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Experimental results obtained on the divertor tokamak ASDEX are combined with theoretical computer simulations to characterise the edge plasma during discharges heated solely by the plasma current. Special attention is given to particle fluxes and transport in the plasma edge. In this context, the difference in edge behaviour between hydrogen and deuterium discharges is of significance. The various release mechanisms for metallic and non-metallic impurities are described. Profiles of a variety of impurity ions in the plasma edge are calculated, with emphasis on beryllium, a limiter material which has been used with success in UNITOR and in JET. Finally, optimised discharge scenarios are investigated, in which ohmic discharges with high particle densities show enhanced confinement. Both in the Improved Ohmic Confinement (IOC) regime, first discovered in ASDEX, and in the raising of particle density by pellet injection, the recycling within the edge plasma plays a decisive part in creating sharp-pointed radial profiles of electron density in the tokamak plasma; these, in turn, are associated with very good transport characteristics. Under such conditions, both global particle confinement and global energy confinement are significantly increased.

Additional information

Authors: BESSENRODT-WEBERPALS M, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/256 DE (1990) 122 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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