Production of wall-hugging fast ionization waves for boundary layer control

In order to apply the Lorentz force to boundary layer with low Joule heating, sufficient electrical conductivity of about 1 S/m is required in supersonic air flow. In this research, production of Fast Ionization Waves (FIWs) Discharge in supersonic flow has been studied. The FIWs discharge has attractive features, such as feasibility of efficient ionization, flexible electrode location. When steep-rise high voltage pulse was applied to a hot electrode, the FIWs were produced on the discharge cell. Therefore, pulse power supply with three-stage Magnetic Pulse Compression (MPC) was designed and built up to generate the FIWs. The output peak voltage was (+32) kV or (-32) kV with the 50 ns rise-time, and it was possible to operate the pulse power supply up to f = 3 kHz repetition rate. A hot-electrode made of thin cupper tape was exposed in M=3 supersonic test section. To control the ionization volume, in this research, ground tape was pasted on the outside of the test section wall where the boundary layer developed and the hot-electrode was installed. Two capacitive probes, which could detect electrically-charged FIWs' front propagation and potential amplitude, were embedded in the wall made of acrylic plastic. The FIWs front velocity and reduced electric field were estimated with the two capacitive probes. The charged wave front were observed in M=3 supersonic flow in the both cases of operating positive and negative repetitive pulse discharge. The wave propagation speed was 0.5 cm/ns, when positive 32 kV pulse was applied to electrode under 1 kHz repetition rate. The reduced electric field was estimated from the two capacitive probe was 480 V/cm · torr.