VOLUMETRIC NEAR-FIELD MICROWAVE PLASMA GENERATION

A periodic series of microwave-induced plasmoids is generated using the outgoing wave from a microwave horn and the reflected wave from a nearby on-axis concave reflector. The plasmoids are spaced at halfwavelength separations according to a standing-wave pattern. The plasmoids are enhanced by an “effective focusing” in the near field of the horn (Fresnel region) as a result of a diffractive narrowing. Optical imaging, electron density, and rotational temperature measurements characterize the near field plasma region. Volumetric microwave discharges may have application to combustion ignition in scramjet engines. A. Introduction