Large-signal characteristics of a wide-band dielectric-loaded gyro-TWT amplifier

The bandwidth of a gyrotron traveling wave amplifier (gyro-TWT) has been significantly increased by partially filling the interaction waveguide with dielectric to reduce the circuit's dispersion, The proof-of-principle experiment was designed for X-band, and employs the fundamental mode of rectangular waveguide loaded with dielectric slabs along the narrow sidewalls, The amplifier yields a peak output power of 55 kW with 11% efficiency, 27 db saturated gain, and an unprecedented untapered gyro-TWT constant-drive bandwidth of 11% and saturated bandwidth exceeding 14%, The single-stage amplifier is completely zero-drive stable, The 95-kV 5-A electron beam was produced by a single-anode magnetron injection gun with upsilon(perpendicular to)/upsilon(z) = 0.6, as determined by the EGUN code, and Delta upsilon(z)/upsilon(z) = 4%, determined as the best fit to the gyro-TWT large-signal simulation data, Simulation studies predict that by lowering the velocity spread to Delta upsilon(z)/upsilon(z) = 2%, the amplifier performance will be further enhanced to a constant-drive bandwidth of 20% with 15% efficiency.