Tokamak Energy developing laser system to measure plasma density

Based near Oxford, the company aims to commercialise fusion energy through the combined development of spherical tokamaks with high temperature superconducting (HTS) magnets and utilising the hydrogen fuel combination of deuterium-tritium.

Tokamaks are based around a torus (a doughnut-shaped vacuum chamber) in which gaseous hydrogen is subjected to extreme heat and pressure until it becomes plasma.

Plasma temperatures inside a tokamak reach over 100 million degrees Celsius. The hydrogen fuel must be closely and accurately measured by a specialist laser system to keep the burning plasma stable, hold density and maintain fusion conditions.

The new laser-based dispersion interferometer system is currently being tested at Tokamak Energy’s Oxford headquarters before being installed on its ST40 fusion machine later this year.

In a statement, Dr Tadas Pyragius, Tokamak Energy plasma physicist, said: “Measuring plasma density is key to our understanding and control of the fusion fuel and efficient future power plant operations. A laser beam fired through the plasma interacts with the electrons and tells us the density of the fuel, which is essential for sustained fusion conditions and delivering secure and reliable energy to the grid.

“The extreme conditions created by the fusion process mean we need to perfect the laser-based diagnostics technology now to drive forward on our mission of delivering clean, secure and affordable fusion energy in the 2030s.”

Tokamak Energy successfully commissioned a Thomson scattering laser diagnostic on ST40 in 2023 to provide detailed readings of plasma temperature and density at specific locations.

To supplement this, the new dispersion interferometer system will determine average density across the entire plasma. Tokamak Energy added that the system could be suitably robust and reliable to operate in future power plant environments.

ST40 is the first privately owned fusion machine to reach a plasma ion temperature of 100 million degrees Celsius, which is the threshold for commercial fusion. In another advance, ST40 also achieved the highest so-called triple product – an industry measure of plasma density, temperature and confinement - by a private company.

After breaking the records in 2022, ST40 has been through hardware upgrades to improve its capabilities, including new power supplies and diagnostic systems. Last year it focused on improving understanding and developing high-performance diverted plasma scenarios in a high field spherical tokamak. It will be back in operation later in 2024 following further upgrades and maintenance.