Physical Review Accelerators and Beams (Apr 2022)

High gradient performance and quench behavior of a verification cryomodule for a high energy continuous wave linear accelerator

  • S. Posen,
  • A. Cravatta,
  • M. Checchin,
  • S. Aderhold,
  • C. Adolphsen,
  • T. Arkan,
  • D. Bafia,
  • A. Benwell,
  • D. Bice,
  • B. Chase,
  • C. Contreras-Martinez,
  • L. Doolittle,
  • J. Fuerst,
  • D. Gonnella,
  • A. Grassellino,
  • C. Grimm,
  • B. Hansen,
  • E. Harms,
  • B. Hartsell,
  • G. Hays,
  • J. Holzbauer,
  • S. Hoobler,
  • J. Kaluzny,
  • T. Khabiboulline,
  • M. Kucera,
  • D. Lambert,
  • R. Legg,
  • F. Lewis,
  • J. Makara,
  • H. Maniar,
  • J. T. Maniscalco,
  • M. Martinello,
  • J. Nelson,
  • S. Paiagua,
  • Y. Pischalnikov,
  • P. Prieto,
  • J. Reid,
  • M. Ross,
  • C. Serrano,
  • N. Solyak,
  • A. Syed,
  • D. Sun,
  • G. Tatkowski,
  • R. Wang,
  • M. White,
  • L. Zacarias

DOI
https://doi.org/10.1103/PhysRevAccelBeams.25.042001
Journal volume & issue
Vol. 25, no. 4
p. 042001

Abstract

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An eight-cavity, 1.3 GHz, SLAC linac coherent light source II High Energy cryomodule was assembled and tested at Fermilab to verify performance before the start of production. Its cavities were processed with a novel nitrogen doping treatment to improve gradient performance. The cryomodule was tested with a modified protocol to process sporadic quenches, which were observed in Linac Coherent Light Source II production cryomodules and are attributed to multipacting. Dedicated vertical test experiments support the attribution to multipacting. The verification cryomodule achieved an acceleration voltage of 200 MV in continuous wave mode, corresponding to an average accelerating gradient of 24.1 MV/m, significantly exceeding the specification of 173 MV. The average Q_{0} (3.0×10^{10}) also exceeded its specification (2.7×10^{10}). After processing, no field emission was observed up to the maximum gradient of each cavity. This paper reviews the cryomodule performance and discusses operational issues and mitigations implemented during the several month program.