First results from MAST

MAST is one of the new generation of large, purpose-built spherical tokamak s (STs) now becoming operational, designed to investigate the properties of the ST in large, collisionless plasmas. The first six months of MAST opera tions have been remarkably successful. Operationally, both merging-compress ion and the more usual solenoid induction schemes have been demonstrated, t he former providing over 400 kA of plasma current with no demand on solenoi d flux. Good vacuum conditions and operational conditions, particularly aft er boronization in trimethylated boron, have provided plasma current of ove r 1 MA with central plasma temperatures (ohmic) of order I keV. The Hugill and Greenwald limits can be exceeded and H mode achieved at modest addition al NBI power. Moreover, particle and energy confinement show an immediate i ncrease at the L-H transition, unlike the case of START, where this became apparent only 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.