Dissipation of microwaves propagating through atmospheric pressure glow discharge plasma

Summary form only given. The atmospheric pressure glow discharge (APGD) is a cold collisional, non-equilibrium plasma that explores wide applicability of plasma for modifying aerodynamic properties specially the drag reduction and also for radar cross-section (RCS) reduction by microwave invisibility. The experimental study has been carried out to develop some information for microwave dissipation in the plasma to cease the radar function. The cold plasma produced at atmospheric pressure can absorb the microwave power because of its complex dielectric constant and diffuse density profile. The attenuation of microwaves in the plasma depends on the discharge operating parameters to create sufficient plasma density and thickness, incident wave frequency and electron-neutral collision frequency for momentum transfer etc. The uniform glow discharge was ignited between parallel-plate dielectric covered electrodes as well as on a planar surface in helium gas at atmospheric pressure. The first experiment was performed with the measurements in parallel-plate electrode geometry. The electron plasma density has been measured using optical emission spectroscopy with helium line intensity ratio method that was verified by electron density obtained by microwave attenuation measurements. Hence, the measurement of microwave attenuation was also used as a diagnostic method to estimate the electron plasma density. The microwave signal was launched to the plasma by a Gunn oscillator (X-band) and transmitted signal was detected by high sensitivity microwave detector. The attenuation in transmitted signal was measured for various operating parameters. The measured attenuation was in good agreement with the theoretical prediction for defined plasma parameters. Further experiments are in progress to measure the microwave attenuation in planar surface discharge at various plasma and wave parameters. The details of the experimental setup and results of these studies will be presented