Non-equilibrium behavior of low-pressure plasma jets

Summary Form only given, as follows. The establishment of local thermodynamic equilibrium (LTE) in optically thin plasmas requires that collision processes dominate, which implies that large electron densities exist in the plasma. The electron density in low-pressure plasma jets will be marginal for establishing one of the requirements for LTE, namely, ionization equilibrium. Because of this small electron density and high velocities typically encountered in the low-pressure plasma deposition process (LPPD), substantial deviations from ionization equilibrium are expected. Deviations from kinetic equilibrium are also anticipated, because the excess energy that electrons acquire in the recombination processes (three-body recombination) cannot be readily transferred to the heavy species due to the poor collisional coupling between the electrons and the heavy particles. Therefore, it is anticipated that the electron temperature will be higher than the heavy particle temperature. A two-temperature description of plasma jets in chemical nonequilibrium has been developed, using finite rate chemistry for ionization and recombination processes. The results clearly indicate the validity of LTE at atmospheric pressure as well as strong deviations from LTE at lower pressures, especially in terms of chemical equilibrium.<>