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 up to 20 MV. Each of these quarter-wave cavities will be powered at a frequency of 106.08 MHz to a maximum field gradient of 6 MV/m. A test area was built to clean and test each cavity before installation. With unloaded cavity Q's of ~10 9 , the RF control system of these superconducting cavities is based on self-excited feedback loop, with the self-excited frequency stabilized by an internal analogue Phase-Locked Loop, capable of operating in both CW and pulse mode. A digital phase/frequency detector and a quadrature combiner are used to provide phase locking to an external frequency reference. The demodulated amplitude, phase and frequency are feedback regulated with digital signal processors. This paper describes the RF control system and the experience in operating this system with a prototype cavity.
A Digital Signal Processor-based control system has been designed and tested for use with the ISAC RFQ accelerator. This system uses a direct digital synthesizer and phase-locked loop to generate the 35MHz nominal cavity frequency. One DSP provides both in-phase and quadrature control for the system. A second DSP operates the cavity tuning mechanism. A reference signal with digital controlled phase shift is output for use in the upstream cavity in the beam path, an 11.66 MHz prebuncher. The system incorporates spark and high Voltage Standing Wave Ratio detection and protection. It also includes operator-controlled hardware limiting, and visual feedback of operating conditions. The complete system including low-level RF components is housed in a VXI rack. Turn-key operation is achieved via a supervisory control, which consists of a Windowsbased server. This server broadcasts system status using User Datagrams, and listens on control commands via TCP. Network-aware database objects interpret these messages to provide control and display of the system operating parameters.
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