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P: Plasmaphysik

P 19: Plasma Physics

P 19.3: Vortrag

Freitag, 21. März 2003, 11:10–11:30, FO2

Transport barrier formation on the MAST spherical tokamak — •Anthony Field, Clive Challis, Neil Conway, Geoffrey Cunningham, Hendrik Meyer, and Per Helander — EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK

Operation under improved confinement regimes is crucial to the viability of a future fusion power plant. In such regimes the transport of energy and particles can be reduced to levels comparable to the underlying neo-classical, collisional transport by shear-flow decorrelation of turbulence.

On MAST access to H-mode, in which a transport barrier forms spontaneously at the plasma edge, is favoured by inboard gas puff refuelling, during which increased flow is observed at the outboard plasma boundary. These observations are consistent with the predictions of neo-classical theory, extended to account for neutral viscosity.

’Internal’ transport barriers can also be produced by sheared flow driven by momentum input from the neutral beam heating. On MAST, NBI heating of plasmas with weak magnetic shear has produced ITBs, primarily in the ion channel. Simulations indicate that inside the ITB ion thermal and momentum diffusivities are of the same order as given by neo-classical theory. This supports the curious prediction: whereas thermal transport is strongly enhanced by trapped particles in the banana regime, momentum transport is not.

This work is funded jointly by the UK Department of Trade and Industry and EURATOM.