How thermal are (certain) thermal plasmas?

Abstract

Summary form only given, as follows. In a recent study Gao et al. (1999) have examined the assumption of a Maxwellian electron distribution function for an inductively coupled argon plasma at atmospheric pressure. By solving the Boltzmann equation the authors demonstrate that in fact deviations from a Maxwellian distribution can be detected. In this presentation we revisit the conclusions obtained by Gao et al. (1999). At atmospheric pressures and excitation frequencies of 3.0 MHz and 27.1 MHz it is not obvious that the electron distribution function (EDF) can be derived from the steady-state Boltzmann equation. For low degrees of ionization and at atmospheric pressure, the EDF would show a strong temporal modulation in the high energy part due to inelastic collisions. At high degrees of ionization, Coulomb collisions can dampen these oscillations and lead to a less modulated EDF tail. In this presentation, we discuss the EDF formation for the conditions presented. We present results from solutions of the electron Boltzmann equation and discuss possible deviations from non-Maxwellian distribution functions.