Speaker
Tullio Barbui
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1018.pdf
The He/Ne beam diagnostic for active emission spectroscopy in the island
divertor of Wendelstein 7-X
T Barbui1, F. Effenberg1, M. Jakubowski2, R. König2, M. Krychowiak2, S. Loch3, J. Muños
Burgos4, O. Schmitz1 and the W7-X Team2
1
University of Wisconsin, Madison WI, USA
2
Max-Planck-Institute for Plasma Physics, Greifswald, Germany
3
Auburn University, Auburn AL, USA
4
Astro Fusion Spectre, San Diego CA, USA
A dedicated line-ratio spectroscopy system on thermal helium (He) and neon (Ne) was
implemented at Wendelstein 7-X to measure radial profiles of electron density n e(r) and
temperature Te(r) in front of the horizontal target in the graphite island divertor of W7-X.
The injection system consists of two boxes with 5 fast piezo valves each, mounted directly
behind the divertor plates in one upper and one lower divertor module, which are
magnetically connected in the 5/5 island configuration [1]. The new observation system
includes 54 horizontal lines-of-sight which are channelled to a 19cm and a 32cm focal
length Czerny-Turner spectrometer allowing observation of the He and Ne lines as well as
impurities and hydrogen (H) lines with high spectral resolution (dispersion down to 1.3
nm/mm).
In the first divertor campaign of W7-X solely He has been used to measure Te and ne
profiles for the full radial width of the scrape-off layer in the divertor, across the 5/5 island
in the standard magnetic configuration. The spatial resolution of the diagnostic is 3 mm and
the time resolution is 25 ms. Edge parameter measurements with the He-beam have been
carried out during different physics experiments, such as radiative edge cooling and
detachment studies through H fuelling. Preliminary results show clear impact of the seeded
impurities (N2 and Ne) and H fuelling on the measured Te and ne, in agreement with other
edge diagnostics.
Ne has been tested in order to extend the applicability of the diagnostic to the detached
divertor regime at very low Te (≪10eV) to be achieved in the next campaigns. Results from
Ne injection and the status of the development of a dedicated collisional-radiative model for
Ne are here presented.
Acknowledgements: This work was funded in part by the U.S. DoE under grant DE-SC0014210
References
[1] M. Griener et al 2017 Review of Scientific Instruments 88 033509
