Oxford, UK – October 20, 2025 – Tokamak Energy, a leading private fusion energy company, has released new high-speed color footage offering unprecedented visual insights into plasma behavior within its ST40 spherical tokamak. The detailed imagery, captured at 16,000 frames per second, is providing researchers with a valuable tool to trace the movement and characteristics of different elements within the superheated plasma, advancing critical research for future fusion power plants.
This development marks a significant step in understanding and controlling the extreme conditions necessary for fusion, a process that promises a clean, virtually limitless energy source. The use of a high-speed color camera is enhancing diagnostic capabilities on the ST40, which previously achieved a plasma ion temperature of 100 million degrees Celsius in 2022, a critical threshold for commercial fusion.
Unpacking the Colorful Revelations of Plasma
The newly released imaging from the ST40 reveals distinct color variations that correspond to different substances and their states within the plasma. These visual cues complement existing spectroscopic data, offering a more intuitive understanding of complex plasma dynamics.
Deuterium Gas: The Pink Glow of Fusion Fuel
One of the most identifiable features in the footage is the bright pink glow emanating from injected deuterium gas. Deuterium, an isotope of hydrogen, is a primary fuel for fusion reactions. A pure hydrogen plasma, or its isotopes like deuterium or tritium, typically produces a light pink hue due to the emission of both red and blue light wavelengths.
Lithium’s Journey: From Crimson to Greenish-Yellow Streaks
A key focus of current experiments involves the introduction of lithium granules into the plasma using a newly installed Impurity Powder Dropper (IPD). As these sand-sized grains fall into the plasma:
- Crimson Red: Neutral lithium atoms, excited in the cooler outer regions of the plasma, emit a crimson-red light.
- Greenish-Yellow: As lithium penetrates deeper into the hotter, denser plasma, it loses an electron and becomes singly ionized lithium (Li⁺). This ionized lithium then emits a greenish-yellow light and begins to follow the confining magnetic field lines, appearing as distinct streaks tracing the magnetic fields around the tokamak.
These color changes allow researchers to visually track the path and behavior of lithium, providing crucial information about its interaction with the plasma and magnetic confinement.
The Significance for Fusion Research
The ability to visualize plasma behavior in such detail is a significant advancement for fusion energy research, particularly for understanding X-point radiator (XPR) regimes and material interactions.
Advancing X-Point Radiator (XPR) Regimes
This experiment is part of ongoing research into X-point radiator (XPR) regimes, an operating mode considered promising for future fusion power plants. XPR regimes aim to cool the plasma before it reaches the plasma-facing components (PFCs) of the tokamak. This cooling helps to reduce wear on these critical components without compromising the overall performance of the fusion reaction. The color imaging is proving to be a valuable diagnostic tool in these studies, as explained by physicist Laura Zhang.
Understanding Plasma-Material Interaction
The visual tracking of lithium within the plasma provides direct evidence of how introduced materials interact within the extreme environment of a tokamak. This understanding is vital as Tokamak Energy is also working on applying lithium coatings to all PFCs using an evaporation technique, building on pioneering work that has shown lithium PFCs can significantly improve plasma performance. The program also includes replacing carbon armor tiles with molybdenum, a more power-plant-relevant refractory metal, and adding new diagnostics to measure plasma with greater fidelity.
Tokamak Energy’s Broader Vision
Tokamak Energy, a spin-off from the UK Atomic Energy Authority (UKAEA) founded in 2009, is dedicated to commercializing clean fusion energy by the 2030s. The company focuses on two key technologies: compact spherical tokamaks, like the ST40, and high-temperature superconducting (HTS) magnets.
The ST40 is a high-field spherical tokamak that achieved 100 million-degree plasma temperature in 2022, a world-first for a privately funded spherical tokamak. This continued research on the ST40, supported by advanced diagnostics such as the high-speed color camera, is crucial for scaling up to energy-producing fusion devices and enhancing the understanding of plasma behavior.
