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The JET Team1 (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
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.
IAEA 2001
