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 and Ne(Ar) mixture gases 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 noble gases including Penning discharge Ne(Ar) and Ne(Kr) mixes 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. Evaluations of reflection and transmission caused by plasma and absorption to sustain plasma under different conditions have been made. Additionally, an ICCD camera provides fast (<;50 ns) time-scale optical images of the plasma size, revealing the plasma formation and decay processes. Optical emission spectroscopy measurements provide plasma breakdown characteristics including temporal (t<;50 ns) measurements of gas and electron temperatures and plasma density. Mixers are used to compare both the amplitude and phase of the reflected signals. These measurements, together with a plasma modeling code, allow estimates for plasma density, collision frequency and electron temperature to be determined.