Compact, Stable, Repetitive GW-Level S-Band Multibeam Relativistic Klystron Amplifier Operating Over a Longer Period in a Lower Magnetic Field

The design, based on theory, simulation, and cold as well as hot tests, is proposed for a compact GW-level multibeam relativistic klystron amplifier (MB-RKA) with a low beam confining magnetic field in the ${S}$ -band, which can operate repeatedly and stably up to 8 min. For this purpose, graphene cathodes and a microchannel water cooling system were used. For the sake of compactness, the input Section of the MB-RKA was taken as a cylindrical conformal sectorial waveguide and the output Section as an inner cylindrical coaxial waveguide. The experiments were performed with a magnetic field of 0.39 T. In the single-pulse operation, the output power, pulsewidth, gain, and efficiency of the device were experimentally found as 1.047 GW, 68 ns, 56 dB, and 37% respectively, when the beam voltage, beam current, and injected power were taken as 530 kV, 5.30 kA, and 2.40 kW, respectively. In the multipulse operation at a pulse repetition rate of 20 Hz, over a period of 8 min, the MB-RKA experimentally delivered the mean output power of 0.889 GW of 42-ns pulsewidth, taking the mean beam voltage and current as 551 kV and 5.14 kA, respectively.