Author: Sikora, J.P.
Paper Title Page
MOPA12 Commissioning of HOM Detectors in the First Cryomodule of the LCLS-II Linac 69
 
  • J.A. Diaz Cruz
    UNM-ECE, Albuquerque, USA
  • B.T. Jacobson, N.R. Neveu, J.P. Sikora
    SLAC, Menlo Park, California, USA
 
  Long-range wake­fields (LRWs) may cause emit­tance di­lu­tion ef­fects. LWRs are es­pe­cially un­wanted at fa­cil­i­ties with low emit­tance beams like the LCLS-II at SLAC. Dipo­lar higher-or­der modes (HOMs) are a set of LRWs that are ex­cited by off-axis beams. Two 4-chan­nel HOM de­tec­tors were built to mea­sure the beam-in­duced HOM sig­nals for TESLA-type su­per­con­duct­ing RF (SRF) cav­i­ties; they were tested at the Fer­mi­lab Ac­cel­er­a­tor Sci­ence and Tech­nol­ogy (FAST) fa­cil­ity and are now in­stalled at SLAC. The HOM de­tec­tors were de­signed to in­ves­ti­gate LRW ef­fects on the beam and to help with beam align­ment. This paper pre­sents pre­lim­i­nary re­sults of HOM mea­sure­ments at the first cry­omod­ule (CM01) of the LCLS-II linac and de­scribes the rel­e­vant hard­ware and setup of the ex­per­i­ment.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA12  
About • Received ※ 09 August 2022 — Accepted ※ 20 August 2022 — Issue date ※ 31 August 2022  
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MOPA30 LCLS-II BCS Average Current Monitor 120
 
  • N.M. Ludlow, T.L. Allison, J.P. Sikora, J.J. Welch
    SLAC, Menlo Park, California, USA
 
  LCLS-II is a 4th gen­er­a­tion light source at the SLAC Na­tional Ac­cel­er­a­tor Lab­o­ra­tory. LCLS-II will ac­cel­er­ate a 30 µA elec­tron beam with a 1 MHz bunch rate with a new su­per­con­duct­ing Con­tin­u­ous Wave­form (CW) RF ac­cel­er­a­tor. The Av­er­age Cur­rent Mon­i­tor (ACM) is part of the Beam Con­tain­ment Sys­tem (BCS) for the LCLS-II ac­cel­er­a­tor. The Beam Con­tain­ment Sys­tem is a safety sys­tem that pro­vides paths to safely shut the ac­cel­er­a­tor beam off under a va­ri­ety of con­di­tions. The Av­er­age Cur­rent Mon­i­tor is a beam di­ag­nos­tic within the BCS that is used to ver­ify that the ac­cel­er­a­tor is pro­duc­ing the ap­pro­pri­ate cur­rent level and to limit beam power to al­lowed val­ues to pro­tect the ma­chine and beam dumps. The av­er­age beam cur­rent is ob­tained by mea­sur­ing the power level in­duced by the beam in a low Q cav­ity. By know­ing the Q, the beta, and the cou­pling of the cav­ity, the in­stan­ta­neous charge can be cal­cu­lated, then in­te­grat­ing the in­stan­ta­neous charge over one mil­lisec­ond will yield the av­er­age cur­rent. This paper will dis­cuss progress in the check­out process of the ACM LLRF hard­ware lead­ing to LCLS-II com­mis­sion­ing.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA30  
About • Received ※ 16 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 24 August 2022 — Issue date ※ 06 October 2022
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