Frequency Control of a Klystron-Type Relativistic Cerenkov Generator

A klystron-type relativistic Cerenkov generator, which combines the frequency and phase control properties associated with an X-band overmoded relativistic klystron amplifiers with the high-power and high-efficiency associated with a klystron-like relativistic backward wave oscillator, is presented. After the beam current is modulated by the input cavity and buncher cavity, it achieves a large enough modulation depth to induce the produced microwave frequency of the backward wave output section. Moreover, the lossy materials inserted in the device can isolate the input cavity, buncher cavity, and backward wave output section effectively, and thus prevent the generated microwave from locking the input signal. Particle-in-cell simulations show that for a 1 MW injected microwave with a frequency of 9.30 GHz, the generated microwave power is 2.8 GW, and the beam-wave interaction efficiency is 45%. As the injected power increases from 100 kW to 2 MW, the frequency control width extends from 20 to 125 MHz.