Rapid formation of distributed plasma discharges using X-band microwaves

Summary form only given. Observations of rapidly formed (<;50-300 ns) distributed plasma discharges using X-band microwaves in neon with 1 mTorr residual air are presented. A stainless steel cylindrical discharge test chamber, which is enclosed with polycarbonate windows on both ends, is used to observe microwave breakdown in neon gas from 10 to 760 torr. The chamber is illuminated by the output of 25 kW, 0.8 μs pulse-width, 9.382 GHz magnetron through an X-band waveguide pressed against the polycarbonate window. Measured incident, reflected, and transmitted microwave power to a moveable monopole antenna located beyond the discharge chamber are used to detect the discharge 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. Additionally, an ICCD provides fast (<;50 ns) time-scale optical images of the plasma size, revealing the plasma formation and decay processes. An optical emission spectrum experiment where a small amount of nitrogen is added allows one to determine the gas temperature of the Ne plasma. Mixers are used to compare both the amplitude and phase of the reflected signals before and after 90 degrees shift. Together with a plasma modeling code, plasma parameters such as plasma density, collision frequency and electron temperature are estimated.