RETRACTED: Investigation on S-band long pulse four-cavity relativistic klystron amplifier (Retracted Article)

In order to improve the power and gain of a long-pulse relativistic klystron amplifier (RKA), the design and experimental study of an S-band RKA were developed. We investigated the phenomena of self-excitation as well as the suppression measures. The research results show that the reflection of electrons and transmission of high mode in the drifting tube, which is excited at the output cavity, are the main causes of self-oscillation. By employing cavities with uneven modes, adding a ring in the drifting tube as a microwave absorber and electron beam blocker, the problem of self-excitation is significantly mitigated. Output microwave with a peak power of 1.68 GW and a pulse width of 110 ns was obtained by using an annular beam of 830 kV/7.2 kA/pulse width 190 ns, the gain is 51 dB.