Recombination of W18+ ions with electrons: Absolute rate coefficients from a storage-ring experiment and from theoretical calculations

TL;DR

This study provides new experimental and theoretical data on the electron-ion recombination rates of W$^{18+}$ ions, revealing significantly higher rates at plasma-relevant temperatures than previously recommended, aiding fusion plasma modeling.

Contribution

It offers the first combined experimental and theoretical analysis of W$^{18+}$ recombination rates, improving accuracy for plasma modeling of complex ions.

Findings

Experimental recombination rates are 5-10 times higher than existing recommendations.

Theoretical calculations agree reasonably well with experimental data.

Results enhance atomic data accuracy for fusion plasma simulations.

Abstract

We present new experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W$^{18+}$([Kr] $4d^{10}$ $4f^{10}$) forming W$^{17+}$. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping, recombination resonances. In the temperature range where the fractional abundance of W$^{18+}$ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-$4f$-system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of new Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.