Electron recombination with tungsten ions with open f-shells

TL;DR

This paper presents a statistical theory for electron recombination with tungsten ions having open f-shells, accounting for dense chaotic resonances, and provides temperature-dependent rates useful for plasma modeling in thermonuclear reactors.

Contribution

It introduces a novel statistical approach to model multi-electronic recombination via chaotic resonances, extending traditional dielectronic recombination theory for complex ions.

Findings

Recombination rates are enhanced by 2-3 orders of magnitude due to chaotic resonances.

Theoretical rates agree with experimental data for W$^{18+}$, W$^{19+}$, and W$^{20+}$.

Predictions for higher charge states are provided for plasma applications.

Abstract

We calculate the electron recombination rates with target ions W$^{q+}$, $q = 18$ -- $25$, as functions of electron energy and electron temperature (i.e. the rates integrated over the Maxwellian velocity distribution). Comparison with available experimental data for W$^{18+}$, W$^{19+}$, and W$^{20+}$ is used as a test of our calculations. Our predictions for W$^{21+}$, W$^{22+}$, W$^{23+}$, W$^{24+}$, and W$^{25+}$ (where the experimental data are not available) may be used for plasma modelling in thermonuclear reactors. The results for the temperature dependent rates for each ion are fitted with the standard analytical expressions to make them easy to use. All of these ions have an open electron $f$-shell and have an extremely dense spectrum of chaotic many-electron compound resonances which enhance the recombination rates by 2-3 orders of magnitude in comparison with the direct electron recombination. Conventional dielectronic recombination theory is not directly applicable in this case. Instead, we developed a statistical theory based on the properties of chaotic eigenstates. This theory describes a multi-electronic recombination (extension of the dielectronic recombination) via many-excited-electron compound resonances.