Effect of Cavity Magnetic Field Detuning on Gyroklystron Performance Characteristics

The uniform longitudinal magnetic field plays a major role in gyroklystron operation, as it maintains the optimal detuning between the radio frequency (RF) fields and the electron beam, enabling an efficient energy extraction mechanism. However, achieving and maintaining a highly uniform magnetic field throughout the RF interaction structure is quite difficult. Magnet design limitations, manufacturing tolerances, alignment issues, and many other unknowns in gyroklystron theory and design can all contribute to magnetic field nonuniformities. Even small nonuniformities in the magnetic field can change substantially the characteristics of the device performance due to the nonoptimal detuning behavior. In this article, an analytical approach based on nonlinear theory has been developed to investigate the effects of cavity magnetic field detuning on the performance of a two-cavity gyroklystron amplifier. The analytical results from the developed analysis are numerically validated for the optimal detuning case against the results of an experimental, two-cavity 35 GHz fundamental harmonic gyroklystron amplifier, as reported in the literature. Subsequently, the analysis is extended to study the impact of unintentional cavity magnetic field detuning on gyroklystron performance. It is found that the unintentional magnetic field detuning in both cavities (input and output) deteriorates the performance characteristics like efficiency, output power, gain, and bandwidth of the gyroklystron. However, the device’s −3 dB bandwidth is found more sensitive to cavity magnetic detuning. The results further demonstrate that the device performance exhibits a greater sensitivity to detuning of the magnetic field in the output cavity than to that in the input cavity.