A relativistic klystron amplifier at high average power

Summary form only given, as follows. A 1.3-GHz relativistic klystron amplifier has been operated at repetition rates of up to 200 Hz, for 200 shots. The electrical driver is the CLIA pulser at Physics International, which is capable of producing bursts of 750-kV, 10-kA, 100-ns-long electron beam pulses at 200-250 Hz. For this experiment, a 5-kA, 500-kV electron beam is generated, which is approximately 80% modulated after two cavities (the input cavity and single idler cavity). The microwave pulses, extracted by a third cavity, are 100-ns long, corresponding to the electrical pulse length of the driver. The power level, as measured in a rectangular waveguide in fundamental mode, is currently limited to 150-MW peak, 2 kW average. An improved extraction scheme has been investigated.