Nirmol Kumar Podder

Shockwave Acceleration and Attenuation in Glow Discharge Argon Plasma

Experimental investigations of the shockwave propagation in the direction parallel to the electric field in low-pressure longitudinal glow discharge argon plasmas are performed by the simultaneous multipoint laser deflection technique. In the newly developed shock tube at Troy University, Mach 1.5-2.2 shockwaves are produced by a fast capacitor discharge (quarter period tau1/4 = 1.4 mus ). In this paper, the shock propagation measurements are extended to the low pressure limit down to 3.6 torr while confirming the earlier measurements performed at gas pressures 15 torr and above. The shockwaves are launched through a plasma medium inside the shock tube, where the deflections of the laser beams are recorded on a fast oscilloscope. An average shockwave velocity in the plasma is determined from the time history of the laser deflection signals. The shockwave speed and the broadening of the laser deflection signals in the plasma are found to be dependent on the plasma discharge current. Shockwave speeds increase by 18% for the plasma at 3.6 torr over a range of plasma discharge current I = 0-150 mA and by 46% for the plasma at 15 torr over I = 7-150 mA. In addition, shockwave amplitudes are attenuated in the plasma and show linear dependence on the shockwave speed or Mach number.

Development and Diagnostic of a Localized Microwave/rf Plasma for Shock Wave Propagation Study

The current research effort extends the previous shock wave propagation measurements into localized microwave/rf plasmas with a greater ionization fraction compared to glow discharges. The electrodeless microwave configuration is suited for the high altitude supersonic flight application of plasmas. The research has a strong high-speed aerodynamics component. The decrease in shock strength in plasma presents a means of aerodynamic drag reduction, and thus improving supersonic flight characteristics by modifying the gas fluid through which the flight occurs. If an electronically conducting medium could be introduced upstream of a vehicles bow shock wave, this will have a potential for improved high speed flight.