Overview of material re-deposition and fuel retention studies at JET with the Gas Box divertor

TLDR

During 1998–2001 the JET tokamak operated with the MkII Gas Box divertor, and the study discusses material migration processes and how operation scenarios affect deposit morphology. The study aimed to determine erosion and deposition patterns to evaluate material erosion, migration, and fuel inventory on plasma‑facing components. Limiter and divertor tiles were retrieved twice and examined ex situ with surface‑sensitive techniques, while tracer methods—including 13C‑methane injection and low‑Z/high‑Z marker layers—were employed to enhance information on material transport. Results revealed a pronounced asymmetry between inner deposition and outer erosion divertor channels, no significant highly hydrogenated carbon films in the Gas Box, and comparisons with earlier divertor campaigns.

Abstract

In the period 1998—2001 the JET tokamak was operated with the MkII Gas Box divertor. On two occasions during that period a number of limiter and divertor tiles were retrieved from the torus and then examined ex situ with surface sensitive techniques. Erosion and deposition patterns were determined in order to assess the material erosion, material migration and fuel inventory on plasma facing components. Tracer techniques, e.g. injection of 13C labelled methane and tiles coated with a low-Z and high-Z marker layer, were used to enhance the volume of information on the material transport. The results show significant asymmetry in the distribution of fuel and plasma impurity species between the inner (net deposition area) and the outer (net erosion) divertor channels. No significant formation of highly hydrogenated carbon films has been found in the Gas Box structure. The important processes for material migration, and the influence of operation scenarios on the morphology of the deposits are discussed. Comparison is also made with results obtained following previous divertor campaigns.