Nonlinear Analysis of a Gyroklystron Amplifier with Misaligned Electron Beam

Abstract

In this paper, a nonlinear single mode analysis has been developed for studying the beam-wave interaction behavior of gyroklystron amplifiers. The normalized parameters: field amplitude, length and detuning parameter, are optimized for the efficient device operation through the contour plots, and have been extended here in terms of a mathematical model. Further, in the present work, the momentum and phase for each cavity of the gyroklystron amplifier have been obtained by considering the actual device parameters instead of arbitrarily chosen parameters to estimate the efficiency in individual cavities to get the overall efficiency of the device. The bandwidth of the device is thus obtained by estimating the variations of RF power output with frequency. Moreover, the effects of practical problems of the electron beam misalignment and axial velocity spread on the performance of gyroklystron amplifier have also been analyzed in the presented model. It has been found that the RF output power is more sensitive in comparison to the device bandwidth to the electron beam misalignment. To validate the developed mathematical model, an experimental 35 GHz four-cavity gyroklystron amplifier, reported in the literature, has been selected. The results from the nonlinear formulation predicted a stable RF output power of 180 kW at 34.9 GHz, with ~56 dB gain, 26 % efficiency and a bandwidth of 0.54 % for a 72 kV, 9.6 A gyrating electron beam. The analytically obtained values of RF output power and gain are found to be in agreement with the experimental results within ~5 %. The analytical result has also been validated through the 3D PIC simulation using a commercially available code within ~5 %.