• Open Access

Mitigation of multipacting in 113 MHz superconducting rf photoinjector

I. Petrushina, V. N. Litvinenko, I. Pinayev, K. Smith, G. Narayan, and F. Severino
Phys. Rev. Accel. Beams 21, 082001 – Published 13 August 2018

Abstract

Superconducting rf (SRF) photoinjectors are one of the most promising devices for generating continuous wave (CW) electron beams with record high brightness. Ultrahigh vacuum of SRF guns provides for long lifetime of the high quantum efficiency (QE) photocathodes, while SRF technology provides for high accelerating gradients exceeding 10MV/m. It is especially true for low frequency SRF guns where electrons are generated at photocathodes at the crest of accelerating voltage. Two main physics challenges of SRF guns are their compatibility with high QE photocathodes and multipacting. The first is related to a possibility of deposition of photocathode materials (such as Cs) on the walls of the SRF cavity, which can result in increased dark current via reduction of the bulk Nb work function and in enhancing of a secondary electron emission yield (SEY). SEY plays critical role in multipacting (e.g., an exponential growth of the multipactor discharge), which could both spoil the gun vacuum and speed up the deposition of the cathode material on the walls of the SRF cavity. In short, the multipactor behavior in superconducting accelerating units must be well understood for successful operation of an SRF photo-injector. In this paper we present our studies of 1.2 MV 113 MHz quarter-wave SRF photoinjector serving as a source of electron beam for the coherent electron cooling experiment (CeC) at BNL. During three years of operating our SRF gun we encountered a number of multipacting zones. We also observed that presence of CsK2Sb photocathode in the gun could create additional multipacting barriers. We had conducted a comprehensive numerical and experimental study of the multipactor discharge in our SRF gun. We had developed a process of crossing the multipacting barriers from zero to the operational voltage without affecting the lifetime of our photocathode and enhancing the strength of multipacting barriers. We found a good agreement between the results of simulations and our experimental data.

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  • Received 28 February 2018

DOI:https://doi.org/10.1103/PhysRevAccelBeams.21.082001

Published 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 Society

Physics Subject Headings (PhySH)

Accelerators & Beams

Authors & Affiliations

I. Petrushina1,2,*, V. N. Litvinenko1,2, I. Pinayev2, K. Smith2, G. Narayan2, and F. Severino2

  • 1Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
  • 2Collider-Accelerator Department, Brookhaven National Laboratory, Upton, New York 11973, USA

  • *ipetrushina@bnl.gov

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Vol. 21, Iss. 8 — August 2018

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