Investigation on pulse-shortening of S-band, long pulse, four-cavity, high power relativistic klystron amplifier

In order to improve the power and gain of a long-pulse relativistic klystron amplifier (RKA), the simulation and experimental studies of an S-band RKA driven by long pulse intense relativistic electron beams (IREBs) were carried out. We investigated the phenomena of self-excitation and pulse shortening, their roots, and the suppression measures in the process of IREB modulation and microwave extraction. The research results show that the reflection of electrons and the transmission of high order modes in the drifting tube, which are excited at the output cavity, are the main origins of the output microwave pulse-shortening. By employing cavities with different working modes, adding a graphite ring in the drifting tube as a microwave absorber and an electron blocker, the problem of self-excitation and pulse shortening is significantly mitigated. The output microwave with a peak power of 1.73 GW and a pulse width of 110 ns was obtained from the four-cavity RKA driven by an annular beam of voltage 850 kV, current 7.6 kA, and pulse width 190 ns; the gain is 51 dB; and the phase jitter range is about +/- 20 degrees. Published under license by AIP Publishing.