Ponderomotive effects in an electromagnetic accelerator

Abstract

An inductive coupled plasma (ICP) source of a new type for dry etching has been developed. It is driven by a planar inductive coil, which is placed at the top of the channel formed by two coaxial dielectric cylinders. At low pressure, the radial component of the radiofrequency (RF) magnetic field causes a ponderomotive force acting on the electrons directed towards the bottom of the channel. Charge separation gives rise to an ambipolar electric field, which retards electrons and accelerates ions. The source represents an electrodeless electromagnetic accelerator (EMA) and can create an axially directed flux of ions. EMA has been modeled as an axisymmetric ICP discharge in argon gas based on experimental data of the plasma density and electron temperature profile. The magnetic field and RF current densities obtained have been used for calculation of the Lorentz force acting on the electrons and ambipolar plasma potential. Simulations of electron trajectories show that electrons are trapped in the EMA channel and make a number of oscillations before leaving the channel. The ponderomotive potential produces acceleration of the ions in the channel up to 13–16 eV.