The lithium wall stellarator experiment in TJ-II

In the last years, lithium wall conditioning has been carried out in several fusion devices by different techniques, providing in many instances record values of plasma parameters and enhanced plasma reproducibility and opening the possibility of developing high radiative, low recycling liquid divertor concepts of high potential for future reactors. This concept has been termed the Li Tokamak Reactor. Compared to tokamaks, stellarator plasmas show distinct features in their interaction with the surrounding materials. The lack of disruptions and type I ELMs make them more reliable for reactor operation. So it is the lack of MHD-driven density limit. On the other side, the intrinsic radiative character of the density limit of stellarators and the tendency to central impurity accumulation makes wall-material selection paramount. In the present work, the plasma performance of the TJ-II Heliac under Li-coated wall conditions is described. Compared to previous coatings, lithium has produced the best plasma performance to date, leading to the achievement of record values in plasma density and energy confinement. Plasma profiles free from impurity accumulation have been obtained under specific fuelling schemes. The development of L-H transitions has been characterized in terms of steep gradients in edge parameters and broadband fluctuation suppression. (author)