Speaker
Thierry Kremeyer
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1024.pdf
Light impurity exhaust in the first divertor campaign of Wendelstein 7-X
T. Kremeyer1, F. Effenberg1, O. Schmitz1, V. R. Winters1, J. Harris2, R. Koenig3,
P. Kornejew3, M. Krychowiak3, D. Zhang3, M. Jakubowski3 and the W7-X Team3
1
University of Wisconsin-Madison, Madison WI 53706 USA
2
Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
3
Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald, Germany
Helium, as the ash of burning D-T plasma, is an unavoidable impurity component in fusion
reactors. Its efficient removal from the confined plasma of a D-T fusion reactor will play a
key role in the path towards achievement of economic fusion power production. The topic
of He exhaust is also embedded into the broader question of light impurity removal, for
instance of such species used for radiative edge cooling [1]. In this presentation, initial
results from impurity gas puff experiments in the first experimental campaign with the
island divertor of Wendelstein 7-X, using He as a tracer element and N2 as well as Ne for
radiative edge cooling, are presented. It is shown that with adjusting the current in the
divertor control coils, the dwell time of these injected impurities can be controlled.
Increased current size yields a decrease of these dwell times, and in general there are two
different time constants involved for the fall of the line emission of the impurities.
These results are obtained by analysis of line emission time traces obtained with a set of
ORNL Filterscopes [2]. They measure the line integrated line emission intensities of
appropriate impurity lines, i.e. He-I 587.4 nm; 667.8 nm; 706.5 nm; 728.1 nm, Ne-I 640.2
nm, N-I 746.8 nm, N-II 500.5 nm. An exponential decay curve was fit to the data which
allowed to measure the effective impurity particle dwell time τp* in the observation domain.
The systematic changes observed are presently investigated by comparison to the detailed
changes in the magnetic structure of the islands in the divertor as response to the increase in
the divertor control coil currents and the emission strength at the measurement location.
Acknowledgements: This work was funded in part by U.S. DoE grant DE-SC0014210.
References
[1] F. Effenberg et al. Nuclear Fusion 57 (2017) 036021
[2] Colchin, R J et al, Rev. Sci. Instrum. 74 (2003)
