Recycling and sputtering studies in hydrogen and helium plasmas under lithiated walls in TJ-II

Lithium sputtering has been studied in TJ-II under lithiated walls. The measured sputtering yield in H plasmas was found to be significantly lower than that expected from laboratory experiments and TRIM code calculations. Moreover, the dependence of that yield on edge temperature is consistent with an energy threshold much larger than that of pure lithium. The effect of material mixing, candidate for the observed behaviours was studied by means of boron coating of the Li layer. Also the particle retention and release under H/He plasmas in this very low recycling scenario was investigated. Recycling coefficients R < 0.1 and r ∼ 0.85 for H and He, respectively, were measured. The release of either species in the opposite plasma was studied for several plasma conditions and in GD plasmas.