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 ionization stages, are essential to model tungsten. We describe a set calculations performed using the distorted wave code autostructure for the tungsten ions W 37+ to W 28+ . 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 ionization fraction for tungsten. We find that, relative to the ionization fraction calculated using the recombination rate coefficients of Putterich et al (Plasma Phys. Control. Fusion, 50, 085016), the peak temperatures of W 37+ to W 28+ ionization states are shifted to lower temperatures spanning 0.9-1.6keV. 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.

Maxwellian rate coefficients for electron-impact ionization of W 26+

“…Our previous study reported the electron-impact MRC only from the ground levels of the ions [24][25][26]. The current results are presented for thirteen temperature values in the range from 1.46•10 6 K to 7.29•10 9 K. It should be noted that peak abundance temperature obtained from the modeling for W 26+ equals 1×10 7 K [27,28]. The study of MRC includes the EA channels corresponding to the excitations to shells with principal quantum numbers n 8 and 9 n 25.…”

Dielectronic recombination of lanthanide and low ionization state tungsten ions: W13+–W1+

“…Next, we show our results, and compare our rate coefficients to currently available literature. We then calculate an updated steady state ionization fraction including the data calculated in this work, and the data calculated in [11][12][13]. Finally, we conclude the paper, and discuss future work on the open 4f-shell of tungsten.…”

“…We now compare two sets of ionization fractions, calculated using recombination rate coefficient data from this work (61-to 73-like) and The Tungsten Project (00-to 46-like, [11,12,13]), and using the scaled data from Pütterich et al [3]. For the ionization fraction calculated using the present data, we use the data from Pütterich et al for 47-to 60-like, as we have not calculated data for these charge states yet.…”

“…In an attempt to resolve the disagreement, The Tungsten Project was created to calculate a set of final-state resolution DR and RR rate coefficients for tungsten using the distorted wave code AUTOSTRUCTURE [8][9][10]. To date, the project has produced DR and RR rate coefficients for W 74+ -W 28+ [11][12][13]. All data from The Tungsten Project is currently hosted on the Atomic Data Analysis Structure (ADAS) website 5 in the standard adf09 (DR) and adf48 (RR) formats, the specifications for which can also be found on the ADAS website.…”

Atomic structure and collision dynamics with highly charged ions

“…[124] In addition, a systematic theoretical calculations of recombination rate coefficients for tungsten ions have been performed by employing the AU-TOSTRUCTURE code and can be found in the references in Refs. [125][126][127].…”