Scientists at the UK Atomic Energy Authority’s (UKAEA) Culham Science Centre have achieved a world-first in plasma control using the MAST Upgrade spherical tokamak. In a series of experiments, the team successfully deployed a set of 18 specialized magnetic coils to apply resonant magnetic perturbations (RMPs), actively steering the plasma exhaust to manage the intense heat flux striking the device’s divertor. This technique addresses a critical engineering challenge for future fusion power plants, where unmitigated heat loads can rapidly damage plasma-facing components. According to UKAEA lead scientist Dr. Andrew Kirk, this result provides a potential solution for controlling the immense power exhaust anticipated in commercial-scale reactors. Source: UKAEA

The experiment's success lies in the precise manipulation of the plasma edge. RMPs are small, externally applied 3D magnetic fields that intentionally break the axisymmetric nature of the primary tokamak confinement field. By doing so, they can spread the narrow stream of heat and particles flowing out of the core plasma over a much wider area of the divertor plates. This prevents the formation of hotspots where temperatures could otherwise exceed material limits. Managing this power exhaust is a major focus for next-generation devices like ITER, which must handle steady-state heat loads far exceeding those in current experiments, with projections reaching up to 10 megawatts per square metre. Source: UKAEA

RMPs are small, externally applied 3D magnetic fields that intentionally break the axisymmetric nature of the primary tokamak confinement field.

MAST Upgrade is a key testbed for innovative divertor concepts, particularly the Super-X divertor. This design increases the path length for particles travelling from the plasma edge to the target plates, allowing the plasma to cool significantly before contact and reducing the incident heat flux. The UKAEA reports that the Super-X divertor alone has demonstrated the ability to reduce peak heat loads by a factor of 10. The successful integration of RMP control with this advanced divertor configuration provides a powerful, combined solution. These findings, based on experimental results from the facility, offer a promising pathway for designing more compact and resilient exhaust systems for future power plants. Source: UKAEA

The ability to actively control heat distribution is not just about component longevity; it directly impacts the economic viability and operational availability of a fusion power plant. A robust divertor solution that can withstand the harsh reactor environment for extended periods reduces the need for frequent and costly maintenance cycles. By validating a method to precisely manage where the plasma's heat is deposited, the UKAEA team has provided crucial data for the engineering design of DEMO and other commercial-scale fusion concepts. The next steps will involve further characterizing the performance of RMPs across different plasma scenarios and integrating the control system into routine high-power operations on MAST Upgrade. Source: UKAEA