A Microprocessor-Based Feedback System for Phase and Amplitude Stabilization of Superconducting Resonators

A microprocessor-based feedback system has been designed, built and tested to provide phase and amplitude stabilization of a 150 MHz superconducting splitring accelerating resonator for heavy ions. This system has a bandwidth of 400 kHz and can operate with positive feedback as a limiter or with negative feedback locking to an external reference. Direct negative feedback has already been used to stabilize the phase of a split-loop resonator to an accuracy of 0.01 radian at 2 MV/m.1 All of the parameters of the system: gains, phase shifts, level reference, phase reference and frequency of the synthesizer are digitally controlled either manually or by the microprocessor. The advantages of this control system include automatic operation of the accelerator, pre-warning of an eventual breakdown of a resonator, and automatic recovery from such a breakdown.