Analysis of the charge state distribution in Ar plasma (Vol. 44 No. 5)

Double crystal X-ray spectrum showing Ar12+ to Ar14+ transitions.

Investigation of charge state distributions (CSD) in astrophysical as well as laboratory plasmas, such as those provided by electron-beam ion traps, electron– cyclotron-resonance ion source (ECRIS) and tokamaks, is very important for the understanding of plasma processes. This knowledge is crucial for the optimization of a given ion source so that higher yields of higher charge states can be obtained. Furthermore, characterization of the CSD enables precise diagnostics of injected elements and impurities, which are important for the performance of fusion devices.

In this work, we have determined the CSD of an Ar plasma through the analysis of x-ray spectra obtained with a double crystal spectrometer. It is the first time that such a spectrometer is used coupled to an ECRIS for measuring inner-shell transitions in highly charged ions. The very high resolution of this apparatus enables us to correctly obtain the CSD of the plasma from x-ray spectra, even in highly populated energy regions.

Comparison to extracted ion currents show that the CSD in the center of the plasma can be quite different from the ion beam yields, due to the fact that the ions are extracted from the plasma edges.

M. Guerra, P. Amaro, C.I. Szabo, A. Gumberidze, P. Indelicato and J.P. Santos, 'Analysis of the charge state distribution in an ECRIS Ar plasma using high-resolution x-ray spectra', J. Phys. B: At. Mol. Opt. Phys. 46, 065701 (2013)