Characteristic Kα emission of electron cyclotron resonance ion source plasmas

Abstract

This thesis presents the results of an investigation of the volumetric Kα emission rate/inner shell ionization rate from an Electron Cyclotron Resonance Ion Source (ECRIS) plasma tuned predominantly for high charge state ion production. The experimental work include four complimentary studies covering the influence of a parametric sweep of the four source tune parameters i.e microwave power, neutral gas flow, biased disc voltage and magnetic field on the volumetric Kα emission rate, an investigation into the gas mixing effect, an investigation into the effectiveness of double-frequency heating mode and finally an investigation into microwave induced electron losses (relative and direct) from the ECRIS plasma.

The parametric sweeps revealed that only the microwave power and neutral gas flow has a significant impact on the volumetric Kα emission rate. From the study it was concluded that this observation is presumably dictated by the plasma energy content. It is also argued that this novel plasma parameter i.e. the volumetric inner shell ionization rate can be used to benchmark numerical simulations on ECRIS plasmas as this plasma parameter can easily be reproduced by most simulation codes. The investigation into the gas mixing concluded that the ion cooling effect is in all likelihood the mechanism responsible for the favourable influence of the gas mixing. One of the mechanism responsible for the favourable influence of double-frequency heating was found to be due to the increasing electron density, based on the results of the various diagnostic probes. The latter two investigations were combined with optical emission spectroscopy to directly probe the ion density of different charge states. Finally, the electron losses from an ECRIS plasma were shown to correlate with the microwave power in both CW and pulsed operations. This investigation combined a number of diagnostic methods to develop the current understanding of this scarcely studied plasma process which predominantly affects the heated electron populations of the plasma.