Electron kinetics and non-Joule heating in near-collisionless inductively coupled plasmas

Abstract

Electron kinetics in an inductively coupled plasma sustained by a coaxial solenoidal coil is studied for the near-collisionless regime when the electron mean free path is large compared to the tube radius. Emphasis is placed on the influence of the oscillatory magnetic field induced by the coil current and the finite dimension of the plasma on electron heating and formation of the electron distribution function (EDF). A nonlocal approach to the solution of the Boltzmann equation is developed for the near-collisionless regime when the traditional two-term Legendre expansion for the EDF is not applicable. Dynamic Monte Carlo (DMC) simulations are performed to calculate the EDF and electron heating rate in argon in the pressure range 0.3--10 mTorr and driving frequency range 2--40 MHz, for given distributions of electromagnetic fields. The wall potential ${\mathrm{\ensuremath{\varphi}}}_{\mathrm{w}}$ in DMC simulations is found self-consistently with the EDF. Simulation results indicate that the EDF of trapped electrons with total energy \ensuremath{\varepsilon}${\mathrm{\ensuremath{\varphi}}}_{\mathrm{w}}$ is almost isotropic and is a function solely of \ensuremath{\varepsilon}, while the EDF of untrapped electrons with \ensuremath{\varepsilon}ge${\mathrm{\ensuremath{\varphi}}}_{\mathrm{w}}$ is notably anisotropic and depends on the radial position. These results are in agreement with theoretical analysis.