Overview of physics results from MAST

Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities P _NBI ≤ 3.8 MW H-mode at I_p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I_p and more strongly with B_t than in the ITER IPB98(y, 2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original designed total throughput capacity. The anomalous momentum diffusion, χ_φ, is linked to the ion diffusion, χ_i, with a Prandtl number close to P_φ ≈ χ_φ/χ_i ≈ 1, although χ_i approaches neoclassical values. New high spatial resolution measurements of the edge radial electric field, E_r, show that the position of steepest gradients in electron pressure and E_r (i.e. shearing rate) are coincident, but their magnitudes are not linked. The T_e pedestal width on MAST scales with √β_pol^ped rather than ρ_pol. The edge localized mode (ELM) frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of four external coils (n = 1, 2). A new internal 12 coil set (n ≤ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes. Fast particle instabilities also affect the off-axis NBI current drive, leading to fast ion diffusion of the order of 0.5 m ² s^-1 and a reduction in the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a ST generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST.