Rapid X-band microwave breakdown in Ne

Abstract

Observations of rapidly formed (<;50-400 ns) distributed plasma discharges using X-band microwaves in Neon with 1 mTorr residual air are presented. A stainless steel cylindrical discharge test chamber is used to observe microwave breakdown at 10 to 760 torr pressures. The chamber is enclosed with polycarbonate windows on both ends and has two side ports. The magnetron illuminates the chamber using 25 kW, 9.382 GHz and 0.8 μs pulse-width power through an X-band waveguide pressed against the polycarbonate window. Microwave diodes are used to measure incident, reflected, and transmitted microwave power to a moveable monopole antenna located beyond the discharge chamber. They provide information to determine the discharge reflection and attenuation characteristics as the pressure is varied. Observations of localized transmission power reduction measurements of -20 dB that occur within 50-400 ns caused by the plasma under different conditions have been made. Optical emission spectra experiments allow one to determine the gas temperature of the plasma at different pressures. Microwave mixers are used to compare both the amplitude and phase of the reflected signals in phase and in quadrature (90 degrees) relative to a fixed phase reference signal. Together with a six region 1-D plasma modeling code, the effective plasma density, collision frequency and electron temperature are estimated. An ICCD provides fast (<;50 ns) time-scale optical images to estimate the plasma size, also revealing the plasma formation and decay processes.