Energy and Particle Balance Studies Under Full Boron and Lithium‐Coated Walls in TJ‐II

Abstract

The Spanish stellarator TJ-II has been operated under lithium wall conditions for two years so far. Important changes in plasma parameters and, in particular, on particle recycling have been recorded with respect to the normal, boronized wall conditions previously prevailing. The specific effects that the new recycling scenario could have on the improved plasma parameters, and in particular to the global energy balance of electrons and protons are addressed in the present work. In addition, the possible increase in ion energies impinging on the walls should be mirrored by the incoming flux of sputtered lithium atoms. However, a strong decrease of the corresponding sputtering yield is recorded. This effect is analyzed in terms of possible material mixing effects among others.

EMC3-EIRENE modelling of edge plasma and impurity emissions compared with the liquid lithium limiter experiment on EAST

“…Lithium can reduce the fuel recycling via trapping the hydrogen isotopes [6,7], Studies of edge plasma and impurity transport with the toroidally and poloidally localized liquid lithium limiter (LLL) on EAST have been performed by the three-dimensional (3D) edge transport code EMC3-EIRENE. The transport behavior of the Li 1+ and Li 2+ ions shows a non-axisymmetric distribution in the toroidal direction while an axisymmetric distribution is obtained for the Li 3+ ions.…”

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

“…The possible increase in T i (a) values will be directly reflected on the sputtering characteristics of Li from the walls. This point has been addressed in a previous work [10] in terms of global energy balance. No evidence of enhanced peripheral T i under low recycling wall conditions has been found to date.…”

“…Second, a strong reduction of the sputtering yield of Li by plasma particles respect to the expected values from laboratory experiments has been deduced form spectroscopic data [5]. In order to shed some light on the mechanisms responsible for these phenomena, some perturbative experiments were carried out [9,10].…”

Using rational surfaces to improve pellet fuelling in stellarators

“…The NBI system consists of two tangential injectors, one operated in counter configuration, the other in co-counter configuration (E NBI ≤ 32 keV, P NBI ≤ 0.7 MW throughput). Central electron densities and temperatures of n e (0) ≤ 5 × 10 19 m −3 and T e (0) ≤ 400 eV, when a lithium coating is applied to the vacuum vessel wall (Tabarés et al 2010), can be achieved. The central ion temperature, T i (0), achieved with both heating schemes, is ≤∼120 eV.…”