Tokamak Energy developing laser for fusion power plant operations

14 Mar 2024

Laser-based interferometer under test in UK before installation in fusion machine “ST40”.

Tokamak’s ST40 system has been upgraded to improve its capabilities.

Tokamak Energy, based in Oxford, UK, is developing new laser measurement technology crucial for controlling extreme conditions inside future fusion power plants and delivering clean energy to the grid.

Tokamak Energy was founded in 2009 as a spin-off from the UK Atomic Energy Authority (UKAEA). Its US subsidiary, Tokamak Energy Inc, was established in 2019. The private fusion company has more than a decade’s experience developing the two technologies that offer the most efficient and commercially attractive route to fusion energy – the compact spherical tokamak; and high temperature superconducting (HTS) magnets.

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 in order to keep the hot 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 fusion machine ST40 later this year.

‘Measuring plasma density is key‘

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 move forward on our mission of delivering clean, secure and affordable fusion energy in the 2030s,” said Dr. Pyragius.

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. Importantly, this system also shows great promise in being 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, the threshold for commercial fusion. ST40 also achieved the highest triple product by a private company. Triple product is a widely recognised industry measure of plasma density, temperature and confinement, collectively a key measure of progress on the path to realising commercial fusion conditions.

After breaking the records in 2022, ST40 has been through a series of 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.