Discrepancy between modelled and measured radial electric fields in the scrape-off layer of divertor tokamaks; A Challenge for 2D fluid codes?

Chankin, A. V.*; Coster, D. P.*; Asakura, Nobuyuki; Bonnin, X.*; Conway, G. D.*; Corrigan, G.*; Erents, S. K.*; Fundamenski, W.*; Horacek, J.*; Kallenbach, A.*; et al.

Nuclear Fusion, 47(5), p.479 - 489, 2007/05

https://doi.org/10.1088/0029-5515/47/5/013

Radial electric field in known to be one of the drivers for the parallel ion flow in the SOL. It contributes to the ion Pfirsch-Schluter flow and determines the return parallel flow compensating poloidal ExB drift. It was established recently that 2D fluid codes EDGE2D and SOLPS underestimate the predicted Er in the SOL compared to experimentally measured values. The present work demonstrates that this underestimate can be responsible for the large discrepancy between measured and simulated parallel ion flows in the SOL. Provided radial electric field was modelled correctly by the codes, an increase in the predicted Mach number of the parallel ion flow by up to a factor 3 for the JET could be expected. This would entirely eliminate the difference between the experimentally determined part of the ion flow that depends on the toroidal field direction, and the modelled ion flow attributed to drifts. Discrepancy between measured and simulated flows in ASDEX-Upgrade was also reduced.