Confinement transitions in TJ-II under Li-coated wall conditions

This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma– wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 10 19 m −3 and Te ≈ 250–300 eV, with peaked density, rather flat Te profiles and higher ion temperatures. Due to the achieved