Stable Operation of a Repetitively Pulsed X-Band Gigawatt Long Pulse Coaxial Multi-Beam Relativistic Klystron Amplifier

In this letter, the stability of an X band gigawatt coaxial multi-beam relativistic klystron amplifier (CMB-RKA) operating in repetitively pulsed mode was investigated by the particle-in-cell (PIC) simulation and experiments. A four-gap extended-interaction output cavity was optimized to avoid electrons reflection. And a water-cooled electron beams collector which was integrated with the output mode converter was designed to reduce the plasma and secondary electrons. The explosive emission conditions were improved by using the C–C composite material cathode, and the titanium beam-wave interaction structure was used to replace the stainless steel structure. All these factors brought greater stability of the CMB-RKA. In the experiment, the X-band CMB-RKA can operate at a 20 pps repetition rate with duration of 120 seconds, when the output power was about 0.95 GW with pulse width of 160 ns. The long-term stability of the X-band CMB-RKA performances during $10^{{5}}$ pulses was realized, which is driven by a long pulse compact accelerator.