High-Power Harmonic Gyro-TWT's-Part 11: Nonlinear Theory and Design

Abstruct- Based upon an analytical study of the stability problems of gyrotron traveling wave amplifiers (gyro-TWT’s), the design of an extremely high power second-harmonic gyroTWT has been developed and then evaluated and optimized with a self-consistent nonlinear numerical simulation code. Although an axis-encircling electron beam yields stronger interaction, a design based on the more common magnetron injection gun (MIG) type beam is presented. Using a 100 kV, 25 A MIG beam with a = 1 and an axial velocity spread of 5%, nonlinear selfconsistent analysis of a three-stage second-harmonic gyro-TWT amplifier predicts a peak output power of 533 kW, peak efficiency of 21.3% and a 7.4% saturated bandwidth, which verifies the assessments of analytical theory that a stable harmonic gyroTWT can generate power levels an order of magnitude higher than those possible from a fundamental gyro-TWT. It is shown that the positioning of the electron beam is very important. A multistage structure is employed in the design to recover the loss in gain resulting from the shortening of the interaction sections to ensure stability.