Measurement of nonequilibrium effects in thermal plasmas

Abstract- Spectroscopic measurements have been made in a 50kW RF induction plasma with argon at atmospheric pressure to assess both the importance of departures from local thermodynamic equilibrium in so-called thermal plasmas of interest to plasma processing and the significance of nonequilibrium in interpreting plasma diagnostics. In these experiments relative and absolute line intensities, continuum intensities, as well as the total radiation source strength, were separately obtained and interpreted in terms of a partial-equilibrium model. In this model the free and excited bound electrons are found to be mutually in equilibrium irrespective of departures from equilibrium with the ground state. The implications of these observations for plasma diagnostics are discussed