Systematic Trends for the Medium Field Q-Slope

The medium field Q-slope for Nb cavities has been studied in the past as a thermal feedback effect combined with the nonlinear BCS surface resistance due to currentinduced RF pair-breaking. We are systematically exploring the behavior of the medium field Q-slope with various cavity parameters such as wall thickness, residual resistance, bath temperature, Kapitza conductance, RF frequency, RRR, and phonon mean free path. We study cases involving only the standard (linear) BCS resistance as well as those including the nonlinear BCS resistance. The systematic comparison suggests specific experiments to determine the role of the nonlinear contribution.