Tokamak Energy has successfully replicated fusion power plant fields for the first time in its magnet demonstration system. The company’s Demo4 – a complete set of HTS magnets built in a tokamak configuration – achieved field strengths of 11.8 Tesla at -243 degrees Celsius in recent tests conducted at its headquarters outside Oxford, UK.
Strong magnetic fields are generated by passing large electrical currents through arrays of electromagnetic coils assembled in a cage-like formation. The magnets are wound with precision from HTS tapes using multi-layered metal conductors with a crucial internal coating of ‘rare earth barium copper oxide’ (REBCO) superconducting material. In a fusion power plant, each REBCO superconducting tape must operate within the complex, combined magnetic environment created by neighbouring coils – conditions that significantly influence its effective critical current and structural performance. These system-level interactions cannot be captured through individual magnet tests. Demo4 is a unique high field platform to generate and study fusion-relevant forces across a system coil set of 14 toroidal field magnets and two poloidal field magnets. Further testing to reach higher magnetic fields continues, with next results due in early 2026.
During the test Demo4 had seven million ampere turns of electrical current running through its centre column, demonstrating huge potential for power distribution as HTS can deliver around 200 times the current density of copper.
The company says the Demo4 device also demonstrates the potential of high temperature superconducting (HTS) technology across a range of spin-out applications, from power distribution for data centres, electric motors for zero emission flight, and fast, efficient magnetic levitation transport systems.
Warrick Matthews, Tokamak Energy CEO, said: “These results are a major victory for the race to deliver fusion and HTS as a disruptive new commercial technology. Demo4…validates one of the technical solutions for getting clean, limitless, safe and secure fusion energy on the grid.”
