The frequency stability of the power source for a feedback LINAC depends on the slow shift

stability and form of power spectrum of the magnetron. The first two factors affect the short-term frequency stability and the last one relates to the long-term frequency stability. The control exactness of the frequency stabilization system can be increased by means of a method in which the area change of output signal from the detector of the frequency discriminator is used to indicate frequency shift and to drive a stepping servo motor. The frequency corresponding to a performance index

i.e. the maximal area of the superposition envelop at the entrance of the accelerating tube

is tracked by the oscillation frequency of the magnetron for improving the long-term frequency stability. In order to eliminate the influence of the modulator when the CPU is running

the CPU can be forced to reset periodically to keep the control function.The frequency stability is 7×10-6.