High-current relativistic klystron amplifier development for microsecond pulse lengths

The performance of the Friedman-type high-current relativistic klystron amplifier (RKA) is being extended to the microsecond regime while attempting to achieve the gigawatt-level peak power capability that has been characteristic of the RKA at shorter pulse lengths. Currently the electron beam power into the device is about 1 GW in microsecond duration pulses, with an effort underway to increase the beam power to 2.5 GW. To date the device has yielded an RF-modulated electron beam power of 350 MW, with up to 50 MW coupled into waveguide. Several aspects of RKA operation under investigation that affect RKA beam bunching efficiency and amplifier gain include cavity tuning, beam diameter, beam current, and input RF drive power, and the development of an output coupler that efficiently couples the microwave power from the low-impedance beam into the rectangular waveguide operating in the dominant mode. Current results from experimental testing and code modeling are presented.<>