Scaling of L-mode heat flux for ITER and COMPASS-U divertors, based on five tokamaks

Abstract

This contribution aims to improve existing scalings of the L-mode power decay length λ q o m p , especially for plasma configurations with strike points at the ITER-relevant location—closed vertical divertor targets. We propose 13 new λ q o m p scalings based on data from the tokamaks JET, EAST, MAST, Alcator C-mod and COMPASS, and validate them against the output of the 2D turbulence code HESEL. The analysis covers 500 divertor heat flux profiles (obtained by probes or IR cameras), measured in L-mode discharges with varying 12 global plasma parameters (all well predictable). We find that the two previously published scalings (Eich 2013 J. Nucl. Mat. 438 S72) and (Scarabosio 2013 J. Nucl. Mat. 438 S426), which were based on outer target data from AUG and JET, describe the JET, C-mod and COMPASS profiles well. This holds not only at the outer horizontal and vertical targets, but surprisingly also at the inner vertical targets. In contrast, EAST, HESEL and especially MAST data are poorly described by these two scalings. We therefore derive 13 new scalings, which account for 85–92 % of the measured λ q o m p variability across all five tokamaks. Although each of the scalings is based on a different parameter combination, their predictions for the ITER and COMPASS-Upgrade tokamaks are very similar. Just before the L-H transition in the ITER baseline scenario, the presented scalings predict values λ q o m p = 3.0 ± 0.5 mm. For the COMPASS-Upgrade tokamak, all the scalings predict λ q o m p = 2.1 ± 0.5 mm with a single exception of the scaling based on the stored plasma energy which predicts only 1.2 mm for both tokamaks. We encourage the reader to use as many of these scalings as possible, depending on available data. In attached plasma and using significant assumptions, our results imply steady-state surface-perpendicular heat flux around 10 MW/m2 for ITER, and 20 MW/m2 for COMPASS-Upgrade.

Theory-based scaling laws of near and far scrape-off layer widths in single-null L-mode discharges

“…By combining five hundred L-mode outer and inner divertor heat flux profiles obtained by probes or IR camera, thirteen credible scaling laws have been derived. A scaling law in good agreement with the experimental data (describing R 2 =92% of data variation) obtained by considering only outer divertor measurements is [15] λ q = 2800 a R 0 1.03…”

“…For this purpose, we consider the multi-machine database of Ref. [15] that contains a set of power fall-off lengths obtained from a nonlinear regression of measurements of divertor heat flux profiles in attached conditions with probes or IR cameras on different tokamaks. Both favorable and unfavorable ion-∇B drift directions are considered.…”

“…Significant experimental efforts have been put in the past few years to derive experimental scaling laws of the power fall-off length in the near SOL at the divertor plates in L-mode diverted plasmas (see, e.g., Refs. [11][12][13][14][15]). Recently, a nonlinear regression has been carried out on a set of power fall-off length measurements from a multi-machine database including the COMPASS, EAST, Alcator C-Mod, MAST, and JET tokamaks [15].…”

“…[11][12][13][14][15]). Recently, a nonlinear regression has been carried out on a set of power fall-off length measurements from a multi-machine database including the COMPASS, EAST, Alcator C-Mod, MAST, and JET tokamaks [15]. By combining five hundred L-mode outer and inner divertor heat flux profiles obtained by probes or IR camera, thirteen credible scaling laws have been derived.…”

The European master of science in nuclear fusion and engineering physics (FUSION-EP): 15 years of experience

“…Results from the the 2-weeks Joint experiment and analysis session at IPP Prague have sometimes been included in regular publications (see e.g. [8,9,10]), a proof that the students can produce a valuable research work at the end of three semesters at FUSION-EP.…”