The UK Atomic Energy Authority (UKAEA) has completed its fifth series of experiments on its MAST Upgrade fusion machine, achieving the highest plasma pressure to date. These experiments, which ran through 2025 and 2026, produced over 1,100 fusion plasmas at UKAEA's Culham Campus in Oxfordshire.
The team overcame plasma instability issues, which are considered essential prerequisites for commercial fusion power. They pioneered a novel technique that uses measurements of light to detect and control minute plasma imbalances in real-time.
A central challenge was suppressing "Edge Localised Modes" (ELMs), sudden bursts at the plasma's outer edge that can cause energy loss and damage. The team adopted techniques such as the Quasi-Continuous Exhaust mode (QCE-mode) and Resonant Magnetic Perturbations (RMP) to reduce plasma pressure at the edge and maintain stability. They also accessed stable operating regimes known as Quiescent H-mode (QH-mode) and I-mode, which improve energy confinement while mitigating large ELMs.
The experiments also explored injecting small amounts of nitrogen into the plasma edge to dissipate excess heat as light, reducing wear on inner surfaces. This impurity-assisted method is expected to be essential for future fusion power plants.