Speaker
Michael Faitsch
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.116.pdf
Effect of magnetic perturbations for ELM control on divertor heat loads
and detachment in ASDEX Upgrade
M.Faitsch, D.Brida, B.Sieglin, W.Suttrop, T.Lunt, T.Eich, M.Wischmeier, A.Herrmann,
the ASDEX Upgrade Team1 and the Eurofusion MST1 Team2
Max-Planck-Institute for Plasma Physics, Boltzmannstr. 2, D-85748 Garching, Germany
1 See appendix of "A. Kallenbach 2017 Nucl. Fusion 57 102015"
2 See author list of "H. Meyer et al 2017 Nucl. Fusion 57 102014"
The reduction of transient heat loads induced by edge localised modes (ELM) in H-Mode is
fundamental to the success of ITER/DEMO. The application of 3D magnetic perturbation (MP)
fields is studied as a method for ELM control and full ELM suppression in ASDEX Upgrade.
These 3D fields lead to toroidal asymmetries of the heat load pattern in the divertor that cause
further challenges for future devices. ASDEX Upgrade is equipped with a versatile set of MP
coils and high resolution edge and target diagnostics to characterise the impact of MPs on diver-
tor heat loads and the access to detachment. The heat flux in L- and H-Mode can be studied in
ASDEX Upgrade, thanks to the flexible power supply, with slowly rotating MP fields, allowing
the complete toroidal characterisation of the heat flux pattern.
For a scan of various poloidal perturbation field spectra in low density discharges, a large
toroidal variation is only observed in the so called resonant configuration which is foreseen
for ITER for ELM control. When the profiles are toroidally averaged and the standard 1D Fit-
Function for diffusive power spreading is applied, the same power fall-off length λq and divertor
broadening S as in the non-perturbed reference case is found throughout the scan.
With increasing density, while still being in attached conditions, the toroidal variation of the heat
flux pattern is reduced. This is accredited to an increase of S. The toroidal peaking, the toroidal
maximum divided by the mean value, decreases from 1.9 to 1.2 when increasing line averaged
edge density from 0.8 to 1.8 ·1019 m−3 in L-Mode. Here, S increases from 0.3 to 1.2 mm and
λq from 3.6 to 6.0 mm leading to an increase of the integral width λint - and thereby also a
reduction of normalised peak heat flux - by a factor of two.
By increasing the density even further, the toroidal peaking in the ITER relevant high recycling
regime reaches about unity. On the other hand, no detriment effect on the access to detach-
ment is observed. Hence, for ITER a problematic toroidal peaking of the inter-ELM heat flux
is expected to be alleviated by operating with high scrape-off layer and/or divertor density and
thereby a cold divertor. However, ELM filaments lock to the perturbation and may lead to en-
hanced sputtering at distinct toroidal locations if no variation of the perturbation is applied.
