Magnetohydrodynamic Power Extraction from Cold Hypersonic Airflows with External Ionizers

Abstract

A novel concept of hypersonic cold-air magnetohydrodynamics (MHD) power generators with ionization by electron beams is analyzed. Electron beams are shown to allow control and stable operation of MHD channels in cold high-speed flows. To avoid excessive energy cost of ionization and damage to beam-injection foils, electron beam current densities should be restricted to a few milliamperes per square centimeter. This reduces the conductivity in electron beam sustained MHD channels compared with that in conventional MHD generators, restricting performance and calling for very strong magnetic fields and high Hall parameters. The high Hall parameters cause ion slip and near-anode phenomena to become first-order issues. Example one-dimensional calculations of hypersonic power generator performance appear to be promising. Possible problems that could be caused by hypersonic boundary layers and electrode sheaths, including anode sheath instability and ways to avoid it, are also discussed.