Speaker
Birger Buttenschön
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1063.pdf
Intrinsic impurity composition in helium and hydrogen discharges in
Wendelstein 7-X
B. Buttenschön, D. Zhang, Th. Wegner, R. Burhenn, and the W7-X Team
Max Planck Institute for Plasma Physics, Greifswald, Germany
Intrinsic impurities in fusion devices serve as an indicator for thermally overloaded in-
vessel components, but also constitute an important energy loss channel entering the global
energy balance of the confned plasma.
In the Wendelstein 7-X stellarator (W7-X), the impurity composition is constantly
monitored by means of the High Efciency XUV Overview Spectrometer (HEXOS) system.
The intensity calibration of the instrument, available over large parts of the covered
wavelength range, allows, combined with transport codes such as STRAHL, to estimate the
concentration of selected impurities. The transport coefcients employed in the calculations
are obtained from the evaluation of laser blow-of eeperiments that have been performed in
various discharge scenarios.
The intrinsic impurity composition (with C and O being the main impurities) and their
concentrations are evaluated for W7-X discharges in helium and hydrogen, which showed a
signifcant diference in overall plasma performance. In addition, the daily and the long-
term impurity concentration evolution are evaluated particularly with regard to the planned
wall boronization in the upcoming operation phase.
