Divertor shaping with neutral baffling as a solution to the tokamak power exhaust challenge

TL;DR

This study demonstrates that long-legged divertors with high magnetic flux expansion effectively reduce heat loads and improve power exhaust in tokamaks, offering a feasible design approach for fusion reactors.

Contribution

It provides experimental evidence that strategic divertor shaping, including long-legged designs and neutral baffling, enhances power exhaust without compromising core performance.

Findings

Long-legged divertors reduce target heat loads.

Flux expansion improves detachment stability.

Neutral baffling enhances power exhaust efficiency.

Abstract

Exhausting power from the hot fusion core to the plasma-facing components is one of the biggest challenges in fusion energy. The MAST Upgrade tokamak uniquely integrates strong containment of neutrals within the exhaust area (divertor) with extreme divertor shaping capability. By systematically altering the divertor shape, this study shows the strongest evidence to date that long-legged divertors with a high magnetic field gradient (total flux expansion) deliver key power exhaust benefits without adversely impacting the hot fusion core. These benefits are already achieved with relatively modest geometry adjustments that are more feasible to integrate in reactor designs. Benefits include reduced target heat loads and improved access to, and stability of, a neutral gas buffer that 'shields' the target and enhances power exhaust (detachment). Analysis and model comparisons shows these benefits are obtained by combining multiple shaping aspects: long-legged divertors have expanded plasma-neutral interaction volume that drive reductions in particle and power loads, while total flux expansion enhances detachment access and stability. Containing the neutrals in the exhaust area with physical structures further augments these shaping benefits. These results demonstrate strategic variation in the divertor geometry and magnetic topology is a potential solution to one of fusion's biggest challenges: power exhaust.