MAST accomplishments/plans in support of fusion next-steps

The MAST programme and upgrades are aimed at using MAST´s capabilities and parameter ranges to address specific issues for ITER physics, help find solutions for DEMO (in particular plasma exhaust) and develop a credible physics basis for possible ST-based Component Test Facilities/Fusion Nuclear Science Facilities (CTF/FNSF). MAST is also aimed to provide an attractive access point for scientists and engineers joining fusion. The general approach is to combine experiments, theory and modelling intimately to help create usable predictive models for future devices. Physics results include ELM mitigation with the flexible resonant magnetic perturbation (RMP) coils (up to n=6) where smaller more frequent ELMs are generated. An intriguing aspect is that the profiles with the RMPs active are stable according to 2-D stability codes yet the ELMs are more frequent. This suggests 3-D effects need to be included (3-D distortions and “lobes” are seen in MAST) and probably other physics. Gyrokinetic studies of plasmas perturbed by fuelling pellets show changes that are likely to influence the fuelling efficiency. Instabilities that cause redistribution of fast ions have been avoided by changes in the beam deposition profile (a key element of the upgrades). A major upgrade of MAST has started, a key part of which is devoted to generating many different divertor configurations in the quest to find improved exhaust solutions for DEMO-class devices. Modelling has started of turbulence processes which might enhance cross-field transport to help ease the power handling. The first major phase of the upgrade programme is well underway, to increase the toroidal field and the transformer flux swing and especially implement the flexible exhaust physics platform by means of 17 new poloidal field coils and a closed pumpable divertor. Some of the physics goals and diagnostics described here, and the engineering aspects are described in a companion paper [1].