Coherent Combination of Power in Space With Two X-Band Gigawatt Coaxial Multi-Beam Relativistic Klystron Amplifiers

The power capacity of an individual high power microwave (HPM) generator is severely limited by internal electric field breakdown, and the problem becomes more serious for long pulse and high frequency bands. One of the promising solutions to overcome this limitation is coherent combination of power in space. To realize coherent combination of power in space, the HPM generators must operate at the same frequency and stable phase differences. We presented an improved X-band gigawatt coaxial multi-beam relativistic klystron amplifier (CMB-RKA) with high phase stability. Two double gap buncher cavities were designed to improve the beam wave interaction efficiency, and decrease the distance for the modulated intense relativistic electron beam to reach its maximum, which significantly decrease the phase jitter due to the fluctuation of electron beam voltage and improve the phase stability of the CMB-RKA. Experimentally, the two X-band gigawatt CMB-RKA demonstrated the capability of coherent combination of power in space, typically of the combined efficiency of about 95% with the combined pulse width of 150 ns.