Harnessing fusion energy efficiently requires optimising heat and particle
exhaust in the edge from the fusion core plasma, which can be achieved through
magnetic shaping of the divertor into Alternative Divertor Configurations
(ADCs). In this study, we leverage MAST-U's unique shaping capabilities, which
allow for a ∼×2 variation in the ratio of the magnetic field at the
X-point and target (Bxpt​/Bt​), to investigate the power exhaust and
core-edge compatibility of ADCs.
Experiments show ADCs with large Bxpt​/Bt​ ratios drastically enhance
divertor performance, with heat and particle loads reduced by factors up to
∼20 and a 120 \% reduction in detachment onset. Notably, these benefits
are achieved without compromising core plasma conditions.
Our analysis attributes these improvements to the extra volume available
below the ionisation front in longer leg-length divertors. This facilitates
power dissipation and reduced particle loads through ion sinks from atomic
(Electron-Ion Recombination) and molecular (Molecular-Activated Recombination)
processes. The onset of divertor detachment and the evolution of the detachment
front agrees with analytic models and divertor exhaust simulations.
These insights emphasise the potential minor divertor geometry adjustments
can have on power exhaust. This study illuminates pathways for devising
optimised exhaust strategies in future fusion devices