. Reece, M.J. Kelley, E.M. Lechner, A.D. Palczewski
    JLab, Newport News, Virginia, USA
  • J.W. Angle, M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • F.A. Stevie
    NCSU AIF, Raleigh, North Carolina, USA
  
  Funding: This work was authored by JSA LLC under U.S. DOE contract DE-AC05-06OR23177. This material is based on work supported by the U.S. DOE Early Career Award to A. Palczewski, with supplemental support from DOE BES via the LCLS-II HE R&D program. J. Angle’s support was from the Office of High Energy Physics, under grant DE-SC-0014475 to Virginia Tech.
Over the last sev­eral years, al­loy­ing of the sur­face layer of nio­bium SRF cav­i­ties has been demon­strated to ben­e­fi­cially lower the su­per­con­duct­ing RF sur­face re­sis­tance. Ni­tro­gen, ti­ta­nium, and oxy­gen have all been demon­strated as ef­fec­tive al­loy­ing agents, oc­cu­py­ing in­ter­sti­tial sites in the nio­bium lat­tice within the RF pen­e­tra­tion depth and even deeper, when al­lowed to ther­mally dif­fuse into the sur­face at ap­pro­pri­ate tem­per­a­tures. The use of ni­tro­gen for this func­tion has been often termed ’ni­tro­gen dop­ing’ and is being ap­plied in the LCLS-II and LCLS-II HE pro­jects. We re­port char­ac­ter­i­za­tion stud­ies of the dis­tri­b­u­tion of ni­tro­gen into the ex­posed nio­bium sur­face and how such dis­tri­b­u­tion is af­fected by the qual­ity of the vac­uum fur­nace en­vi­ron­ment in which the dop­ing takes place, and the com­plex­ity of ni­tride crys­tal growth on dif­fer­ent grain ori­en­ta­tions of sur­face nio­bium. Using state-of-the-art quan­tifi­ca­tion meth­ods by dy­namic sec­ondary ion mass spec­trom­e­try (SIMS) depth pro­fil­ing in nio­bium, we iden­tify sev­eral phe­nom­ena in­volv­ing fur­nace-sourced con­t­a­m­i­na­tion. We also high­light a po­ten­tial issue with N2 flow con­straints from the flange ’caps’ used dur­ing heat treat­ments. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK042  
About • Received ※ 07 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 05 July 2022
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TUPOTK044 Preliminary Results of a Magnetic and Temperature Map System for 3 GHz Superconducting Radio Frequency Cavities cavity, SRF, MMI, radio-frequency 1315
 
  • I.P. Parajuli, G. Ciovati, J.R. Delayen, A.V. Gurevich, B.D. Khanal
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, J.R. Delayen
    JLab, Newport News, Virginia, USA
  
  Funding: Work supported by NSF Grant 100614-010. Jlab work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Su­per­con­duct­ing radio fre­quency (SRF) cav­i­ties are fun­da­men­tal build­ing blocks of mod­ern par­ti­cle ac­cel­er­a­tors. A sur­face re­sis­tance in the tens of nanoOhm range is achieved when cool­ing these cav­i­ties to liq­uid he­lium tem­per­a­ture, ~2 - 4 K. One of the lead­ing sources of resid­ual losses in SRF cav­i­ties is trapped mag­netic flux. Flux trap­ping mech­a­nism de­pends on dif­fer­ent sur­face prepa­ra­tions and cool-down con­di­tions. We have de­signed, de­vel­oped and com­mis­sioned a com­bined mag­netic and tem­per­a­ture map­ping sys­tem using anisotropic mag­neto-re­sis­tance sen­sors and car­bon re­sis­tors, re­spec­tively, to study the flux trap mech­a­nism in 3 GHz sin­gle-cell nio­bium cav­i­ties. In this con­tri­bu­tion, we will de­scribe the ex­per­i­men­tal ap­pa­ra­tus and pre­sent pre­lim­i­nary test re­sults. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK044  
About • Received ※ 02 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 24 June 2022 — Issue date ※ 25 June 2022
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TUPOTK045 Magnetic Field Mapping of 1.3 GHz Superconducting Radio Frequency Niobium Cavities cavity, SRF, MMI, radio-frequency 1319
 
  • I.P. Parajuli, G. Ciovati, J.R. Delayen, A.V. Gurevich
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, J.R. Delayen
    JLab, Newport News, Virginia, USA
  
  Funding: Work supported by NSF Grant 100614-010. Jlab work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Nio­bium is the ma­te­r­ial of choice to build su­per­con­duct­ing radio fre­quency (SRF) cav­i­ties, which are fun­da­men­tal build­ing blocks of mod­ern par­ti­cle ac­cel­er­a­tors. These cav­i­ties re­quire a cryo­genic cool-down to ~2 - 4 K for op­ti­mum per­for­mance min­i­miz­ing RF losses on the inner cav­ity sur­face. How­ever, tem­per­a­ture-in­de­pen­dent resid­ual losses in SRF cav­i­ties can­not be pre­vented en­tirely. One of the sig­nif­i­cant con­trib­u­tor to resid­ual losses is trapped mag­netic flux. The flux trap­ping mech­a­nism de­pends on dif­fer­ent fac­tors, such as sur­face prepa­ra­tions and cool-down con­di­tions. We have de­vel­oped a di­ag­nos­tic mag­netic field scan­ning sys­tem (MFSS) using Hall probes and anisotropic mag­neto-re­sis­tance sen­sors to study the spa­tial dis­tri­b­u­tion of trapped flux in 1.3 GHz sin­gle-cell cav­i­ties. The first re­sult from this newly com­mis­sioned sys­tem re­vealed that the trapped flux on the cav­ity sur­face might re­dis­trib­ute with in­creas­ing RF power. The MFSS was also able to cap­ture sig­nif­i­cant mag­netic field en­hance­ment at spe­cific cav­ity lo­ca­tions after a quench. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK045  
About • Received ※ 02 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 20 June 2022 — Issue date ※ 27 June 2022
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TUPOTK059 Modeling O and N Alloying in Nb for SRF Applications cavity, SRF, radio-frequency, vacuum 1354
 
  • E.M. Lechner, M.J. Kelley, A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • J.W. Angle, M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • F.A. Stevie
    NCSU AIF, Raleigh, North Carolina, USA
  
  Funding: This work was coauthored by Jefferson Science Associates LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and grant No. DE-SC-0014475 to Virginia Tech for the support of J. Angle.
N and O-al­loyed su­per­con­duct­ing radio fre­quency cav­i­ties ex­hibit ex­tra­or­di­nary qual­ity fac­tors. De­vel­op­ing dif­fu­sion mod­els that de­scribe in­ter­sti­tial N and O in Nb is im­por­tant for op­ti­miz­ing al­loyed cav­ity qual­ity fac­tors and ac­cel­er­at­ing gra­di­ents. N and O-al­loyed Nb sam­ples are ex­am­ined with SEM AND SIMS and their dif­fu­sion pro­files mod­eled. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK059  
About • Received ※ 08 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 17 June 2022
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THPOMS052 Magnetic Field Shield for SC-Cavity with Thin Nb Sheet cavity, shielding, experiment, cryogenics 3090
 
  • Y. Iwashita, Y. Kuriyama
    Kyoto University, Research Reactor Institute, Osaka, Japan
  • Y. Fuwa
    JAEA/J-PARC, Tokai-mura, Japan
  • H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  
  Funding: This work was partly supported by JSPS KAKENHI Grant Number 19K21877.
Shield­ing the su­per­con­duct­ing ac­cel­er­at­ing cav­ity made of nio­bium from the weak en­vi­ron­men­tal mag­netic field is an im­por­tant sub­ject. Nio­bium is a type-II su­per­con­duc­tor, which traps the en­vi­ron­men­tal mag­netic flux in the ma­te­r­ial dur­ing the su­per­con­duct­ing tran­si­tion, re­sult­ing in in­crease of resid­ual re­sis­tance and heat­ing dur­ing op­er­a­tion dur­ing op­er­a­tion. Shield­ing from a weak mag­netic field is es­sen­tial for high per­for­mance op­er­a­tions. A mag­netic shield­ing method that uses the dia­mag­net­ism of su­per­con­duct­ing ma­te­ri­als in­stead of mag­netic flux ab­sorp­tion by high mag­netic per­me­abil­ity ma­te­ri­als is dis­cussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOMS052  
About • Received ※ 14 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 18 June 2022
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