Multiply-charged ion emission from a cyclotron-resonance-heated plasma ion source.

Abstract

Electron cyclotron resonance heated ion sources have become the prominent electron-stripping device used to produce multiply-charged ions. These ions are required for many applications ranging from atomic physics research to cyclotron injection. Unfortunately, many of these sources are designed, built and operated based on empirical knowledge acquired from past or existing machines. Much research remains to be performed before a solid underst and ing of the physical processes governing these sources can be gained. The work presented here attempts to partially bridge the gap between application and underst and ing. A time-of-flight spectrometer diagnostic system was implemented on MIMI to measure the endloss current density for specific charge states flowing from the mirror. The method of acquiring many spectra in a given shot over a relatively short span of real time, and averaging them to produce one averaged spectrum has proven quite effective in reducing r and om signal fluctuations. Also, shot-to-shot reproducibility becomes possible with this method--a difficult and most welcome result. Ion cyclotron heating has been shown to increase ion temperatures tens of eV. The resonant species typically experiences the greatest temperature increase but transfers much of its energy to the remainder of the distribution via collisions. These temperature increases are consistent with those expected from antenna loading computations. Modeling of the important physical processes occurring in the plasma yields results consistent with those measured with the time-of-flight spectrometer. The endloss charge state distributions generally possess an overall low average Z. Measurements show ion cyclotron heating has a detrimental effect on the endloss charge state distributions--decreasing the confinement of high-Z ions and causing a shift to low charge states to maintain charge neutrality. These same ICRH effects are predicted by the system modeling. The model is then used to determine the confined steady-state densities and ICRH effects on the confined charge state distributions. These distributions exhibit the same general trends as the endloss, modified somewhat by the changing confinement with ICRH. Steady-state charge state distributions and ICRH effects have been investigated for oxygen, neon, and argon.