Non-equilibrium ionization techniques for MHD power extraction in high-speed flows

In hypersonic applications and MHD power generation and flow control, conventional high temperature seeded MHD methods are very problematic for flight speeds of less than Mach 12, because the temperature is insufficient for natural ionization at those Mach numbers, but non-thermal ionization is an attractive alternative. In addition to requiring efficient ionization, non-thermal MHD power extraction will require strong magnetic fields to compensate for the relatively low conductivity. An experimental facility has been constructed to demonstrate nonequilibrium ionization for MHD power extraction at Mach 3. The facility includes a 6 Tesla superconducting magnet and access ports for the electrodes and ionizer. In this investigation, various nonequilibrium ionization techniques were explored. For the experimental work, ionization technique based on very short high-voltage pulses with very high repetition rate was employed and, for this purpose, a source of multikilovolt (~30 KV) subnanosecond pulses (~2.0 ns) with repetition rate of about 100 KHz was used. Microwave transmission and optical emission diagnostic techniques were developed for use in the facility to provide information on plasma parameters and molecular gas temperatures. In addition to the experimental work, theoretical performance of Faraday- and Hall- type generators with nonequilibrium ionization based on the experimental conditions was estimated in a quasi- 1D approximation.