A computer model

Summary form only given, as follows. Experiments have demonstrated that a plasma filling of a microwave tube can enhance the efficiency by a factor of 8. The plasma filling can neutralize space charge, cause electron beam focusing by ion space charge, and favourably modify the effective dielectric constant. However, the plasma ions can also exhibit an instability, causing frequency and amplitude jitter, and even termination of the electron beam. However, observations on a steady-state, gas-filled Orbitron Maser have demonstrated stable operation. A suggested stabilization effect is that ions are ejected continuously radically from the system before an instability can grow. Analytical models based on the simplified Budker-Buneman instability show that a slow transverse ion flush greatly reduces the growth rate of the instability. In this report, we present computations based on the computer code MAGIC that support the analytical calculations for the Budker-Buneman model. More advanced calculations for a prototype microwave tube are now in progress.