Plasma and electrical characteristics of inductive discharge in a magnetic field

Abstract

The electron energy distribution function and the azimuthal rf electric field (magnitude and phase) have been measured in a cylindrical inductively coupled plasma (ICP) immersed in a weak magnetic field and driven at 29 MHz. The measurements were performed under conditions of controlled rf power delivered to the plasma electrons taking into account power loss in the induction coil. It has been found that considerable modification of plasma parameters at electron cyclotron resonance (ECR) conditions occurs only at relatively small discharge power and plasma density, when electron–electron collisions are negligible. It is shown that enhancement in the plasma density with application of magnetic field found in earlier experiments is mainly due to a rise in the power transfer efficiency caused by reduction in the ICP sustaining rf electric field. The rf field reduction is due to strong cyclotron damping at ECR conditions and due to the onset of propagation and absorption of the wave for which the phase velocities were found to be close to the electron thermal velocity. This wave regime occurs at magnetic fields higher than that at ECR but much smaller than that in typical helicon plasma sources.