Effect of Electromagnetic Waves Propagating in the Periphery of Electron Cyclotron Resonance Plasma on the Uniformity

Stable vacuum regions in the periphery of an electron cyclotron resonance (ECR) plasma near a quartz window were found to possibly contribute to plasma uniformity as a kind of a waveguide for incident electromagnetic waves. Mode conversion of electromagnetic waves with long wavelength into the right circularly polarized wave was observed clearly at a certain radial position. In order to investigate the effects of electromagnetic waves propagating in the vacuum region on plasma production or uniformity, microwave propagation in a partially filled plasma chamber was examined numerically. The numerical results indicated that the electromagnetic waves with long wavelengths in the periphery of the plasma were converted into extraordinary or electrostatic waves outside the ECR region and that power absorption took place locally. Furthermore, it was found to be strongly dependent on the width and shape of the vacuum region and gas pressure. Physical considerations of these results revealed the reason why plasma uniformity is influenced by a magnetic field gradient.