Optimization of the efficiency in gyrotron backward wave oscillator model via tapered axial magnetic field

Summary Form only given, as follows. The nonlinear evolution of the gyrotron backward wave oscillator (gyro-BWO) has been investigated numerically in the presence of a tapered axial magnetic field. The set of coupled nonlinear differential equations that govern the self-consistent evolution of the TE modes and the trajectories of an ensemble of electrons in a gyrotron have been solved subject to boundary conditions for both the usual BWO (power extracted at the input end) and the reflection-type BWO (power extracted at the input end) and the reflection-type BWO (power extracted in the forward direction) configurations. The space-charge effects were neglected. The calculated saturation efficiency is about 10-15% in the K/sub a/-band with rectangular TE/sub 10/ modes and near 104 GHz with cylindrical TE/sub 10/ modes. However, the efficiency can be greatly enhanced (>30%) by tapering the magnetic field. The frequency of the oscillator can be magnetically tuned over a 15% bandwidth. Beam thermal effects have also been investigated.<>