1 Efficient Ionization Investigation for Flow Control and Energy Extraction

Non-equilibrium ionization of air by non-thermal means is explored for hypersonic vehicle applications. The method selected for evaluation generates a weakly ionized plasma using pulsed-nanosecond, high-voltage discharges sustained by a lower DC voltage. These discharges promise to provide a means of energizing and sustaining electrons in the air while maintaining a nearly constant ion/neutral molecule temperature. This paper explores the use of short ~5 nanosecond (nsec), high-voltage ~12-22 kV, repetitive (40-100 kHz) discharges in generating a weakly ionized gas sustained by a 1 kV DC voltage in dry air at pressures from 10-80 Torr. Demonstrated lifetimes of the sustainer discharge current ~10-25 µsec are over three orders of magnitude longer than the 5 nsec pulse that generates the electrons. This life is adequate for many high speed flows, enabling the possibility of exploiting weakly-ionized plasma phenomena in flow-fields such as those in hypersonic inlets, combustors, and nozzles. Results to date are obtained in a volume of plasma between electrodes in a bell jar. The buildup and decay of the visible emission from the pulser excited air is photographed on an ICCD camera with nanosecond resolution and the time constants for visible emission decay are observed to be between 10-15 nsec decreasing as pressure increases. The application of the sustainer voltage does not change the visible emission decay time constant. Energy consumption as indicated by power output from the power supplies is 194-669 W depending on pulse repetition rate. I