MAST Accomplishments and Upgrade for Fusion Next-Steps

Abstract

The Mega Amp Spherical Tokamak (MAST) program and a major upgrade are aimed at using MASTs 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. MAST also provides an attractive access point for scientists and engineers joining fusion. The general approach is to combine experiments, theory, and modeling intimately to help create usable predictive models for future devices. Physics results include edge-localized mode (ELM) mitigation with the flexible resonant magnetic perturbation coils (up to n=6), where smaller, more frequent ELMs are generated, challenging conventional 2-D stability theory. Gyrokinetic theory and models are combined with experiments in the areas of pedestal stability, pellet fueling optimization, and impurity transport. Fast particle stability and confinement are used to optimize scenarios and neutral beam geometry. Exhaust modeling includes turbulence processes that enhance cross-field transport to help ease the power handling. The first major phase of the upgrade program is well under way, 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. Changes in the neutral beam systems (off-axis as well as on-axis) and new diagnostics especially of the divertor complete the present upgrade scope.