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(EX/C2-6) H-mode Access Physics in MAST

P.G. Carolan1), A.R. Field1), H. Meyer1), C.D. Challis1), G. Cunningham1), A. Kirk1), M. Valovic1), R. Akers1), A. Arends2, P.J. Catto3), N.J. Conway1), G.F. Counsell1), S.J. Fielding1), T. Fülöp4, P. Helander1), P.B. Jones5), B. Lloyd1), M. McGrath6), A. Patel1), A. Sykes1), D.M.A. Taylor1), M.R. Tournianski1), M.J. Walsh7), H.R. Wilson1)
1) UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, United Kingdom
2) FOM Institut voor Plasmafhysica Rijnhuizen, Niewwegein, Netherlands
3) Plasma Science and Fusion Centre, Massachusetts Institute of Technology, Cambridge, MA, USA
4) Dept of Electromagnetics, Chalmers University of Technology, Göteborg, Sweden
5) Imperial College of Science, Technology and Medicine, London, UK
6) University College, Dublin, Ireland
7) Walsh Scientific Ltd., Culham Science Centre, Abingdon, Oxon, UK

Abstract.  Spherical tokamaks offer extreme plasma parameters for scalings and model testing whilst also accessing plasma regimes of interest to conventional tokamaks. The cross-section of MAST is similar to medium sized tokamaks allowing comparisons of confinement, stability and transport, and thus helping to remove some degeneracies, for example, in H-mode power threshold scaling. Extensive diagnostic systems, e.g. 300 point Thomson scattering, provide detailed monitoring of the edge and SOL regions, and in H-mode plasmas, showing increases in particle and energy confinement and steepening of edge gradients. In addition, a reduction in turbulence was observed, together with a sharp increase in the Electron Bernstein Wave emission cone and rapid acceleration of edge poloidal flow. The operating window for reliable H-mode access has been greatly extended by the use of inboard refuelling, whilst also providing high reproducibility, and with Connected Double Null Divertor operation, reduces the power threshold to levels now consistent with the latest international power law scalings. Confinement for low frequency Type III ELMs is also in agreement with the international scaling law IPB(y,2).

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IAEA 2003