Low-Pressure Plasma Spectroscopic Diagnostics

Diagnostic techniques have recently been developed that permit the determination of the deviation from local thermal equilibrium (LTE) in subatmospheric electric arcs and plasma jets. A review is presented of the methods that are applicable to MPD (magnetoplasmadynamic) and arcjet thruster plasmas but that have not been used in space propulsion research. Appropriate plasma diagnostics can lead to increased thrust, better nozzle design, and improved modeling capabilities. These methods include nonintrusive techniques, and can determine the electron, T-e, gas, T-g, and total excitation, T-exa, temperatures, as well as the electron and atom densities, without using LTE or partial LTE assumptions. General relations for analysis and experimental results for argon constricted arcs, an art in a rotating magnetic field, and plasma torch jets are presented. The methods discussed can also be applied to plasma mixtures.