Relationship between the induction frequency and LTE in inductively coupled plasmas

Abstract

Summary form only given. The effect of the induction frequency on the local thermodynamic equilibrium (LTE) conditions in an inductively coupled plasma (ICP) was investigated. Results were obtained for an atmospheric argon plasma under different operating conditions. Computations were carried out for an 18-mm-diameter ICP torch operating at 1 kW and argon flow rates of up to 16.2 slpm. The induction frequency varied from 3 to 40 MHz. Results were obtained by two different models. The first was based on LTE while the second one was the two-temperature model. Both models predict that the temperature levels in the torch decrease as a result of increase in frequency. The two-temperature model predicts higher electron temperatures than the heavy atom/ion temperature; this difference increases with frequency. Another important result is that the LTE predictions are consistently higher than those of the two-temperature model. This is an important difference, considering that it is the atom/ion temperature that is responsible for the heating and evaporating of aerosols or powders. Thus, for the conditions considered, the LTE predictions will overestimate the particle heating substantially