Material Erosion and Redeposition During the JET MkII GB-SRP Divertor Campaign

This contribution provides an overview of experimental results obtained in the area of material erosion and migration during the JET operational campaigns 2002-2004 (C5-C14) with the MkIIGB-SRP divertor configuration and summarises recent modelling activities aimed at understanding these data. Post-mortem analysis of a poloidal tungsten stripe deposited prior the campaigns in the divertor reveals in agreement with previous results that the inner divertor is deposition dominated with maximum layer thicknesses up to 300mm whereas the outer divertor is erosion dominated in the average over the campaigns. Detailed SEM analysis shows that the outer divertor erosion occurs non-uniformly on a scale length of 10-30mm. Shot-resolved deposition/erosion measurements with a Quartz MicroBalance (QMB) mounted in the inner divertor louver region demonstrate that the inner strike point position is the most important parameter for the deposition on the QMB with increasing deposition moving the strike point down the vertical target and largest deposition when the strike point is located on the base plate. Data with the strike point on the base plate show a significantly larger deposition in H-mode than in L-mode discharges (about a factor of 20) while this difference is not clearly pronounced with the strike point on the vertical target.13CH4 injection through the outer divertor during identical H-mode discharges showed about 75% of the measured 13C deposition on the outer divertor tiles but also a significant transport of 13C to the inner divertor and the main chamber region.
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