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(EX6/4) Recent Results from Divertor and SOL Studies at JET

   
The JET Team ¹ (presented by R. D. Monk )
¹ see Appendix to IAEA-CN-69/OV1/2
 
JET Joint Undertaking, Abingdon, Oxfordshire, United Kingdom

Abstract
Recent progress in the study of divertor and scrape-off layer plasma (SOL) phenomena in JET  is reviewed. Up to the present time, three pumped divertors (Mark I, Mark IIA/AP and Mark IIGB) have been installed and exploited under reactor relevant conditions. With increased divertor closure, it is found that the particle exhaust rate has increased and neutral compression factors of $>$ 100 are obtained with the Mark IIGB divertor. Helium enrichment factors of $>$ 0.2 are measured under a wide range of conditions and satisfy the minimum requirements for ITER . Fast infra-red camera measurements show broad deposition profiles during type I ELMs  and energy densities of $\rm\sim 0.12MJm^{-2}$. During the recent D-T experiments, the codeposition of tritium on cold shadowed surfaces in the inner divertor has been identified as an important form of long-term tritium retention. This has serious implications for the divertor design and tritium inventory in a next-step tokamak. Core plasma purity has not improved with enhanced divertor closure or decreased main chamber neutral pressure. Studies of the chemical sputtering yield have shown a dependence on surface temperature and hydrogen isotope. This accounts for the observation of increased impurity production and lower disruptive density limits in Mark II (at 500K) compared to Mark I (at 300K). Significant progress has been made in the study of divertor detachment , and volume recombination has been spectroscopically identified. With increasing isotope mass, detachment and the disruptive density limit  occur at lower main plasma density as predicted by the EDGE2D/NIMBUS codes. Using differential gas fuelling in the Mark IIGB divertor, it has been possible to modify the in-out asymmetry of the divertor plasma for the first time.

     

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