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          Institute: MPI für Plasmaphysik     Collection: Articles, Books, Inbooks     Display Documents

ID: 21071.0, MPI für Plasmaphysik / Articles, Books, Inbooks
Transport into and across the scrape-off layer in the ASDEX Upgrade divertor tokamak
Authors:Neuhauser, J.; Coster, D.; Fahrbach, H. U.; Fuchs, J. C.; Haas, G.; Herrmann, A.; Horton, L. D.; Jakobi, M.; Kallenbach, A.; Laux, M.; Kim, J. W.; Kurzan, B.; Müller, H. W.; Murmann, H.; Neu, R.; Rohde, V.; Sandmann, W.; Suttrop, W.; Wolfrum, E.; ASDEX Upgrade Team
Date of Publication (YYYY-MM-DD):2002
Title of Journal:Plasma Physics and Controlled Fusion
Journal Abbrev.:Plasma Phys. Control. Fusion
Issue / Number:6
Start Page:855
End Page:869
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:The elements of transport into and across the scrape-off layer in the poloidal divertor tokamak ASDEX Upgrade are analysed for different operational regimes with emphasis on enhanced confinement regimes with an edge barrier. Utilizing the existing set of edge diagnostics, especially the high- resolution multi-pulse edge Thomson scattering system, in combination with long discharge plateaus, radial sweeps and advanced averaging techniques, detailed radial mid-plane profiles of diverted plasmas are obtained. Profiles are smooth across the separatrix, indicating strong radial correlation, and there is no remarkable variation across the second separatrix either. Together with measured input, recycling, pumping and bypass fluxes, a corrected separatrix position is determined and transport characteristics are derived in the different radial zones generally identified in the profile structure. Transport in the steep gradient region inside and across the separatrix shows typical ballooning-type critical electron pressure gradient scaling and, in parallel, even a clear correlation between radial electron density and temperature decay lengths (e.g. eta(e) = d(ln T)/d(ln n) similar to 2 for type-I ELMy H-modes). These findings indicate the importance of stiff profiles in this region, while diffusion coefficients are secondary parameters, determined essentially by the source distribution. The outer scrape-off layer wing exhibits a more filamentary structure with preferential outward drift especially in high-performance discharges, with formal diffusion coefficients far above the Bohm value in agreement with results on the old ASDEX experiment. A basic mechanism involved there seems to be partial loss of equilibrium and fast curvature-driven outward acceleration, in principle well known from theory, investigated decades ago in pinch experiments and utilized recently in high- field-side pellet fuelling.
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Plasmaphysik/Tokamak Scenario Development (E1)
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