Supermagnets changing the rules of nuclear fusion

Supermagnets changing the rules of nuclear fusion

This is the seventh installment in Asia Times Science Editor Jonathan Tennenbaum’s series “Fusion Diary.” Read part 1part 2part 3part 4Part 5 and Part 6.

During my August visit to nuclear fusion facilities in the UK, I spent an afternoon at Tokamak Energy Ltd, one of the world’s leading private fusion companies. Tokamak Energy’s basic strategy is to apply the technology of high-temperature superconductors to build compact spherical tokamak reactors with super-intense magnetic fields, capable of achieving fusion conditions with high efficiency and at low cost.

Tokamak Energy is the only private fusion company that has more than 10 years’ experience of designing, building and operating its own tokamak devices. The company is pursuing an ambitious timeline, aiming to build a prototype electricity-producing fusion plant that would go onto the grid in the 2030s. 

Tokamak Energy has so far attracted over US$200 million in private investments, and possesses a substantial amount of intellectual property, among other things through its ground-breaking innovations in the area of high-temperature superconducting magnets. 

In contrast to many private fusion companies, Tokamak Energy is fully integrated into international fusion research, regularly publishing its results in peer-referred papers and working in partnership with institutions such as the Princeton Plasma Physics Laboratory, Oak Ridge National Laboratory, University of Illinois, CERN in Geneva and others. Tokamak Energy’s UA subsidiary was selected for an award as part of the US Milestone-Based Fusion Development Program.

Spherical tokamaks built and operated by Tokamak Energy  Left: ST25  Right: ST40    Photos: Tokamak Energy

Last year the company’s ST40 tokamak achieved a record temperature of over 100 million degrees Celsius – the highest temperature reached in a privately owned spherical tokamak reactor so far and a threshold for commercial fusion. ST40 operates with magnetic fields that are 3-5 times more intense than those of other spherical tokamak devices, such as the MAST-U or the USA’s “National Spherical Torus Experiment” (NSTX).

In addition to the temperature record, experiments on ST40 since 2018 have provided a wealth of data underlining the feasibility of achieving practical fusion power with this type of reactor. They support the UK government’s decision to place its chief bets on the spherical tokamak – rather than the conventional doughnut-shaped design adopted by other nations – in the race to fusion.

Left: Hot plasma in the vacuum chamber of Tokamak Energy’s ST40 reactor  Right: Tokamak Energy Chief Technical Advisor Paul Thomas, left, with the author in the ST40 control room.  Photos: Tokamak Energy

ST40 also validated a novel method of heating the plasma, called “merging compression.” Using a special set of magnetic coils, two rings of plasma are merged together, causing an event known as “magnetic reconnection” in which magnetic energy, stored in the plasma rings, is converted into heat.

YouTube video

Source: YouTube

Merging compression was used in last year’s experiments demonstrating record 100 million-degree temperatures.

While ST40 uses conventional copper coils, Tokamak Energy has already successfully employed high-temperature superconducting (HTS) coils in a smaller experimental device, the ST25. The next step after ST40 is larger device, christened STX, which will use 100% HTS coils and operate at much higher magnetic fields.

This device, scheduled for build completion in the late 2020s, is intended to demonstrate multiple advanced technologies required for fusion energy and inform the design of a fusion pilot plant. The plan is for the fusion pilot plant to demonstrate the capability of delivering electricity into the grid in the 2030s, paving the way for globally deployable 500-megawatt commercial plants.

A leader in high-temperature superconducting magnet technology

A particular focus of Tokamak Energy’s activity is the development of “super-magnets” employing high-temperature superconductors (HTS). The company is a world leader in this area. HTS coils capable of producing ultra-intense magnetic fields are key to the company’s strategy for achieving fusion, while having countless applications in other areas.

In my next article, I shall describe some of Tokamak Energy’s ground-breaking innovations in the area of HTS magnets.

Earlier this year Tokamak Energy entered into an agreement with the giant US firm General Atomics to collaborate on HTS technology for fusion energy and other industrial applications. GA is a leading high-technology company active in the fields of fission and fusion energy, defense and aerospace. The two companies announced that their collaboration “will leverage GA’s world-leading capabilities for manufacturing large-scale magnet systems and Tokamak Energy’s pioneering expertise in HTS magnet technologies.”

How Tokamak Energy began

David Kingham. Photo: Tokamak Energy

During my visit, I had the opportunity to talk with Tokamak Energy cofounder David Kingham about the company’s history and its future perspectives.

Jonathan Tennenbaum: Could you tell me a bit about the background of your company, and how you came to be building spherical tokamaks?

David Kingham: Back in the late 1970s, early ’80s, a guy called Martin Peng was working on the theory of spherical tokamaks. That work was picked up by Alan Sykes at Culham in the 1980s and they could see theoretically the plasma physics was going to get better. But somebody had to build one of these without knowing what was going to come out.

Alan Sykes basically badgered the director of Culham to build one, and he wouldn’t shut up about it. He said, “Let me build one.”

“There’s no budget.”

Alan Sykes. Photo: Tokamak Energy

“I don’t need a budget. just let me build it.”

So eventually the director gave way and said, “Okay. We’re not going to announce it in any budgets. You can borrow some stuff from some old tokamak and see what you can do.” So he cobbled this device together. He found a big enough vacuum vessel and the device is now known as START.

What it did was show very good plasma confinement and demonstrate high beta. People got pretty excited in the late 90s about its performance. My cofounder Mikhail Gryaznevich had joined START as one of the key scientists. He was behind this demonstration of high beta and high performance in START.

Then the UK government said, Oh, that’s interesting. That could be our next device. The spherical tokamak seemed to be a better way to go and UKAEA described it as probably the best option for the long term for fusion power. That was known and well-accepted in 2000.

UKAEA was running JET at the time, and JET had achieved 16 MW of fusion power.  At the same time, the people at the Princeton Plasma Physics Laboratory that ran TFTR (the Tokamak Fusion Test Reactor) successfully and got to 10 MW of fusion power also realized the spherical tokamak would be the way forward for them. So two devices were then built. MAST in the UK, at Culham, and NSTX in Princeton, both during the early 2000s. Both produced really exciting results, again validating the physics of the spherical tokamak.

Both were upgraded rather slowly from about 2012 onwards. Then we came on the scene and decided we would build ST40. We’d take the knowledge from NSTX and MAST. What we wanted to do was to go smaller and double or more the magnetic field. That’s our basic thesis. Go for a higher magnetic field. Then you can have a more compact device and you can sort out all the other engineering challenges by collaboration or just trial and error. 

In 2009 we formed the company, myself and Mikhail Gryaznevich, who’s now the chief scientist. The rationale was: The physics of the spherical tokamak is so good, it’s worth solving the very difficult engineering challenges.

Early on, we were looking at high-temperature superconductors, but it wasn’t really until 2011 that we did our first serious experiments with high-temperature superconductors. We did that by borrowing a tokamak in Prague and asking them nicely if we could replace their poloidal field coils with high-temperature superconducting magnets. So we did that and it worked. And we found the material was relatively easy to use and quite robust.

That set us on a pathway – spherical tokamak plus high-temperature superconducting magnets. The technologies match because you have a very narrow center column in the device. So you want a high-temperature superconductor, you want that very high current density. That gave us a solid foundation for the business from which we could build more intellectual property, and attract private investment.

Moving on, we attracted more and more private investment. Starting at a million pounds or less, the investment got up towards 10 million. In total, we’ve raised about 150 million pounds so far.

We have had support from the UK and US governments. The US Department of Energy supported research on ST40 and the UK government gave us significant grants and R&D subsidies. Princeton really got behind ST40. They’ve been really helpful on the physics, the data interpretation, experimental campaign advice and so forth.

We started to scale up. We always wanted to build prototypes and demonstrate performance rather than do too much theoretically or in subsystems. So we built one tokamak out of copper at small scale, and one using high-temperature superconducting magnets, but at a very low field, and that worked.

Then we decided to scale up quickly: to develop the ST40 with copper magnets, and in parallel, high-temperature superconducting magnets. So that’s where we are at the moment, planning our next device.

David Kingham (at right) with Member of Parliament David Johnston, in the ST40 control room. Photo: Tokamak Energy

JT: So what is your strategy moving forward?

DK: Fusion can’t be delivered by private companies or governments alone. The science horsepower of national laboratories with the speed and agility of a private company working together is very powerful. The US Department of Energy has set the target of a fusion pilot plant on grid within 10 years, and we have recently been awarded a grant as part of that process.

We like the time scale and ambition of that program.

JT: What would your role be in STEP?

DK: It’s also a great endorsement of our approach and technology that the UK’s fusion prototype plant [STEP] will be a spherical tokamak with HTS magnets. We are extremely excited about the UK’s investment in STEP and believe we can bring real value to the program with our extensive knowledge of spherical tokamak design and operation, along with our HTS magnet technology.

JT: In the meantime, I understand that you are planning to build another spherical tokamak.

DK: We would like to build some form of intermediate device that is before a pilot plant, say on a three- or four-year timeline from here, to de-risk technology. But that is essentially an option in our business plan rather than an essential part of it.

The overall business plan now is really to build up intellectual property and to become an IP provider to various consortia who will develop fusion energy. We’re pushing for this relatively capital-light, IP-intensive business model.

Warren East has recently joined our board. He was previously chief executive of Rolls-Royce. Before that, he was chief executive of ARM, which is just about to float at a $70 billion valuation. It’s a fabless semiconductor company based out of Cambridge, and it designs chips for everybody. It has protected its intellectual property around the high-performance chips.

So this is the business model that we’re aiming for: to have control of the greatest ownership of the highest-value components of future fusion reactor control systems, magnets, some novel materials, and some design capabilities.

Next: The magnet wizards

Jonathan Tennenbaum, PhD (mathematics), is a former editor of FUSION magazine and has written on a wide variety of topics in science and technology, including several books on nuclear energy.