Pulsed electron heating of atmospheric pressure air glow discharges

By applying electric field pulses with duration small compared to the time constant for glow-to-arc transition it is possible to increase the electron energy in high pressure glow discharges considerably over the steady state value. Repetitive pulsed operation allows us to generate plasmas with high average electron density at lower energy cost than with DC heating only. Measurements of the dynamics of the plasma column after pulse application show that the plasma diameter approaches a steady-state value after initial expansion, which is approximately half the DC plasma diameter. As a first step towards repetitive pulsed electric field operation, required to obtain a semi-DC plasma with high average electron density we have measured the temporal development of the voltage across the plasma for two subsequent pulses. The dual pulse generator, built for this purpose, utilizes two, 10 /spl Omega/ striplines with high pressure spark gap as switches, which deliver two subsequent pulses directly to the load. The trigger pulses for the two switches can be adjusted in time between 1 /spl mu/s and 10 ms. Pulse amplitudes of 15 kV have been reached, but amplitudes of up to 50 kV seem to be possible. Experiments with the dual pulse system provide information on the repetition rate required to sustain a certain average electron density. Operation in atmospheric pressure air with applied electric fields of 20 kV/cm and 10 ns duration allowed us to increase the electron density for a time of 2.3 /spl mu/s to such values that the discharge voltage stayed below 30 V. Continuous operation in this discharge state would consequently require repetition rates of 450 kHz. Higher pulsed electric field operation would allow us to reduce the repetition rate.