MAST is one of the new generation of large, purpose-built spherical tokamaks (STs) now becoming operational, designed to investigate the properties of the ST in large, collisionless plasmas. The first six 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 400 kA of plasma current with no demand on solenoid flux. Good vacuum conditions and operational conditions, particularly after boronization in trimethylated boron, have provided plasma current of over 1 MA with central plasma temperatures (ohmic) of order 1 keV. 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 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.

This paper reports the progress made at JET-ILW on integrating the requirements of the reference ITER baseline scenario with normalised confinement factor of 1, at a normalised pressure of 1.8 together with partially detached divertor whilst maintaining these conditions over many energy confinement time. The 2.5MA high triangularity ELMy H-modes are studied with two different divertor configurations. The power load reduction with N seeding is reported. The relationship between an increase in energy confinement and pedestal pressure with triangularity is investigated. The operational space of both plasma configurations is studied together the ELM energy losses and stability of the pedestal of unseeded and seeded plasmas.

The dependences of energy confinement on plasma current and toroidal magnetic field have been investigated in the MAST spherical tokamak in H-mode plasmas. Multivariate fits show that the dependence of energy confinement time on plasma current Ip is weaker than linear while the dependence on toroidal magnetic field BT is stronger than linear, in contrast to conventional energy confinement scalings. These Ip and BT dependences have also been confirmed by single parameter scans. Transport analysis indicates that the strong BT scaling of energy confinement could possibly be explained by weaker q and stronger ν* dependence of heat diffusivity in comparison with conventional tokamaks.

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High triangularity regimes, approaching double null, have become more important recently. H-mode access and edge stability are affected by the close proximity of the second X-point to the last closed flux surface, but more experimental evidence is needed. Inter-machine comparisons of MAST with ASDEX Upgrade (AUG) and NSTX confirm the reduction of the H-mode power threshold in the true double null configuration (C-DN), first reported on MAST. A more negative radial edge electric field in L-mode observed on MAST and ASDEX Upgrade may be connected to the improved H-mode access. About twice the power density is needed on MAST to achieve edge pressures similar to AUG in L-and H-modes. However, on MAST the pressure is dominated by the edge density in H-mode. So far, in single null (SN) ELMs have not been observed on MAST with neutral beam heating powers P NBI 2 MW, due to the different edge profiles in SN H-mode. This is supported by the modelling of the stability of the measured edge profiles against ideal peeling-ballooning.