Microphonics detuning in the 500 MHz superconducting CESR cavities

The RF system of the Cornell Electron Storage Ring (CESR) consists of four superconducting (s.c.) 500 MHz cavities. For a charm-tau upgrade (CESR-c) we plan to drive two cavities by one klystron and to operate some cavities in passive mode. During the previous high energy run the RF system performance was not significantly affected by microphonic cavity detuning, since the cavities were operated under strong beam loading with a low loaded quality factor of 2 · 10⁵. However, in low energy CESR-c operation with increased loaded Q-factor the RF system becomes less tolerant to microphonics, especially when two cavities are driven by one klystron. In order to address this potential problem we have studied microphonics in the CESR cavities in detail. Significant improvements have been achieved by reducing major contributions to the detuning. For further improvements we plan to study the performance of an active microphonics compensation scheme, which is based on a fast piezoelectric-driven frequency tuner.