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UK-based Tokamak Energy is developing new laser measurement technology to control extreme conditions inside future fusion power. Plasma temperatures inside a tokamak reach over 100m degrees Celsius. The hydrogen fuel must be closely and accurately measured by a specialist laser system 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. Tokamak Energy commissioned a Thomson scattering laser diagnostic on ST40 last year to provide detailed readings of plasma temperature and density at specific locations.

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.”

He added: “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.”

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 100m 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.

Tokamak Energy in February 2023 announced plans to build a prototype spherical tokamak, the ST80-HTS, at the UK Atomic Energy Authority's Culham Campus, near Oxford, England, by 2026 "to demonstrate the full potential of high temperature superconducting magnets". This will underpin the design of its planned fusion pilot plant, ST-E1 intended to demonstrate the capability to deliver electricity - producing up to 200 MWe in the early 2030s. The next step would be construction of 500 MW commercial fusion plants "in the mid-2030s".

After breaking 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.

The company was founded in 2009 as a spin-off from UK Atomic Energy Authority and currently employs a growing team of over 250 people. It has 70 families of patent applications and has raised $250m, comprising $200m from private investors and $50m from the UK and US governments.

Image: Tokamak Energy is developing a new laser system that will be used to measure plasma inside future fusion power plants (courtesy of Tokamak Energy)

Date: Thursday, 21 March 2024
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