Nonlocal electrodynamics effects in ICPs

Abstract

Summary form only given. Most of the current models of inductively coupled plasma (ICP) use a local relation between RF current density and the electric field in the form of the Ohm's law. However, in the weakly collisional regime, when the effective mean free path of electrons is comparable or exceeds the characteristic scale of the RF electric field decay, the plasma conductivity is a nonlocal integral operator. In a simple case, this situation corresponds to the condition of anomalous skin effect. In the general case, the RF current distribution is determined by the geometry of the system, the nature of the electron trajectories, and the configuration of the external fields. In this talk we review the basics of anomalous skin effect and recent experiments with a flat coil ICP source carried out over a wide range of gas pressure and RF frequency. The electron energy distribution function (EEDF) and the space distribution of the RF electric field and current density measured in experiment have revealed several peculiarities in the electrodynamics of a weakly collisional ICP. A nonmonotonic distribution of the RF fields and current density, phase bifurcation, collisionless and negative power absorption and frequency dependence of the EEDF found in the experiments are interpreted in terms of nonlocal electrodynamics as result of electron thermal motion in the weakly collisional plasma.