Energy-efficient generation of nonequilibrium plasmas and their applications to hypersonic MHD systems
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A novel concept of hypersonic cold-air MHD power generators is reviewed. lonization of the cold air is shown to be a critical issue, determining overall design, geometry, operating conditions, and performance envelope. Electron beams and high-voltage repetitive pulses are shown to represent most efficient methods of ionization. The requirement that the energy cost of ionization be lower than the extracted electric power restricts conductivity and calls for very strong magnetic fields and high Hall parameters, making ion slip and near-anode processes first-order issues. Calculations of hypersonic power generators for flight Mach numbers between 4 and 10 and altitudes of 15-40 km are quite promising: several megawatts of electric power could be generated, while spending only a few hundred kilowatts of that power on sustaining ionization. External MHD devices with ionization by electron beams are shown to be promising for scramjet inlet control at off-design Mach numbers. The self-powered MHD system can bring compression shocks to the cowl lip at Mach numbers higher than the design one, while generating large amounts of electric power on board. High values of Hall electric field are discussed as an important issue, potentially resulting in arcing between electrode segments. lonization enhancement by change of recombination mechanism with addition of metallic vapor to the flow is discussed, and the minimum seed concentration is estimated. 2001 by Princeton University. Published by the American Institute of Aeronautics and Astronautics, Inc.
