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15th International Conference on Plasma Surface Interactions in Controlled Fusion Devices (PSI 15), Gifu, 2002-05-26 to 2002-05-31
Abstract:
A campaign of pure helium discharges in the JET tokamak equipped with the MarkIIGB divertor
has been performed. This paper describes some of the experimental observations of divertor
detachment obtained in L-mode density ramp He discharges and presents a selection of results from
the application of B2.5-Eirene code modelling to a JET He plasma. Detachment is very different
from that observed in equivalent D discharges. Particle fluxes remain attached up to higher densities
and, with decreasing input power, particle detachment occurs earlier in density. However, in
contrast to comparable D plasmas, the low measured target Te at all but the lowest ne in helium
leads to an earlier decrease in power flux. Simulations show that detachment is caused by the
escape of He neutrals from the target vicinity where, together with the He+ ions they radiate along
the separatrix and above the X-point area, starving regions downstream of power.
