Tokamak completes set of HTS magnets

Monday, 6 February 2023

"Creating clean, sustainable fusion energy requires strong magnetic fields to confine and control the extremely hot, positively-charged hydrogen fuel, which becomes a plasma several times hotter than the Sun," Tokamak said.

The Oxfordshire-based company's new Demo4 facility will consist of 44 individual magnetic coils recently manufactured using 38 kilometres of ground-breaking HTS tape, which carries currents with zero electrical resistance and requires five times less cooling power than traditional superconducting materials.

The HTS tapes are multi-layered conductors made mostly of strong and conductive metals, but with a crucial internal coating of 'rare earth barium copper oxide' (REBCO) superconducting material. The tapes are typically 12mm wide and less than 0.1 mm thick, with REBCO deposited as a thin coating. When wound into coils, HTS tapes can generate much higher magnetic fields than conventional superconducting magnets, while taking up far less space and requiring far less cooling power.

Comprising 14 toroidal field (TF) limbs and a pair of poloidal field coil stacks to form a cage-shaped structure, Demo4 will have a magnetic field strength of over 18 Tesla, nearly a million times stronger than the Earth's magnetic field. It will need be tested at an extremely low temperature of minus 253°C.

A cutaway of Demo 4 (Image: Tokamak Energy)

Demo4 will demonstrate the interaction of all the coils and will show how to control and protect a balanced set of HTS coils in a tokamak configuration. It will also create substantial magnetic forces and test them in fusion-relevant scenarios.

Full assembly of Demo4 at Tokamak's headquarters in Milton Park, near Oxford, will be completed later year and testing will extend into 2024, informing designs and operational scenarios for its advanced prototype, ST80-HTS, and subsequent fusion power plant, ST-E1.

"Tokamak Energy has been a pioneer in recognising the opportunity to apply and develop high temperature superconducting technology for fusion energy," said Tokamak Energy CEO Chris Kelsall. "The learnings from Demo4 will be a key catalyst for delivering the global deployment of compact, low-cost spherical tokamak power plants."

"This is a huge, visible moment that we're really excited about," added Rod Bateman, HTS Magnet Development Manager at Tokamak. "Our magnets enable the construction and operations of spherical tokamaks, and so are a game changer for getting clean, limitless fusion energy on the grid faster.

"Demo4 will allow us to create substantial magnetic forces and test them in fusion power plant-relevant scenarios. Importantly, it will substantially progress the technology readiness level of HTS magnets as a key part of our mission to demonstrate grid-ready fusion in the early 2030s."

Tokamak Energy's roadmap is for commercial fusion power plants deployed in the mid-2030s. To get there the plan is for completion of ST80-HTS in 2026 "to demonstrate the full potential of high temperature superconducting magnets" and to inform the design of its fusion pilot plant, ST-E1, which is slated to demonstrate the capability to deliver electricity - producing up to 200 MW of net electrical power - in the early 2030s.

In January, Tokamak said it had signed an agreement with Japan's Furukawa Electric to supply "several hundred kilometres" of HTS tape for its ST80-HTS prototype fusion device. The HTS tape has been developed and is being supplied by Furukawa, with the production of the tape under way at the group's SuperPower Inc's site in New York in the USA.