Analyses of deuterium retention in tungsten and graphite first wall materials by laser-induced ablation spectroscopy on EAST

Abstract

• Combined LIBS and LIAS measurements were applied to determine the dynamic deuterium retention in C and W during EAST discharges. • LIAS measurements show more than three times higher deuterium retention in graphite than in tungsten during EAST discharges. • The deuterium retention on the graphite PFC is saturated within 0.2 s plasma exposure for limited magnetic configuration when the plasma actively touches the first wall. • The deuterium retention in the start-up phase is significantly larger than during the discharge for diverted magnetic configuration. Plasma-wall interactions at the first wall in fusion experimental devices are critical for the life time of plasma-facing components and tokamak operation. In-situ measurements of these plasma-wall interaction processes are required in long pulse devices in order to understand better the underlying mechanisms as well as monitoring of the tritium content of the first wall as an immediate safety application. In this work we present measurements of the deuterium retention in the first wall of EAST using laser-induced ablation spectroscopy. The diagnostic is applied during plasma operation and the dynamic retention for graphite and tungsten as plasma-facing materials are compared, showing more than three times higher short-term retention in graphite than in tungsten. Laser-based analysis is applied during a shift of the vertical positions of the plasma column in limited as well as in the start-up phase of discharges in diverted magnetic configuration. Plasma core densities of n e = (1.5–3.2) × 10 19 /m 3 are chosen to vary the ion flux to the first wall and study saturation effects of deuterium on the surface first wall materials during tokamak plasma operation. A linear dependence of the retention from ion fluence is observed for graphite as PFC up to 3 × 10 18 D + /cm 2 , followed by a constant retention up to fluences of 3.5 × 10 19 D + /cm 2 for nearby first wall temperatures of T PFC ≈ 350 K.