Author: McMullin, M.W.
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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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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
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)