ABSOLUTE INSTABILITY FOR ENHANCED RADIATION FROM A HIGH-POWER PLASMA-FILLED BACKWARD-WAVE OSCILLATOR

The linear theory of electromagnetic radiation from a backward-wave oscillator with a plasma-filled, sinusoidally corrugated waveguide driven by a relativistic electron beam has been derived and analyzed numerically. The presence of plasma can cause a substantial increase in the spatial growth rate of the absolute instability. For high plamsa densities, however, the absolute instability is suppressed and only the convective instability remains. The predicted radiation enhancement can be attributed to a decrease in the group velocity of the backward wave in the presence of a plasma. © 1990 The American Physical Society.