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Abstract. MAST is one of the new generation of large, purpose-built Spherical Tokamaks now becoming operational, designed to investigate the properties of the ST in large, collisionless plasmas. The first 6 months of MAST operations have been remarkably successful. Operationally, both merging-compression and the more usual solenoid induction schemes have been demonstrated, the former providing over 400kA of plasma current with no demand on solenoid flux. Good vacuum conditions and operational conditions, particularly after boronisation in trymethylated boron, have provided plasma current of over 1MA with central plasma temperatures (Ohmic) of order 1keV. The Hugill and Greenwald limits can be exceeded, and H-mode achieved at modest additional NBI power. Moreover, particle and energy confinement show an immediate increase at the L-H transition, unlike START where this only became apparent at the highest plasma currents. Halo currents are small, with low toroidal peaking factors, in accordance with theoretical predictions, and there is evidence of a resilience to the major disruption.
IAEA 2001
