Optical Diagnostics for Plasma Arcs

Abstract

Artificially generated atmospheric pressure plasma arcs, with core temperatures on the order of 1 eV, are representative of conditions expected to occur within magnetohydrodynamic (MHD) generators, where arcs between the plasma and electrodes place stringent limitations on the lifetime of such systems. As such, a detailed analysis of these arcs is necessary for the construction of more sophisticated MHD converters. We describe the theory and implementation concerns of a near-resonance optical schlieren (NROS) diagnostic and a Fourier-transform infrared spectroscopy (FTIR) diagnostic for analyzing atmospheric plasma arcs. The FTIR and NROS diagnostics provide complementary information about arc composition and temperatures. They are additionally accompanied by predictive modeling performed using NASA’s Chemical Equilibrium with Applications (CEA) program. Using the arc model and theoretical foundations of NROS, we develop a method for determining the ideal frequency to use in future NROS applications.