How thermal are (certain) thermal plasmas?

In a recent study Gao et al. 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 in [1]. 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 in [1]. We present results from solutions of the electron Boltzmann equation and discuss possible deviations from non-Maxwellian distribution functions.