Simulation of pulse shortening in a relativistic klystron oscillator

Summary form only given. The relativistic klystron is a strong candidate for a high power microwave source for a number of applications, including accelerators and electronic warfare. In this work, we simulate a high power, high perveance relativistic klystron oscillator using XOOPIC (a 2d, electromagnetic PIC-MCC code) and ICEPIC (a parallel, 3d, electromagnetic PIC code). The experimental klystron operates as an injection-locked oscillator at 1.25-1.35 GHz, with up to 1 GW rms output power for a 100 ns pulse. The beam voltage is 500 kV, with current of 10 kA, and a beam pulse length of 300 ns. Of particular interest for this device is the shortening of the rf pulse compared to the current pulse. Two mechanisms for rf pulse shorting are examined: plasma formation near the extractor gap, and diode impedance collapse.