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 p/sub /spl perp////spl upsi//sub z/=0.6, as determined by the EGUN code, and /spl Delta//spl upsi//sub z///spl upsi//sub 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 /spl Delta//spl upsi//sub z///spl upsi//sub z/=2%, the amplifier performance will be further enhanced to a constant-drive bandwidth of 20% with 15% efficiency.