Theory of quasioptical gyrotrons and gyroklystrons operating at higher harmonics of the cyclotron frequency

A multimode, non-linear, time-dependent formulation of the theory of quasioptical electron cyclotron masers operating at high gyrofrequency harmonics is presented. Linear calculations of the starting current and numerical analyses of the efficiency of the devices are performed. It is shown that with suitable contouring of the DC magnetic field, a stable single mode operation at the second harmonic is possible. To improve the efficiency, an alternative configuration, the quasioptical gyroklystron, is also analysed using single mode and multimode dynamics simulations. The gyroklystron operating at the second harmonic is shown to lead to a significant increase in efficiency (approximately 30%).