Speaker
Yu Gao
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.104.pdf
Effects of toroidal plasma currents on the strike-line movements on W7-X
Y. Gao1 , M. Jakubowski2 , J. Geiger2 , M. Endler2 , P. Drewelow2 , S. Bozhenkov2 , K. Hammond2 ,
K. Rahbarnia2 , A. Puig Sitjes2 , F. Pisano3 , H. Niemann2 , A. Ali2 , H. Thomsen2 , T. Andreeva2 ,
U. Neuner2 , J. Schilling2 , M. Rack1 , Y. Liang1 , and the W7-X Team
1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik,
Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
2 Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany
3 Department of Electrical and Electronic Engineering, University of Cagliari, Piazza d’Armi,
Cagliari 09123, Italy
Wendelstein 7-X (W7-X) stellarator has been optimized amongst other criteria for small boot-
strap current. However, even small plasma currents can change the rotational transform and
displace the magnetic island chains at the plasma edge, due to its low shear characteristic. Be-
sides possible changes to the plasma core confinement, the power loads to the plasma facing
components are affected, which is most important for divertor operation. Thus scenarios with a
small bootstrap current are crucial for W7-X [1].
The evolution of toroidal plasma currents has been measured by a set of Rogowski coils [2, 3],
during the first divertor operation phase on W7-X. In the case of freely evolving bootstrap
currents (without electron cyclotron current drive), strike lines on the divertor targets monitored
by means of infra-red cameras are observed to move in accordance with the measured toroidal
current. The net positive toroidal current shifts the strike lines on the vertical and horizontal
targets away from the pumping gap in the standard magnetic configuration.
Heat flux profiles have been calculated and compared with diffusive field line tracing mod-
elling [4] considering also the effective plasma current. As a preliminary result we see qualita-
tive consistency between experimental results and modelling suggesting a strike-line movement
of ∼ 3 cm along the target surface caused by a net toroidal current of ∼ 5 kA. This current is
developed in the order of 10 s. This movement of the strike line corresponds to approximately
one third of the strike-line width.
References
[1] J. Geiger et al. Plasma Physics and Controlled Fusion, 57 (1), 014004 (2015).
[2] M. Endler et al. Fusion Engineering and Design, 100, 468 (2015).
[3] K. Rahbarnia et al. Nuclear Fusion, submitted.
[4] S. Bozhenkov et al. Fusion Engineering and Design, 88 (11), 2997 (2013).
