A method of frequency following for a linac with power feedback

Three factors are found to influence the frequency stability of the magnetron which is the power source of a linac: the change of the modulating voltage, the slow change of the environment temperatures, and the unstable reflection from the accelerating tube with power feedback. A decreasing Q circuit is used to stabilize the modulating voltage. The frequency shift caused by the change of the environment temperature can be decreased by a frequency stabilization system. The frequency change introduced by the unstable reflection can be decreased by an adaptive frequency following controller. When an adaptive control loop is added to the feedback loop of the frequency stabilization system, adaptive frequency following will result. A digital controller which is a single-chip microprocessor is used to perform a rapid frequency stabilization and a slow frequency following. The optimal frequency following is realized by maximizing the area of the superposition envelope at the entrance of the accelerating tube. In order to realize rapid frequency stabilization, a high-speed SCR system with three current converters in sequence is used to drive the stepping motor of the frequency stabilization system