Tritium Enrichment in the JET Divertor and its Relation to Tritium Uptake and Retention

Future fusion reactors, like ITER, will rely on an active exhaust system to pump tritium (T) in the divertor and then recirculate it to the fuel stream. Estimation of the T inventory requires a detailed T balance, which determines if T is preferentially enriched relative to D in its pathway from the main plasma to the divertor and pump. On the Joint European Torus (JET), the neutral T concentration in the sub-divertor (pumping plenum and region below the divertor strike point plate) is measured with a modified Penning gauge coupled to a high-resolution spectrometer. In addition, T concentration measurements are made in the plasma edge and strike point region with a spectrometer viewing these regions. The sub-divertor and divertor (region above the strike point plate) T concentration measurements show differences during initial T uptake and retention which are characteristic of wall deposition properties. Since wall retention is one of the factors in calculating the eventual T inventory in a reactor, a detailed study of this process has been undertaken.