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(EX/S1-6) Stability at High Performance in the MAST Spherical Tokamak

R.J. Buttery1), R. Akers1), E. Arends2), N.J. Conway1), G. Cunningham1), C.G. Gimblett1), M. Gryaznevich1), R.J. Hastie1), M.J. Hole1), I. Lehane1), R. Martin1), A. Patel1), T. Pinfold1), O. Sauter3), D. Taylor1), G. Turri1), M. Valovic1), M.J. Walsh4), H.R. Wilson1), MAST Team 1)
1) EURATOM/UKAEA Fusion Association, Abingdon, United Kingdom
2) FOM Instituut voor plasmafysica “Rijnhuizen”, Nieuwegein, The Netherlands
3) CRPP, Association EURATOM-Confédération Suisse, EPFL, Lausanne, Switzerland
4) Walsh Scientific Ltd., Culham Science Centre, Abingdon, Oxon, UK

Abstract.  The new generation of Spherical Tokamaks (STs) provides the first opportunity to examine stability properties in power-plant-relevant low collisionality regimes. This can help assess the ST’s potential as a route to fusion power, but also provides crucial tests of stability physics used in extrapolation to devices such as ITER. On MAST, the first identification of neoclassical tearing modes in the ST has been made. Behaviour is remarkably well described by existing theory, confirming predictions for key physics parameters. Analysis highlights the significance of stabilising field-curvature effects, suggesting a new route for avoidance of these modes. Stable operation has been demonstrated at high normalised beta of $ \sim$4.5 ( $ \sim$ 5li), illustrating the favourable stability properties and high beta potential of the ST. q=1 `snake' phenomena exist through sawtooth trains, with studies providing key tests of sawtooth physics models. Disruption/reconnection behaviour is also being explored. These exciting studies are being pushed even further in 2002, with a near doubling of auxiliary heating power and new diagnostics commissioned, including 300 point and multi-time Thomson scattering systems.

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IAEA 2003