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

Abstract

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 Q0 (3.0×1010) also exceeded its specification (2.7×1010). 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.15 MoreReceived 27 October 2021Accepted 15 February 2022DOI:https://doi.org/10.1103/PhysRevAccelBeams.25.042001Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCryogenics & vacuum technologySuperconducting RFSuperconductivityPhysical SystemsLinear acceleratorsAccelerators & Beams