Dielectronic recombination of the open 4d-shell of tungsten: W37+–W28+

Abstract

Tungsten is an important element for magnetically confined fusion plasmas but has the potential to cool, or even quench the plasma due to it being an efficient radiator. Total and level-resolved dielectronic recombination (DR) rate coefficients, for all ionisation stages, are essential to model tungsten. We describe a set calculations performed using the distorted wave code autostructure for the tungsten ions –. We demonstrate the importance of relativistic configuration mixing in such calculations. In particular, we show that the partial DR rate coefficients calculated in level and configuration resolution can differ by as little as 5%, and up to as much as 75%. Using the new data, we calculate a revised steady-state ionisation fraction for tungsten. We find that, relative to the ionisation fraction calculated using the recombination rate coefficients of Putterich et al (2008 Plasma Phys. Control. Fusion 50 085016), the peak temperatures of – ionisation states are shifted to lower temperatures spanning 0.9–1.6 keV. This temperature range is important for understanding the performance of large tokamaks, such as ITER, because the temperatures in the pedestal, edge, scrape-off-layer and divertor region fall in this range.