Partial and total dielectronic recombination rate coefficients for W73+ to W56+

Abstract

Dielectronic recombination (DR) is a key atomic process that affects the spectroscopic diagnostic modeling of tungsten, most of whose ionization stages will be found somewhere in the ITER fusion reactor: in the edge, divertor, or core plasma. Accurate DR data are sparse while complete DR coverage is unsophisticated (e.g., average-atom or Burgess General Formula), as illustrated by the large uncertainties that currently exist in the tungsten ionization balance. To this end, we present a series of partial final-state-resolved and total DR rate coefficients for W73+ to W56+ tungsten ions. This is part of a wider effort within The Tungsten Project to calculate accurate dielectronic recombination rate coefficients for the tungsten isonuclear sequence for use in collisional-radiative modeling of finite-density tokamak plasmas. The recombination rate coefficients have been calculated with autostructure using κ-averaged relativistic wave unctions in level resolution (intermediate coupling) and configuration resolution (configuration average). Comparison with previous calculations of total DR rate coefficients for W63+ and W56+ yield agreement to within 20% and 10%, respectively, at peak temperature. It is also seen that the Jüttner correction to the Maxwell distribution has a significant effect on the ionization balance of tungsten at the highest charge states, changing both the peak abundance temperatures and the ionization fractions of several ions.