In the 1990 film The Hunt for Red October, a Soviet naval captain played by Sean Connery pilots a submarine powered by a “magnetohydrodynamic drive” that is undetectable to military sonar.
A quarter of a century later, UK start-up Tokamak Energy is supporting a US Defense Advanced Research Projects Agency programme to make silent marine propulsion a reality.
The collaboration with Darpa is one of several ways the nuclear fusion company is seeking to monetise a decade of work on high temperature superconductor magnets, which it argues can transform sectors from public transport to medical imaging.
“What we want to do here is usher in the HTS era,” said Liam Brennan, director of TE Magnetics, which Tokamak Energy will officially launch next week. “We want to get those magnets out there and get them operating.”
Spun-out of the UK Atomic Energy Authority in 2009, Tokamak Energy’s principal business is nuclear fusion, where the Oxfordshire-based company is vying with about 40 others worldwide to be the first to develop a power plant capable of producing commercially viable clean power by fusing hydrogen isotopes.
The prospect of recreating the reaction that powers the sun has tantalised scientists for decades. The carbon-free reaction creates no long-lived radioactive waste, the isotopes can be sourced in large quantities, and a small cup of the fuel has the potential to power a house for hundreds of years.
But after 60 years of experiments no group has been able to perfect the technology and there is no guarantee the dream of fusion power plants will be realised.
The most common approach to fusion uses magnets to suspend a plasma of two isotopes — normally deuterium and tritium — in a device called a tokamak. The isotopes are then heated to extreme temperatures 10 times hotter than the centre of the sun so the nuclei fuse, producing helium and energy.
The first generation of magnets used in experimental tokamaks such as JET in Oxfordshire, which began operations in 1983, were made of copper. More recent facilities, such as China’s EAST, which produced its first plasma in 2006, use so-called low temperature superconductor magnets.
Tokamak Energy will use its specially designed HTS magnets wound from groundbreaking tape that can generate a much stronger magnetic field, at higher temperatures, than LTS magnets. The crucial component in the copper-covered tape is a layer — about the width of a human hair — of superconducting material rare earth barium copper oxide.
Whereas LTS materials have to be cooled using expensive liquid helium to temperatures close to absolute zero (minus 273C), rebco tape exhibits superconducting properties at roughly minus 200C, making HTS-based systems potentially cheaper and more powerful.
Tokamak Energy in 2019 built and tested the world’s highest-field HTS magnet, achieving a record 24 tesla field at a temperature of minus 253C. The magnets in the JET device, which was decommissioned this year, could only generate magnetic fields of up to 4 tesla.
“We’ve shown with our magnets that we can make them very reliable, stable and consistent, and that’s the tipping point,” said Brennan. “This couldn’t be done seven years ago.”
Tokamak Energy’s advances in magnet technology are vital to its fusion plans. Whereas most existing tokamaks are doughnut shaped, it plans to build a more compact spherical one, which will require the machine’s magnets to perform as efficiently as possible.
It aims to build a pilot plant capable of delivering electricity into the grid in the early 2030s. The UK government’s next fusion device, STEP, will use a similar design.
To test the science and engineering in its magnets, Tokamak Energy has built a demonstration device at its facility outside Oxford. When completed this year it will stand 3.2 metres tall and include 44 magnetic coils of HTS tape arranged in a spherical formation around a central core. The machine will replicate the forces required in a fusion power plant, producing a magnetic field of 18 tesla, nearly a million times stronger than the Earth’s magnetic field.
However, the potential applications of HTS magnets extend beyond fusion. The ability to operate without the need for costly liquid-helium cooling and a high tolerance to vibration makes HTS magnets ideal for use in MRI scanners in hospitals and other scientific imaging equipment that currently use LTS materials, Brennan said. He said other applications of the superconducting qualities of HTS could also include shrinking the size of electric motors for trains.
The Darpa programme on maritime propulsion requires HTS magnets, he said, because it is seeking to build magnetohydrodynamic drives that produce magnetic fields of 20 tesla.
The only such drive tested to date was developed by Japan’s Mitsubishi in the 1990s and then abandoned. The drive generated a magnetic field of approximately 4 tesla, which successfully propelled a 30-metre boat but only at speeds of 6.6 knots (about 12 km/h).
By selling its magnet expertise to other fusion companies and industries, Tokamak Energy says it can ease its future funding requirements. Private sector fusion companies have raised about $7bn in investment to date but fundraising is challenging as long as revenues from commercial fusion power remain at least a decade away.
Tokamak Energy, which employees about 250 people, is in the middle of another funding round having previously raised $250mn from private investors and government grants. At least $50mn of that has been spent on magnet development.
“It’s a very difficult investment story because your typical venture capital investors are looking for a return in a defined period of time, and the magnets business helps us there because we can actually point to a return,” said Christian Lowis, the company’s general counsel.
The company has already signed HTS-related contracts with several customers and estimates TE Magnetics could generate £8mn in annual revenues next year and £300mn a year by the end of the decade.
“Key to our model is owning the design of the magnets,” Lowis said. “Whether we manufacture the magnets, subcontract the manufacture to somebody else, sublicence the IP to somebody else or even sublicence them to another fusion company for them to manufacture themselves, they’re all potential options.”
Graphics by Ian Bott
