Interaction between moderately high power microwaves and plasma in corrugated wall waveguides

Local protuberances in negatively biased probe current (NBPC) after the incidence of moderately high power microwave pulses in a plasma-filled corrugated waveguide are observed. The aim of the present experiment is a fundamental study in the research of high power plasma-filled backward wave oscillators. Protuberances in NBPC profile and the peaks of standing waves of the RF electric field are observed always at the identical axial positions where the radius of the corrugated wall is the minimum. The electron energy distribution after the incidence of the microwave approaches the Druyvesteyn distribution rather than conventional Maxwellian distribution that is observed before microwave incidence. The protuberances in NBPC are found to consist of a uniform increase in electron temperature and of a localized rise in plasma density that is calculated from ion saturation currents. Physical reasons for the observations are discussed in some detail