Lorentz force effects on the electron energy distribution in inductively coupled plasmas

Depletion of the electron energy distribution function by slow electrons in the skin layer has been observed in experiment in a cylindrical inductive discharge with a flat coil at low frequency and low gas pressure. The origin of the effect lies in the dependence of the ponderomotive force (caused by the rf magnetic field) on the electron thermal motion under conditions of the anomalous skin effect. Analysis of the electron energy distribution based on the existence of adiabatic invariants for collisionless electron motion at low frequencies reveals enhanced anisotropy and time dependence of the electron distribution function due to strong rf magnetic fields and a polarization electrostatic potential at twice the driving frequency. The electron energy distributions calculated in the skin layer using experimentally measured electromagnetic fields and rf and dc potential profiles are in reasonable agreement with the experimental electron distributions.