High power X-band TWT amplifiers

Summary form only given, as follows. Our recent research into multi-stage X-Band TWT´s producing output powers of 100-200 MW has shown that it is essential to minimize the reflections in each stage of the amplifier in order to avoid sideband development. These reflections also cause fluctuations in the RF output power envelope. Following extensive MAGIC code simulations we have designed tapers that adiabatically increase the iris diameter in the output sections of the amplifier to provide a smooth, broad-band transition from the slow-wave structure to cylindrical waveguide. We report results, extracting in the TM/sub 01/ mode, showing smooth output pulses in the range 30-50 MW, with no evidence of sidebands. A second approach seeks to isolate the first amplifier stage with a drift tube beyond cutoff. The second stage and output section are quasi-periodic structures designed to minimize reflections, and allow the radial or longitudinal RF power extraction to be distributed over an extended region. The first stage of this system has been developed and initial operation results using an 0.8-1.0 MV, 0.5-1.0 kA, 50 ns cylindrical beam will be reported.