A Relativistic Coaxial Klystron Amplifier for Phase-Locked High Power Microwave Generation

We present a high-power and high-gain coaxial klystron amplifier featuring a two-stage cascaded double-gap bunching cavity design, capable of producing phase-locked radiation at 2 GW level in X-band. The cascaded bunching cavities have been optimized to achieve high fundamental harmonic current modulation of intense electron beam. According to the particle-in-cell simulations, the amplifier generates a highpower microwave output of 2.5 GW at a frequency of 9.375 GHz. This is achieved using a $740 \text{kV}, 9.1 \text{kA}$ electron beam with a 50 kW seed microwave. The proposed high power amplifier demonstrates an efficiency of 37 % and a gain of up to 47 dB. Additionally, the output microwave phase remains locked when the amplifier reaches saturation, which lays solid foundation for future coherent combining of multiple sources.