Impurity accumulation is considered to be a crucial issue in the path towards a fusion-grade stellarator reactor. The reason is that stellarator operation scenarios usually display a negative radial electric field that, according to standard neoclassical theory, should cause an inwards impurity pinch roughly proportional to the charge number Z. This impurity accumulation is observed …
Three running stellarators are available in the frame of the present project for planning, running and analysis of experiments: TJ-II at CIEMAT, in Spain; the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS), in Japan; and the Wendelstein 7-X (W7-X) stellarator, at the Max-Planck Institute for Plasma Physics (IPP) in Germany. …