Stabilizing Fusion Plasma with 3D Magnetic Coils
In a landmark achievement, scientists at the UK Atomic Energy Authority (UKAEA) have successfully used small magnetic coils to apply a 3D magnetic field, stabilizing plasma instabilities in a spherical tokamak for the first time. This breakthrough, accomplished during the fourth scientific campaign of the Mega Amp Spherical Tokamak (MAST) Upgrade, marks a significant step toward sustainable fusion energy.
Fusion fuel in MAST Upgrade is confined at high temperatures to create plasma. However, high plasma current, pressure, or density can lead to instabilities, reducing performance or risking damage to tokamak components. Edge Localised Modes (ELMs), instabilities at the plasma edge, pose a challenge to fusion power plant components. Using Resonant Magnetic Perturbation (RMP) coils, researchers achieved complete ELM suppression, a world-first for spherical tokamaks.
“Suppressing ELMs in a spherical tokamak is a landmark achievement. It is an important demonstration that advanced control techniques developed for conventional tokamaks can be successfully adapted to compact configurations to develop the scientific basis for future power plants like STEP,” said James Harrison, Head of MAST Upgrade Science at UKAEA.
Advancements in Plasma Exhaust Management
Another world-first achievement involves independent control of plasma exhaust in the upper and lower divertors of MAST Upgrade without affecting the main plasma chamber’s performance or density. The divertor system directs particles and heat from the plasma onto tokamak surfaces, a critical challenge in fusion energy. This independent control enhances the flexibility and robustness of future fusion power plants.
Additionally, experiments with nitrogen injection at the plasma edge have shown that energy can be evenly distributed across plasma-facing components, preventing excessive heat buildup. This technique aligns compact spherical tokamaks with advanced exhaust solutions used in conventional tokamaks.
Record-Breaking Plasma Performance and Shaping
MAST Upgrade set a new record by injecting 3.8 megawatts of power into its plasma using neutral beam heating, supporting higher-performance plasma scenarios. The campaign also achieved the best plasma shape ever recorded in the machine, with an elongation of 2.5 (plasma height 2.5 times its width). This shaping enhances plasma stability, enabling higher pressure and better confinement, critical for future fusion power plants like STEP.
Implications for Future Fusion Energy
These breakthroughs reinforce the UK’s leadership in fusion research. The results will inform the design of ELM control systems for the Spherical Tokamak for Energy Production (STEP) program and help eliminate ELMs as a barrier to commercial fusion viability. Further experiments are planned to expand on these findings.
“I’m delighted with the ground-breaking findings from our team at UKAEA. These achievements reinforce the UK’s leadership in fusion research and bring us closer to realizing fusion as a clean, safe, and abundant energy source for the future,” said Fulvio Militello, Executive Director of Plasma Science and Fusion Operations, UKAEA.