High Temperature Plasma Radiation: A Study of the Recombination Continuum of Argon in the Ultraviolet and of the Conditions for Equilibrium in Nitrogen ARCS

The absolute intensity of the recombination continuum of argon was measured at wavelengths between 150 and 300 nm. The continuum radiation was produced in constricted arcs operating in argon at atmospheric pressure. The measurement of the absolute intensity of the continuum at wavelengths between 170 and 300 nm was facilitated through the use of a deuterium discharge lamp as a calibrated source of spectral radiance. Nitrogen arc measurements of the intensity of the 4915 A - 4935 A NI doublet and of the 3995 A NII line show that local thermodynamic equilibrium cannot be assumed in nitrogen arcs at electron densities below 1 x 10 to the 17th power/cc. Below this point, the results suggest that gas and electron temperatures differ significantly and that ground states are overpopulated with respect to upper electronically excited states. (Modified author abstract) Prepared in cooperation with Science Applications, Inc., McLean, Va.