Demonstration of Efficiency Enhancement in a High-Power Backward-Wave Oscillator by Plasma Injection

An experimental demonstration of a strong enhancement of the interaction efficiency in a high-power relativistic backward-wave oscillator when plasma is injected is presented. Controlled plasma injection enhances the interaction efficiency over the vacuum case by a factor of up to 8 to a value of about 40%. The enhanced interaction is attributed to induced scattering of the electromagnetic radiation of electrons in an electrostatic field produced by the background plasma and a beam space-charge wave in the corrugated interaction region.