Speaker
Thomas Wegner
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1112.pdf
First Results of Transport Studies of injected impurities in
Wendelstein 7-X
Th. Wegner1 , B. Geiger1 , R. Burhenn1 , F. Kunkel1 , B. Buttenschön1 , A. Langenberg1 ,
N. Pablant2 , P. Traverso3 , D. Zhang1 and the W7-X Team1
1 Max-Planck Institute for Plasma Physics, Greifswald, Germany
2 Princeton Plasma Physics Laboratory, Princeton, NJ, USA
3 Auburn University, Auburn, AL, USA
This contribution explains in detail the experimental setup of the new laser blow-off system on
W7-X and presents initial results regarding transport properties of injected impurities which
were introduced in plasmas with different conditions.
The understanding of impurity transport is a demanding task for stellarators which have a
high potential for steady state operation. The accumulation of impurities in confined plasma in
certain operation regimes can cause an early pulse termination due to a radiative collapse. The
development of favorable operating scenarios that avoid these accumulations is therefore one
of the main objectives of W7-X operation. Hence, the investigation of transport properties is
inevitable and a new laser blow-off system was installed to inject non-intrinsic, non-recycling
impurities in a controlled manner. The system was available from the beginning of the second
operation phase OP1.2a and successfully performed more than 300 injections of different mate-
rials with varying material thicknesses, spot diameters and injections frequencies. The ablated
amount was large enough to measure the emission of several ionization stages from the X-ray
to XUV wavelength range with temporal and spatial resolution in different magnetic field con-
figurations and plasma parameters. From the temporal decay of the emission one can estimate
a confinement time of the injected impurities of about 100 ms. The detailed analysis of the
emission by means of the radiation and transport code STRAHL enables the characterization of
transport properties, e.g., diffusion and convection coefficient.
