Maniscalco, J.T. Koufalis, P.N. Liepe, M. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-TUYAA01 English 359-363 TUYAA01 cavity ion niobium electron SRF Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-TUYAA01 http://jacow.org/srf2017/papers/tuyaa01.pdf Theoretical results offer a potential explanation for the anti-Q-slope, the phenomenon of decreasing microwave surface resistance with increasing radiofrequency electromagnetic field strength. This effect has been observed in niobium doped with impurities, chiefly nitrogen, and has been put to use in the Linac Coherent Light Source II (LCLS-II) accelerator currently under construction. Our work, presented here, finds a strong link between the electron mean free path, the main measure of impurity doping, to the overheating of quasiparticles in the RF penetration layer. This is an important effect that adjusts the magnitude of the theoretical anti-Q-slope by providing a mechanism to counteract it and introduce a surface resistance that increases with field strength. We discuss our findings in a study of niobium cavities doped at high temperature (800-990 °C) as well as new analysis of low-temperature-doped cavities.