Inner shell ionization of argon in ECRIS plasma

Abstract

The volumetric Kα emission rate of argon emitted from the electron cyclotron resonance (ECR) heated plasmas of the JYFL (University of Jyväskylä, Department of Physics) 14 GHz ECR ion source (ECRIS) and the 14.5 GHz Grenoble Test Source (GTS) at iThemba Laboratory for Accelerator Based Sciences have been measured to gain an understanding of the influence of the ion source tune parameters on the absolute inner shell ionization rate. It was observed that the behaviour of the ionization rate and the extracted ion beam currents react differently, depending the parametric sweep performed. The neutral gas pressure and incident microwave power was found to have the strongest influence on the ionization rate. At high neutral gas pressure, the absolute inner shell ionization rate was found to saturate. This observation is as a result of the plasma energy content becoming insufficient to sustain the growth in ionization rate. It was also observed that the incident microwave power should be increased much more to counter the decrease in high charge state production as a result of the gas increase and subsequent increase in charge exchange. At low incident microwave, the ionization rate per unit absorbed microwave power was found to be high, which suggests that the inner shell ionization process is driven by the ion dynamics as opposed to the electron dynamics. The influence of the biased disc voltage and magnetic field configuration on the ionization rate was found to be minimal. This led to the suggestion that these two tune parameters does not directly impact the warm electron population of the ECRIS plasma during the parametric sweeps. The Kα emission rate can be used as an additional tool for benchmarking the results of numerical simulation codes on ECRIS plasmas.