MAST: Results and upgrade activities

MAST, alongside other spherical tokamaks (STs), provides new perspectives on tokamak physics for ITER and beyond, and a platform to explore the potential of the ST as the core of a Component Test Facility (CTF) to test and develop components and technology for fusion power plants. MAST is one of the two largest STs in the world, the other being NSTX (PPPL, US). Recent physics results include new measurements of the edge pedestal, the use of magnetic perturbations to influence ELMs, pellet fuelling, H-mode access, core transport, confinement scaling, fast particle physics and MHD instabilities. The programme makes use of a set of unusually high resolution and wide-viewing diagnostics on MAST, since in all experiments the focus is on understanding the mechanisms, to support predictive modelling and comparison with other types of tokamak. The first stage of a major upgrade is under way which will raise the heating power and toroidal field by 50% and almost double the inductive flux swing to allow long pulses and sustained non inductively driven plasmas. In particular 17 poloidal field coils and an in-vessel cryo-pump will be added, to allow an expanded divertor based on the "super-X" concept as well as a conventional configuration. These upgrades will transform the operating space, pulse length and flexibility of MAST for goal-oriented research and as a user facility. The heating and pulse length upgrades will allow stringent tests of off-axis current drive and fast particle effects (important for sustained tokamak fusion plasmas), and the development of steady state scenarios for a CTF. The divertor development is part of a growing international effort to find solutions for the power exhaust which minimise the technology and materials advances needed for the divertor plasma facing components in a fusion power plant.