Field emission mitigation studies in the SLAC Linac Coherent Light Source II superconducting rf cavities via <i>in situ</i> plasma processing

Field emission is one of the main factors that can limit performance superconducting radio frequency cavities. To reduce possible field in Linac Coherent Light Source II (LCLS-II), we are developing plasma processing for 1.3 GHz nine-cell The ultimate goal will be to apply technique situ cryomodules order mitigate hydrocarbon-related without disassembling them. Herein presented first systematic study applied LCLS-II Having developed a new method ignition cavities, cavities starting with clean nitrogen doped cavity and proceeding studying natural artificially contaminated All were cold tested before after cleaning compare their performances. It was proved this successfully removes carbon-based contamination from iris it able eliminate naturally emitting cavity. effect on exposed vacuum failures also investigated, showing positive results some cases. This work shows how successful removing hydrocarbon related surface affecting high Q-factors quench fields characteristic