Comparison of hydrogen and tritium uptake and retention in JET

During previous Joint European Torus (JET) deuterium-to-tritium change-over experiments, subdivertor tritium concentrations were compared with those m easured at the strike point region and found to differ significantly during the first few discharges, which was correlated with wall saturation. New d euterium-to-hydrogen fueling experiments in JET have been made and are comp ared to these previous experiments. Rates of hydrogenic species exchange ar e similar to those found in previous tritium experiments. granting differen ces in divertor configuration and mass ratio. In the new experiments, measu rements of the CD and CH molecular band intensities near the divertor strik e point monitor an intermediate stage of particle exchange between the plas ma and wall. The CD/CH ratio correlates well with both the plasma and subdi vertor concentration. The neutral transport code EIRENE and the wall hydrog en trapping and diffusion code WDIFFUSE have been used to evaluate the wall saturation. It appears that chemically-related processes play a role in me diating the plasma-wall exchange. (C) 2001 Elsevier Science B.V. All rights reserved.