Speaker
Description
See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1031.pdf
he tungsten ion average charge states in EDGE2D-EIRENE simulations of the JET scrape-off layer are predicted to decrease by up to 40% when the 74 ion states are bundled into 6 fluid stages, compared to reference cases using the Monte Carlo code DIVIMP and a more elaborate bundling scheme in EDGE2D-EIRENE. The ionization state has a major impact on the W force balance in the SOL and thereby also on the accumulation of W in the core plasma.
W radiation cools down the core plasma such that W concentration much above 10^-5 causes intolerable loss of performance in a fusion reactor [1]. Comparison of W transport code predictions in computationally more accessible L-mode plasmas allows the identification of potential ways to improve prediction accuracy of the core W content using edge fluid codes. The studied simulations are L-mode plasmas [2] with deuterium as the main species
and beryllium and tungsten as intrinsic impurities. The main source of tungsten in the EDGE2D-EIRENE cases is sputtering due to beryllium ions at the HFS divertor and charge-exchange deuterium neutrals at the LFS divertor [3]. The simulations are validated against experiment using divertor spectroscopy of neutral and singly ionized tungsten emission lines.
EDGE2D-EIRENE simulations with tungsten ion stages for charges 1, 2-6, 7-12, 13-22, 23-73 and 74 predict the same tungsten charge profile as DIVIMP in the core region, but
the average charge states in the SOL tend to be approximately 30% lower in EDGE2D-EIRENE than in DIVIMP. This results in the core W concentration in DIVIMP exceeding EDGE2D-EIRENE predictions by around 50%. When the bundling scheme in EDGE2D-EIRENE is changed to include each individual charge up to 20+, all charge states residing in the SOL, the predicted charge states match those predicted with DIVIMP in all regions. Earlier assessments of the impurity bundling scheme in EDGE2D-EIRENE found only a weaker bundling effect of order 10% on W core leakage when injecting tungsten at the LFS mid-plane [4]. The usage of large amounts of ionization stages greatly increases computation time and lowers code stability. Therefore, the Monte Carlo approach or bundling schemes
prioritizing charge states 1-15 may be considered.
[1] T. Pütterich et al., Nucl. Fusion 50(2010)025012 [3] D. Harting et al., J. Nucl. Mater. 438(2013)S480-S483 [2] M. Groth et al., Nucl. Fusion 53(2013)093016 [4] J.D. Strachan et al., J. Nucl. Mater. 415(2011)S501-S504
