  Plasma processing of superconducting radio frequency (SRF) cavities has shown
an improvement in accelerating gradient by reducing the radiation due to field
emission and multipacting. Plasma processing is a common technique where the
free oxygen produced by the plasma breaks down and removes hydrocarbons from
surfaces. This increases the work function and reduces the secondary emission
coefficient. The hydrocarbon fragments of H2, CO, CO2, and H2O are removed from
the system with the process gas which is flowing through the system. Here, we
present COMSOL for the first time to simulate the plasma processing of an SRF
cavity. In this work, we use Jefferson Lab's C75 SRF cavities design as our
case study. Using simulation, we predict the condition of plasma ignition
inside the SRF cavity. The simulation provides information about the optimal rf
coupling to the cavity, mode for plasma ignition, choice of gas concentration,
power, and pressure.
