Investigation of equilibrium in an argon plasma

Abstract

Spectroscopic measurements of the 7635.10 ArI line were made on an argon plasma generated in a free burning arc at 0.1 atm, 0.5 atm, and 1.0 atm. By making absolute line intensity measurements and assuming LTE, the transition probabilities at these three pressures were obtained. They varied from 1.37 × 10 7 sec -1 at 0.1 atm to 2.3 × 10 7 sec -1 at 1.0 atm indicating the plasma was not in LTE. Extrapolating the data to higher pressures indicates that LTE occurs at about 3 atm (electron number density ∼ 10 18). The transition probability for this line is determined to be 2.7 × 10 7 sec -1. The plasma is believed to be in “Partial LTE” and the overpopulation of the ground state level of the atoms agrees with the theoretical results for a hydrogen plasma.