Author: Popielarski, J.T.
Paper Title Page
MOPA83 Automation of Superconducting Cavity and Superconducting Magnet Operation for FRIB 239
 
  • W. Chang, Y. Choi, X.-J. Du, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, H. Nguyen, J.T. Popielarski, K. Saito, T. Xu, S. Zhao
    FRIB, East Lansing, Michigan, USA
 
  The su­per­con­duct­ing (SC) dri­ver linac for the Fa­cil­ity for Rare Iso­tope Beams (FRIB) is a heavy-ion ac­cel­er­a­tor that ac­cel­er­ate ions to 200 MeV per nu­cleon. The linac has 46 cry­omod­ules that con­tain 324 SC cav­i­ties and 69 SC so­le­noid pack­ages. For linac op­er­a­tion with high avail­abil­ity and high re­li­a­bil­ity, au­toma­tion is es­sen­tial for such tasks as fast de­vice turn-on/off, fast re­cov­ery from trips, and real-time mon­i­tor­ing of op­er­a­tional per­for­mance. We have im­ple­mented sev­eral au­toma­tion al­go­rithms, in­clud­ing one-but­ton turn-on/off of SC cav­i­ties and SC mag­nets; au­to­mated de­gauss­ing of SC so­le­noids; mit­i­ga­tion of field emis­sion-in­duced mul­ti­pact­ing dur­ing re­cov­ery from cav­ity trips; and real-time mon­i­tor­ing of the cav­ity field level cal­i­bra­tion. The de­sign, de­vel­op­ment, and op­er­at­ing ex­pe­ri­ence with au­toma­tion will be pre­sented.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA83  
About • Received ※ 02 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 26 August 2022
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MOPA84 Superconducting Cavity Commissioning for the FRIB Linac 242
 
  • W. Chang, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, J.T. Popielarski, K. Saito, T. Xu, S. Zhao
    FRIB, East Lansing, Michigan, USA
 
  The su­per­con­duct­ing dri­ver linac for the Fa­cil­ity for Rare Iso­tope Beams (FRIB) is a heavy ion ac­cel­er­a­tor that has 46 cry­omod­ules with 324 su­per­con­duct­ing (SC) cav­i­ties that ac­cel­er­ate ions to 200 MeV per nu­cleon. Linac com­mis­sion­ing was done in mul­ti­ple phases, in par­al­lel with tech­ni­cal in­stal­la­tion. Ion beam have now been ac­cel­er­ated to the de­sign en­ergy through the full linac; rare iso­topes were first pro­duced in De­cem­ber 2021; and the first user ex­per­i­ment was com­pleted in May 2022. All cry­omod­ules were suc­cess­fully com­mis­sioned. Cry­omod­ule com­mis­sion­ing in­cluded es­tab­lish­ing the de­sired cav­ity fields, mea­sur­ing field emis­sion X-rays, op­ti­miz­ing the tuner con­trol loops, mea­sur­ing the cav­ity dy­namic heat load, and con­firm­ing the low-level RF con­trol (am­pli­tude and phase sta­bil­ity). Re­sults on cry­omod­ule com­mis­sion­ing and cry­omod­ule per­for­mance will be pre­sented.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA84  
About • Received ※ 13 July 2022 — Revised ※ 02 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 05 September 2022
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MOPA85 Design of a 185.7 MHz Superconducting RF Photoinjector Quarter-Wave Resonator for the LCLS-II-HE Low Emittance Injector 245
 
  • S.H. Kim, W. Hartung, T. Konomi, S.J. Miller, M.S. Patil, J.T. Popielarski, K. Saito, T. Xu, T. Xu
    FRIB, East Lansing, Michigan, USA
  • C. Adolphsen, L. Ge, F. Ji, J.W. Lewellen, L. Xiao
    SLAC, Menlo Park, California, USA
  • M.P. Kelly, T.B. Petersen, P. Piot
    ANL, Lemont, Illinois, USA
  • P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
 
  Funding: Work supported by the U.S. Department of Energy Contract DE-AC02-76SF00515.
A 185.7 MHz su­per­con­duct­ing quar­ter-wave res­onator (QWR) was de­signed for the low emit­tance in­jec­tor of the Linac Co­her­ent Light Source high en­ergy up­grade (LCLS-II-HE). The cav­ity was de­signed to min­i­mize the risk of cath­ode ef­fi­ciency degra­da­tion due to mul­ti­pact­ing or field emis­sion and to op­er­ate with a high RF elec­tric field at the cath­ode for low elec­tron-beam emit­tance. Cav­ity de­sign fea­tures in­clude: (1) shap­ing of the cav­ity wall to re­duce the strength of the low-field coax­ial mul­ti­pact­ing bar­rier; (2) four ports for elec­trop­o­l­ish­ing and high-pres­sure water rins­ing; and (3) a fun­da­men­tal power cou­pler (FPC) port lo­cated away from the ac­cel­er­at­ing gap. The de­sign is ori­ented to­ward min­i­miz­ing the risk of par­tic­u­late con­t­a­m­i­na­tion and avoid harm­ful di­pole com­po­nents in the RF field. The ANL 162 MHz FPC de­sign for PIP-II is being adapted for the gun cav­ity. We will pre­sent the RF de­sign of the cav­ity in­te­grated with the FPC.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA85  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022
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MOPA86 Conditioning of Low-Field Multipacting Barriers in Superconducting Quarter-Wave Resonators 249
 
  • S.H. Kim, W. Chang, W. Hartung, J.T. Popielarski, T. Xu
    FRIB, East Lansing, Michigan, USA
 
  Funding: This is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University.
Mul­ti­pact­ing (MP) bar­ri­ers are typ­i­cally ob­served at very low RF am­pli­tude, at a field 2 to 3 or­ders of mag­ni­tude below the op­er­at­ing gra­di­ent, in low-fre­quency (<~100 MHz), quar­ter-wave res­onators (QWRs). Such bar­ri­ers may be trou­ble­some, as RF con­di­tion­ing with a fun­da­men­tal power cou­pler (FPC) of typ­i­cal cou­pling strength (ex­ter­nal Q = 106 to 107) is gen­er­ally dif­fi­cult. For the FRIB \beta = 0.085 QWRs (80.5 MHz), the low bar­rier is ob­served at an ac­cel­er­at­ing gra­di­ent (Eacc) of ~10 kV/m; the op­er­at­ing Eacc is 5.6 MV/m. The­o­ret­i­cal and sim­u­la­tion stud­ies sug­gested that the con­di­tion­ing is dif­fi­cult due to the rel­a­tively low RF power dis­si­pated into mul­ti­pact­ing rather than being a prob­lem of the low bar­rier being stronger than other bar­ri­ers. We de­vel­oped a sin­gle-stub coax­ial FPC match­ing el­e­ment for ex­ter­nal ad­just­ment of the ex­ter­nal Q by one order of mag­ni­tude. The match­ing el­e­ment pro­vided a sig­nif­i­cant re­duc­tion in the time to con­di­tion the low bar­rier. We will pre­sent the­o­ret­i­cal and sim­u­la­tion stud­ies of the low MP bar­rier and ex­per­i­men­tal re­sults on MP con­di­tion­ing with the sin­gle-stub FPC match­ing el­e­ment.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA86  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022
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MOPA87 Design of the Cathode Stalk for the LCLS-II-HE Low Emittance Injector 253
 
  • T. Konomi, W. Hartung, S.H. Kim, S.J. Miller, D.G. Morris, J.T. Popielarski, K. Saito, A. Taylor, T. Xu
    FRIB, East Lansing, Michigan, USA
  • C. Adolphsen, J.W. Lewellen
    SLAC, Menlo Park, California, USA
  • S. Gatzmaga, P. Murcek, R. Xiang
    HZDR, Dresden, Germany
  • M.P. Kelly, T.B. Petersen
    ANL, Lemont, Illinois, USA
 
  Su­per­con­duct­ing ra­dio-fre­quency (SRF) elec­tron guns are at­trac­tive for de­liv­ery of beams at a high bunch rep­e­ti­tion rate with a high ac­cel­er­at­ing field. An SRF gun is the most suit­able in­jec­tor for the high-en­ergy up­grade of the Linac Co­her­ent Light Source (LCLS-II-HE), which will pro­duce high-en­ergy X-rays at high rep­e­ti­tion rate. An SRF gun is being de­vel­oped for LCLS-II-HE as a col­lab­o­ra­tive ef­fort by FRIB, HZDR, ANL, and SLAC. The cav­ity op­er­at­ing fre­quency is 185.7 MHz, and the tar­get ac­cel­er­at­ing field at the pho­to­cath­ode is 30 MV/m. The pho­to­cath­ode is re­place­able. The cath­ode is held by a fix­ture (’cath­ode stalk’) that is de­signed for ther­mal iso­la­tion and par­ti­cle-free cath­ode ex­change. The stalk must allow for pre­cise align­ment of the cath­ode po­si­tion, cryo­genic or room-tem­per­a­ture cath­ode op­er­at­ing tem­per­a­ture, and DC bias to in­hibit mul­ti­pact­ing. We are plan­ning a test of the stalk to con­firm that the de­sign meets the re­quire­ments for RF power dis­si­pa­tion and bi­as­ing. In this pre­sen­ta­tion, we will de­scribe the cath­ode stalk de­sign and RF/DC stalk test plan.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA87  
About • Received ※ 04 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 18 August 2022 — Issue date ※ 11 September 2022
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MOPA91 Plasma Processing of Superconducting Quarter-Wave Resonators Using a Higher-Order Mode 267
 
  • W. Hartung, W. Chang, K. Elliott, S.H. Kim, T. Konomi, J.T. Popielarski, K. Saito, T. Xu
    FRIB, East Lansing, Michigan, USA
 
  The Fa­cil­ity for Rare Iso­tope Beams (FRIB) is a su­per­con­duct­ing ion linac with ac­cel­er­a­tion pro­vided by 104 quar­ter-wave res­onators (QWRs) and 220 half-wave res­onators (HWRs); FRIB user op­er­a­tions began in May 2022. Plasma clean­ing is being de­vel­oped as a method to mit­i­gate pos­si­ble fu­ture degra­da­tion of QWR or HWR per­for­mance: in-situ plasma clean­ing rep­re­sents an al­ter­na­tive to re­moval and dis­as­sem­bly of cry­omod­ules for re­fur­bish­ment of each cav­ity via re­peat etch­ing and rins­ing. Ini­tial mea­sure­ments were done on a QWR and an HWR with room-tem­per­a­ture-matched input cou­plers to drive the plasma via the fun­da­men­tal mode. Sub­se­quent plasma clean­ing tests were done on two ad­di­tional FRIB QWRs using the fun­da­men­tal power cou­pler (FPC) to drive the plasma. When using the FPC, a higher-or­der mode (HOM) at 5 times the ac­cel­er­at­ing mode fre­quency was used to drive the plasma. Use of the HOM al­lowed for less mis­match at the FPC and hence lower field in the cou­pler rel­a­tive to the cav­ity. A neon-oxy­gen gas mix­ture was used for plasma gen­er­a­tion. Be­fore and after cold tests showed a sig­nif­i­cant re­duc­tion in field emis­sion X-rays after plasma clean­ing. Re­sults will be pre­sented.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA91  
About • Received ※ 12 August 2022 — Revised ※ 16 August 2022 — Accepted ※ 25 August 2022 — Issue date ※ 16 September 2022
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WEPA03 Status of the SLAC/MSU SRF Gun Development Project 623
 
  • J.W. Lewellen, C. Adolphsen, R. Coy, L. Ge, F. Ji, M.J. Murphy, L. Xiao
    SLAC, Menlo Park, California, USA
  • A. Arnold, S. Gatzmaga, P. Murcek, R. Xiang
    HZDR, Dresden, Germany
  • Y. Choi, C. Compton, X.-J. Du, D.B. Greene, W. Hartung, S.H. Kim, T. Konomi, S.J. Miller, D.G. Morris, M.S. Patil, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu
    FRIB, East Lansing, Michigan, USA
  • M.P. Kelly, T.B. Petersen
    ANL, Lemont, Illinois, USA
 
  Funding: US Department of Energy.
The LCLS-II-HE pro­ject at SLAC is in­tended to in­crease the pho­ton en­ergy reach of the LCLS-II FEL to at least 20 keV. In ad­di­tion to up­grad­ing the un­du­la­tor sys­tem, and in­creas­ing the elec­tron beam en­ergy to 8 GeV, the pro­ject will also con­struct a low-emit­tance in­jec­tor (LEI) in a new tun­nel. To achieve the LEI emit­tance goals, a low-MTE pho­to­cath­ode will be re­quired, as will on-cath­ode elec­tric fields up to 50% higher than those achiev­able in the cur­rent LCLS-II pho­toin­jec­tor. The beam source for the LEI will be based around a su­per­con­duct­ing quar­ter­wave cav­ity res­o­nant at 185.7 MHz. A pro­to­type gun is cur­rently being de­signed and fab­ri­cated at the Fa­cil­ity for Rare Iso­tope Beams (FRIB) at Michi­gan State Uni­ver­sity. This paper pre­sents the per­for­mance goals for the new gun de­sign, an overview of the pro­to­type de­vel­op­ment ef­fort, cur­rent sta­tus, and fu­ture plans in­clud­ing fab­ri­ca­tion of a "pro­duc­tion" gun for the LEI.
 
poster icon Poster WEPA03 [4.510 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA03  
About • Received ※ 21 July 2022 — Revised ※ 28 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 11 August 2022
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