The design procedure for a stable high power gyro-TWT

A design procedure has been developed which will result in stable operation of a high power gyrotron traveling wave tube amplifier(gyro-TWT). The design tools consist of an analytical linear theory and a nonlinear theory.; The linear theory and the nonlinear theory verify each other in the linear interaction region. The linear theory predicts the start oscillation conditions, the linear gain, and launching loss, which can provide guide lines for the design of a stable gyro-TWT. The nonlinear simulation code analyzes the nonlinear performance. There is a threshold current for the forward wave absolute instability to take place, and for each operating current there is a start oscillation length for the backward wave oscillation to grow. By searching the operating parameter space, the performance can be optimized subject to these two limitations. The operation of a stable gyro-TWT with high output power at high efficiency and sufficient gain can be realized by using a multi-stage amplifier design, where the operating current is less than the start oscillation current of the absolute instability of the operating mode and the length of a single stage is shorter than the start oscillation length of the BWO interactions.; The linear and nonlinear theories provide some physical insight into the gyro-TWT interaction. The common intuitive estimation of a launching loss of 9.54 dB has been found not sufficient to give a reasonable approximation. The linear theory can estimate the effective bandwidth of the CARM interaction. A new bunching mechanism has been discovered in a two stage gyro-TWT, which results from the strong modulation of the electrons in the first section. The saturated bandwidth is narrower than in a single stage gyro-TWT. The performance of a two-stage gyro-TWT is more sensitive to the velocity spread of the electrons.; The comparison between the simulation and experimental results gives a fair agreement in the linear gain and bandwidth, but a 35% discrepancy is found in the saturated output power. (Abstract shortened with permission of author.)...