External control of plasmas for high-speed aerodynamics

The paper gives an overview of research at Princeton University on generation and control of plasmas that could be applied to high-speed aerodynamics, and on mechanisms of plasma effects on shock waves. Theoretical and computational results show that experimentally observed changes in shock structure and velocity in weakly ionized gases are explained by thermal mechanisms, and non-one-dimensionality (transverse gradients, shock curvature, vorticity, etc.) plays a critical role. A direct experimental proof of the thermal mechanism was provided by pulsing a glow discharge. With several hundred microseconds time delay between starting the discharge and shock launch, electric current, field, and the discharge luminosity reach their steady-state values, while the temperature is still cold. In this regime, laser Schlieren signals are virtually identical to those without the discharge, differing dramatically from the signals in discharges with fully established temperature profiles. Vibrational relaxation effects are indicated as the most probable mechanism of “anomalous” shock stand-off distances observed in plasma ballistic experiments. The paper discusses experimental results on laser triggering and guiding of microwave streamer discharges and possible applications in aerodynamics. Results of modeling of plasmas generated by electron beams are presented. E-beams are shown to be promising as a plasma generation technique for external aerodynamics (shock control, steering, etc.) - both by themselves and in conjunction with microwaves. E-beam plasmas can also be useful as an efficient nonequilibrium ionization method in hypersonic MHD channels.