Suppression of self-oscillation in high gain relativistic klystron amplifier by RF lossy material

In the high gain relativistic klystron amplifier, higher mode self-oscillation seriously degrades klystron performance and causes pulse shortening. The mechanism of higher mode excitation is explored in the PIC simulation, and RF lossy material is introduced to suppress higher mode self-oscillation. The relations of the attenuation characteristics with thickness, electric conductivity and length of the lossy material are studied. The cold test of the lossy material is performed. The attenuation of the lossy material is about 11.25 dB which fulfills the requirement of the suppression of self-oscillation, and can be used in the high gain relativistic klystron amplifier.