Demonstration of efficiency enhancement in a high power backward wave oscillator by plasma injection

A strong enhancement of the interaction efficiency in a high-power relativistic backward wave oscillator when plasma is injected has been demonstrated experimentally. Plasma injection enhances the interaction efficiency by a factor of up to eight to a value of about 40%. Overdriving the device with plasma above a critical density quenches the interaction. It is anticipated that plasma injection will prove beneficial in other high-power microwave and millimeter-wave devices, such as free-electron lasers and gyrotrons. 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. >