Nonequilibrium Hydrogen/nitrogen Plasmas Studies Using a Cascade Arc

A cascade arc facility has been constructed at The University of Tennessee Space Institute (UTSI) to study the effect of nonequilibrium transport properties in hydrogen-nitrogen arcjet propellant plasmas. These studies are being used to guide development of the physical models required for further development of arcjet computational codes. The cascade arc has been operated on hydrogen with a current of 50 A at pressures of 2.0 psi and 6.0 psi. Spatially resolved spectral data at these conditions have been collected for the Balmer H,, HP, I+, and Hz lines. The experimental H, lineshapes have been fitted to theoretical, Stark broadened, H, lineshapes to determine the radial distributions of electron number density. Radial profiles of an equilibrium plasma temperature have also been estimated from Boltzmann plots using the line emission from H,, HP, 5, and Hg lines. The electron number densities and plasma temperatures were compared to values predicted by nonequilibrium and equilibrium cascade arc simulations using the UTSI Cascade Arc Plasma Simulation (CAPS) code. The nonequilibrium computer simulations were run using three different sets of finite rate chemical kinetics. By varying finite rate chemical kinetics in the nonequilibrium simulation code, the experimental electric field has been predicted. The nonequilibrium simulations underpredict the peak experimental number densities between 30 percent and 1.5 orders of magnitude. The peak plasma temperature is overpredicted by the simulations by as much as a factor of two. In general, however, the radial profiles of the nonequilibrium solutions better match the experimental measurements.