Update on Plasma Processing R&D for LCLS-II
Paolo Berrutti, M. Doléans, Daniel Gonnella, Anna Grassellino, Timergali N. Khabiboulline, Sang-Ho Kim, G. Lanza, Martina Martinello, Marc C Ross, Kristin Tippey · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2018
SRF cavities performance preservation is crucial, from vertical test to accelerator operation. Field emission is still one of the main problems to overcome and plasma cleaning has been proven successful by SNS, in cleaning field emitters and increasing the work function of Nb. A collaboration has been established between FNAL, SLAC and ORNL with the purpose of applying plasma processing to LCLS-II cavities, in order to minimize and overcome field emission without affecting the high Q of N-doped cavities. The recipe will follow the neon-oxygen active plasma adopted at SNS, allowing in-situ processing of cavities and cryomodules from hydrocarbon contaminants. A novel method for plasma ignition has been developed at FNAL: a plasma glow discharge is ignited using high order modes to overcome limitations imposed by the fundamental power coupler. The results of experiments on 9-cell LCLS-II cavity are presented, along with plasma ignition studies. In addition the RF system is shown and N-doped Nb samples studies are discussed.