In-situ plasma processing to increase the accelerating gradients of superconducting radio-frequency cavities

M. Doleans, P. V. Tyagi, R. Afanador, C. J. McMahan, J. A. Ball, D. L. Barnhart, W. Blokland, M. T. Crofford, B. D. Degraff, S. W. Gold, B. S. Hannah, M. P. Howell, S. H. Kim, S. W. Lee, J. Mammosser, T. S. Neustadt, J. W. Saunders, S. Stewart, W. H. Strong, D. J. VandygriffD. M. Vandygriff

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

A new in-situ plasma processing technique is being developed at the Spallation Neutron Source (SNS) to improve the performance of the cavities in operation. The technique utilizes a low-density reactive oxygen plasma at room temperature to remove top surface hydrocarbons. The plasma processing technique increases the work function of the cavity surface and reduces the overall amount of vacuum and electron activity during cavity operation; in particular it increases the field emission onset, which enables cavity operation at higher accelerating gradients. Experimental evidence also suggests that the SEY of the Nb surface decreases after plasma processing which helps mitigating multipacting issues. In this article, the main developments and results from the plasma processing R&D are presented and experimental results for in-situ plasma processing of dressed cavities in the SNS horizontal test apparatus are discussed.

Funding

We would like to thank Percy Harrell and Dale Heidenreich for their help during the tests with the HTA. This manuscript has been authored by UT-Battelle, LLC under Contract no. DE-AC05-00OR22725 with the U.S. Department of Energy .

Keywords

  • Linear accelerator
  • Plasma processing
  • SRF technology

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