Nonlinear Dynamics in the Resonance Lineshape of NbN Superconducting Resonators

In this work we report on unusual nonlinear dynamics measured in the resonance response of NbN superconducting microwave resonators. The nonlinear dynamics, occurring at relatively low input powers (2-4 orders of magnitude lower than Nb), and which include among others, jumps in the resonance lineshape, hysteresis loops changing direction and resonance frequency shift, are measured herein using varying input power, applied magnetic field, white noise and rapid frequency sweeps. Based on these measurement results, we consider a hypothesis according to which local heating of weak links forming at the boundaries of the NbN grains are responsible for the observed behavior, and we show that most of the experimental results are qualitatively consistent with such hypothesis.Comment: Updated version (of cond-mat/0504582), 16 figure

Limitations of RF field by thermal breakdown in superconducting niobium cavity

The thermal breakdown is unacceptable for high power use of superconducting RF cavities. Limitations of RF field both in He I and He II baths were estimated and discussed on C-band TE011 mode niobium cavities. Calculations were performed by a simulation program under the different assumptions of Kapitza resistance, thermal conductivity and wall thickness, taking lateral heat flow and curvature of the wall into account. (8 refs)