Properties of vacuum-deposited Li films and impact on plasma performance in TJ-II

Abstract

Drastic changes in the operation of the Spanish TJ-II stellarator have been produced upon lithiation of its first wall in 2007, performed by direct vacuum evaporation. From the operational point of view, much more stable, reproducible plasmas have been achieved, mostly due to the excellent density control associated with the low recycling wall characteristics. It has allowed exploring new, high densities, high power plasma conditions never attained under the previous, boron coating scenarios. In addition to this, new physical phenomena arose. Thus, for example, clear transitions to enhanced confinement modes (H mode) and strongly peaked plasma profiles were observed under the new wall conditions. In this paper, a summary of the main findings is described, and recent results on the interchange of plasma species (H vs. He) and sputtering in the Li wall are described and discussed.