Speaker
Andreas Langenberg
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.118.pdf
Impurity Transport Studies at Wendelstein 7-X by Means of X-ray Imaging
Spectrometer Measurements
A. Langenberg1, N.A. Pablant2, A. Dinklage1, Th. Wegner1, P. Traverso3, O. Marchuk4,
B.Geiger1, B. Buttenschön1, C. Brandt1, H. Thomsen1, M. Kubkowska5, A. Czarnecka5,
S. Jabłoński5, U. Neuner1, N. Tamura6, J.L. Valesco7, J.A. Alonso7, A. Mollén1, D. Zhang1,
R. Burhenn1, R.C. Wolf 1 and the W7-X team
1
Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
2
Princeton Plasma Physics Laboratory, Princeton, NJ, USA
3
Auburn University, Auburn, Alabama, USA
4
Institut für Energie und Klimaforschung-IEK-4, Forschungszentrum Jülich, 52425 Jülich, Germany
5
Institute of Plasma Physics and Laser Microfusion, Hery 23 St. 01-497 Warsaw, Poland
6
National Institute for Fusion Science, 322-6, Oroshi-cho, Toki-City, Gifu 509-5292, Japan
7
Laboratorio Nacional de Fusión, Asociación EURATOM-CIEMAT, Madrid, Spain
Due to non axis symmetric 3D magnetic fields, impurity transport in the hot plasma core in
stellarators is fundamentally different to tokamaks. In view of reactor-like operation,
understanding the impurity transport is a prerequisite for steady-state operation. These aspects
motivate initial impurity transport studies in W7-X at previously - in optimized stellarators –
unexplored, reactor-relevant collisionalities. New effects, like potential variations on flux-
surfaces [1] or screening effects due to species dependent transport regimes [2] are examples
for aspects which attracted recent interest. Spatio-temporal impurity emissivities were
measured by the x-ray imaging spectrometers XICS [3] and HR-XIS [4], optimized to detect
He-like impurity emission. These spectrometers provide measurements of the radial electric
field [5] and also allow for a direct determination of diffusive and convective transport
parameters D and v [6]. Therefore, impurity transport in various stellarator specific transport
regimes can be studied. In this paper, a systematic parameter scan varying the electron
cyclotron resonance (ECR) heating power and the electron density ne has been carried out.
Furthermore, the specific settings of the power deposition reveal a significant impact on
impurity confinement time, possibly driven by changes in the radial electric field at very low
collisionalities – uniquely addressable in large stellarators like W7-X. Experimental findings
are compared to neoclassical theory [7] and modeled with the 1D transport analysis code
STRAHL. The study aims to reveal the impact of aspects entering stellarator optimization
(e.g. ripples, magnetic mirrors) on the impurity fluxes.
[1] J.M Garcia-Regana et al, Nucl. Fusion 57, 056004 (2017)
[2] P. Helander et al., Phys. Rev. Lett. 118, 155002 (2017)
[3] N.A. Pablant, M. Bitter, R. Burhenn et al. 41st EPS conference on Plasma Physics Berlin (2014)
[4] G. Bertschinger, W. Biel, H. Jaegers, and O. Marchuk, Rev. Sci. Instrum. 75 3727 (2004)
[5] N.A. Pablant, A. Langenberg, S. Satake et al. 43rd EPS conference on Plasma Physics Leuven (2016)
[6] A. Langenberg, N.A. Pablant, O. Marchuk et al. Nucl. Fusion 57 086013 (2017)
[7] A. Mollén, S. Newton, P. Helander et al. 21st Int. Stellarator Workshop, Kyoto, (2017) (invited)
