X-ray-spectroscopy analysis of electron-cyclotron-resonance ion-source plasmas

Analysis of x-ray spectra emitted by highly charged ions in an electron-cyclotron-resonance ion source (ECRIS) may be used as a tool to estimate the charge-state distribution (CSD) in the source plasma. For that purpose, knowledge of the electron energy distribution in the plasma, as well as the most important processes leading to the creation and de-excitation of ionic excited states are needed. In this work we present a method to estimate the ion CSD in an ECRIS through the analysis of the x-ray spectra emitted by the plasma. The method is applied to the analysis of a sulfur ECRIS plasma.

Figure 1

$K$-shell ionization cross section of Ar. Solid circles, experimental data by Tawara et al. [85]; squares, experimental data by Hippler et al. [86]; solid upright triangles, experimental data by Quarles and Semaan [87]; upright triangles, experimental data by Platten et al. [88]; thick solid curve, present RBEBav cross section Eq. (5); dot-dashed curve, nonrelativistic empirical formula by Lotz [44, 89]; dashed curve, nonrelativistic empirical formula by Casnati et al. [46]; dotted curve, the Casnati cross section with relativistic corrections by Quarles [47]; dot-dot-dashed curve, relativistic semiempirical formula by Deutsch et al. [45].

Figure 2

$K$-shell ionization cross section of Ar. Solid circles, experimental data by Scholz et al. [90]; squares, experimental data by Berenyi et al. [53]; solid upright triangles, experimental data by Kiss et al. [91]; thick solid curve, present RBEBav cross section Eq. (5); dot-dashed curve, nonrelativistic empirical formula by Lotz [44, 89]; dashed curve, nonrelativistic empirical formula by Casnati et al. [46]; dotted curve, the Casnati cross section with relativistic corrections by Quarles [47]; dot-dot-dashed curve, relativistic semiempirical formula by Deutsch et al. [45].

Figure 3

Excitation, ionization, and decay processes considered in this model: $K$ excitation, dashed line; single $K$ ionization, dot-dashed line; double $\mathit{KL}$ ionization, dot-dot-dashed line; triple KLL ionization, dot-dot-dot-dash-dashed line; radiative decay, solid line, and radiationless decay, dotted line.

Figure 4

Theoretical spectra of a sulfur plasma (solid curve) plotted against experimental data (dots) in log scale (a) and linear scale (b). Peak 1 refers to the M1 1$s$ 2$s$ ${}^3$$S$${}_1$ $\to$ 1$s$${}^2$ line, and peak 2 to the 1$s$ 2$s$ 2$p$ ${}^2$$P$${}_{1/2,3/2}$ $\to$ 1$s$2 2$s$ lines and to the 1$s$ 2$p$ ${}^3$$P$${}_1$ $\to$ 1$s$${}^2$ line. The experimental data were obtained in the PSI ECRIT [11].