# Recombination of open-f-shell tungsten ions

## TL;DR

This paper reviews experimental and theoretical studies on electron recombination with highly-charged tungsten ions with open 4f shells, crucial for plasma modeling in fusion reactors, and introduces a new computational approach for accurate rate coefficients.

## Contribution

It presents a novel ab-initio computational method that reliably predicts plasma recombination rates for open 4f-shell tungsten ions, improving upon previous models.

## Key findings

- Storage-ring experiments provided high-resolution recombination data.
- Significant deviations from simplified models were observed.
- New ab-initio calculations offer more accurate plasma rate coefficients.

## Abstract

We review experimental and theoretical efforts aimed at a detailed understanding of the recombination of electrons with highly-charged tungsten ions characterised by an open 4f sub-shell. Highly-charged tungsten occurs as a plasma contaminant in ITER-like tokamak experiments, where it acts as an unwanted cooling agent. Modelling of the charge state populations in a plasma requires reliable thermal rate coefficients for charge-changing electron collisions. The electron recombination of medium-charged tungsten species with open 4f sub-shells is especially challenging to compute reliably. Storage-ring experiments have been conducted that yielded recombination rate coefficients at high energy resolution and well-understood systematics. Significant deviations compared to simplified, but prevalent, computational models have been found. A new class of ab-initio numerical calculations has been developed that provides reliable predictions of the total plasma recombination rate coefficients for these ions.