An Improved Reference Cavity Design for Frequency Tracking of RF Accelerating Structures

A simple automatic frequency control system providing accurate frequency tracking has been built. The system makes use of the temperature difference between inlet and outlet accelerator coolant, establishing this difference between two regions of appropriately shaped reference cavities. Two re-entrant 3 GHz cavities were used to frequency lock a 1.8 MW magnetron to a 1.6 m long standing wave pulsed electron accelerator. Tests show that for a 30??C change in input water temperature and/or a variation of average power between 0.02 and 2.0 kW, the desired frequency tracking is obtained.