Experimental Studies on Atmospheric Pressure Glow Discharge For Drag Reduction and Microwave Invisibility

Abstract

Absorption and reflection of microwaves from plasma with electron density gradients and reduction of frictional drag force on moving aircrafts are the important issues of atmospheric pressure plasma applications. For these purposes several thermal and non-thermal plasma sources have been developed that work near atmospheric pressure. The characterization of these plasmas has also been done by many researchers using mostly spectroscopic techniques. The Langmuir probe diagnostic, inspite of its theoretical limitation at high collisional regime, has also been reported in many experiments to characterize high-pressure plasmas. We are reporting the comparison of two diagnostic techniques i.e. Langmuir probe and emission spectroscopy for atmospheric pressure glow discharge plasma in helium. For the measurement of plasma parameters, ramped probe I-V characteristics curves were used for probe diagnostics and line intensity ratios were used for spectroscopic diagnostics. An attempt has been made to crosscheck the measurements using different techniques for their validation. The variation of the plasma parameters i.e. electron density and temperature with external tunable parameters viz. applied voltage and frequency is also investigated to find the scaling of plasma parameters with external controls. Estimated electron density is ~1011 cm -3 and electron temperature is ~10 eV. Measured plasma parameters indicate suitability of the plasma which can be exploited for microwave invisibility.