Speaker
Samuel Aaron Lazerson
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1036.pdf
Analysis of Wendelstein 7-X divertor load symmetrization
S. A. Lazerson1 , S.A. Bozhenkov2 , M. Otte2 , Y. Gao3 , H. Niemann2 , A. Ali2 ,
P. Drewelow2 , M. Jakubowski2 , F. Pisano4 , A. Puig Sitjes2 , T. Andreeva2 , V. Bykov2 , M. Endler2 ,
and the W7-X Team2
1 Princeton Plasma Physics Laboratory, Princeton, USA
2 Max-Planck Institut für Plasmaphysik, Greifswald, Germany
3 Forschungszentrum Jülich, Jülich, Germany
4 University of Cagliari, Cagliari, Italy
The achievement of long pulses in the first divertor campaign (OP1.2a) on Wendelstein 7-X
(W7-X) required the development of trim coil scenarios which ensured heat load symmetry
among the ten divertor modules. Application of magnetic fields from these five copper coils
located outside the cryostat, allowed actuation of the n = 1 components of the error fields. A
series of compass scans were performed where the amplitude of the applied n = 1 field and
phase (relative to the device) were varied [1]. The corresponding change in divertor heat loads
were measured using thermocouples located in the carbon divertor tiles and through a set of
infrared camera measurements. These scans were used to develop a map of the divertor asym-
metry allowing prediction of trim coil currents which best symmetrize the divertor heat loads.
This method was employed to characterize the correcting field for many of the magnetic con-
figurations produced by the superconducting coil set. Correction was found to require around
10% the rated trim coil capacity, confirming previous limiter results that error fields were small
[2, 3, 4, 5]. Comparison with flux surface measurements suggests that error fields comprise the
majority of the symmetry breaking phenomena. From this we infer that the divertor structures
themselves are well aligned and that any misalignment is small and easily correctible by appli-
cation of trim coil currents. Assessments of the ten in-vessel control coils capability to correct
both n = 1 and n = 2 fields are presented.
References
[1] S.A. Lazerson et al., Plas. Phys. Cont. Fusion, (submitted) (2018)
[2] T.S. Pedersen et al., Nature Comm. 7 (2016)
[3] S.A. Lazerson et al., Nuclear Fusion 56, 10 (2016)
[4] S.A. Lazerson et al., Nuclear Fusion 57, 4 (2017)
[5] S.A. Bozhenkov et al., Nuclear Fusion 57, 12 (2017)
