TEMPERATURE AND DENSITY-MEASUREMENTS IN A RECOMBINING ARGON PLASMA WITH DILUENT

Spectroscopic and calorimetric measurements of temperature and number density have been made using a 50-kW radio-frequency inductively coupl ed plasma (RFICP) torch operated at atmospheric pressure with maximum temperatures and electron densities near 8,100 K and 2 x 10(21) m-3, r espectively. These measurements enabled the determination of the state of equilibrium and of the corresponding applicability of various diag nostic techniques in both a recombining argon plasma and a recombining plasma with hydrogen or nitrogen. Results indicate that the pure argo n plasma is well described by a partial equilibrium model in which the free and bound-excited electrons are in mutual equilibrium irrespecti ve of possible departures from equilibrium with the ground state. The addition of just tenths of a percent of either atomic hydrogen or nitr ogen, however, disturbs this partial equilibrium in argon plasmas with electron densities roughly less than 10(21) m-3 such that only diagno stic techniques which are independent of partial equilibrium assumptio ns can be reliably implemented