Rf Control System for Isac Ii Superconducting Cavities

The first phase of the ISAC II project consists of the acceleration of radioactive ions by 20 superconducting DTL's with a total effective voltage of ~20MV. Each of these cavities will be powered at a frequency of 106.08 MHz to a maximum field gradient of 6 MV/m. With unloaded cavity Q's of ~10, the RF control system for these superconducting cavities is based on a self-excited feedback loop. The self-excited frequency is stabilized by an internal analogue Phase-Locked Loop. A digital phase/frequency discriminator and a quadrature combiner are used to provide phase locking to an external frequency reference to allow all the cavities to run synchronously. The demodulated amplitude, phase, and frequency are feedback regulated with digital signal processors. This paper describes the RF control system and the experience gained in operating this system with a single test cavity.