Dielectronic recombination of W^20+ (4d^10 4f^8): addressing the half-open f-shell

TL;DR

This study investigates the dielectronic recombination of W^20+ ions, revealing significant near-threshold resonances that impact plasma modeling, and compares experimental data with advanced theoretical calculations to improve understanding of complex atomic processes.

Contribution

The paper provides detailed AUTOSTRUCTURE calculations including all significant promotions, and demonstrates how chaotic mixing assumptions can reconcile theory with experimental results.

Findings

Near-threshold resonances significantly affect recombination rates.

Intermediate coupling results are much larger than LS-coupling ones.

Chaotic mixing assumptions improve agreement with experimental data.

Abstract

A recent measurement of the dielectronic recombination (DR) of W^20+ [Schippers et al Phys. Rev. A83, 012711 (2011)] found an exceptionally large contribution from near threshold resonances (<1eV). This still affected the Maxwellian rate coefficient at much higher temperatures. The experimental result was found to be a factor 4 or more than that currently in use in the 100-300eV range which is of relevance for modeling magnetic fusion plasmas. We have carried-out DR calculations with AUTOSTRUCTURE which include all significant single electron promotions. Our intermediate coupling (IC) results are more than a factor of 4 larger than our LS-coupling ones at 1eV but still lie a factor 3 below experiment here. If we assume complete (chaotic) mixing of near-threshold autoionizing states then our results come into agreement (to within 20%) with experiment below about 2eV. Our total IC Maxwellian rate coefficients are 50-30% smaller than those based-on experiment over 100-300eV.