The Effects of Electrons on Superconducting Cavities in the GHz Region

In superconducting cavities in the GHz region several field-dependent effects have been observed. Besides qualitatively well-understood effects due to H2 such as radiation pressure or heating one encounters also strange effects which could be explained by pre-breakdown field emission or by high-order multipactoring. The presence of electrons limits the power fed into the cavity and may cause a strong inductive loading of the cavity, permitting a pulling of the oscillating frequency by more than 10 kHz above the smallfield resonant frequency. Since this phenomenon could seriously hamper a frequency-tuning servo-system, we carried out a detailed study on superconducting cavities, the results of which are presented in this paper.