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Tokamak Energy achieves superconducting fusion magnet milestone

Published on 12 September 2023

Leading commercial fusion energy company Tokamak Energy has announced its superconducting fusion magnet system has passed significant milestone cryogenic tests, replicating forces of a fusion energy power plant.

Headquartered at Milton Park, this means Tokamak’s premises here is home to one of the largest extremes in temperature across the site – from its 100 million degrees Celsius fusion plasma to its -253 degrees Celsius cryogenic Demo4 testing.

In a major achievement for the company, engineers working on its ground-breaking Demo4 system at Milton Park have successfully validated electromagnetic current test results on the first of 14 toroidal field (TF) limbs in liquid nitrogen, at -200 degrees Celsius.

Demo4 will be a complete balanced set of magnets shaped in a tokamak configuration with an incredible 12 million amps of electricity running through its central column when fully assembled.

Dr Rod Bateman, Magnet Development Manager at Tokamak Energy, said: “These first set of extremely positive results are a major step forward for the Demo4 project, which will allow us to create substantial magnetic forces and test them in fusion power plant-relevant scenarios for the first time.

“A magnet system of this kind has never been built before so for the first toroidal field limb to perform as we expected under rigorous cryogenic electromagnetic current testing is a huge achievement. We now move forward to the next stage with great confidence in our manufacturing process on the path to delivering clean, secure and affordable fusion power in the 2030s.”

Demo4 will consist of 44 individual magnetic coils using 38 kilometres of 12mm wide high temperature superconducting (HTS) tape, which carries currents with zero electrical resistance and requires five times less cooling power than traditional superconducting materials. A TF limb consists of two coils being joined, resin moulded, and embedded into a structural steel ‘clam shell’.

The system will operate in a vacuum at an extremely low temperature of -253 degrees Celsius – 20 degrees above absolute zero – achieved by 10 closed-cycle cryocoolers. It will also demonstrate the potential of HTS magnets for other important applications.

Strong magnetic fields are generated by passing large electrical currents through arrays of electromagnet coils that will surround the plasma in future power plants. The magnets were wound with precision from state-of-the-art HTS tapes, which are multi-layered conductors with a crucial internal coating of ‘rare earth barium copper oxide’ (REBCO) superconducting material.

Final Demo4 assembly and testing at Tokamak Energy’s Milton Park headquarters, will take place in 2024.

For more information on Tokamak Energy and its work, please visit:

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