Fusion Diary: Inside Britain's Race To Fusion

Although this radioactivity poses nothing remotely comparable to the long-term hazards associated with nuclear fission waste, maintenance of the reactor will nevertheless have to be done by human-operated remote control or by robotic systems.

Culham has a major facility named RACE (Remote Applications in Challenging Environments), devoted to developing sophisticated robotic systems of the required sort. Needless to say, these systems have many applications beyond fusion.

In a fusion-producing tokamak like JET the approximately 100-million-degree hot plasma is confined and suspended within a toroidal vacuum chamber by the magnetic field resulting from a combination of intense internal currents and powerful external coils.

Remarkably, the UK has chosen for its national program a special design that differs in essential ways from conventional tokamaks such as JET. It is called the spherical tokamak.

Spherical tokamaks were a central theme during my visit. In place of the broad, massive solenoid running through the“hole of the doughnut” in a classical tokamak such as JET, a spherical tokamak has only a narrow central post, bringing the plasma much closer up to the vertical axis of the reactor.

As it turns out, the difference in shape has a profound effect on the behavior of the plasma in the reactor, as well as on the design and operating parameters of the magnetic coils and other reactor components. As I shall explain in some depth in a later article in this series, STs have unique advantages for use in future fusion power plants.

In a shrewd and daring decision, the UK has opted for the spherical tokamak design for its projected demonstration fusion power plant. This decision breaks with the international consensus in favor of the conventional tokamak design, embodied in the giant International Thermonuclear Experimental Reactor under construction in France.

During my stay I was able to visit two major spherical tokamak devices in operation, one at the Culham Centre for Fusion Energy and the other at the private company Tokamak Energy.

After the visit to JET I interviewed at length Paul Methven, Director of the UK's STEP program . STEP, which stands for“Spherical Tokamak for Energy Production,” aims not only to build a demonstration electricity-producing fusion reactor but also to create a national fusion industry at the same time. I feel pretty sure that nothing like STEP would have come about if the UK had remained in the European Union.

Asia Times will be publishing the full Methven interview as part of this article series. The interview sheds light on one of the key challenges of realizing fusion power plants, which has so far drawn little public attention.

At this point there is no reasonable doubt concerning the feasibility of generating large amounts of net energy by fusion reactors of the tokamak type. The real challenge is to design and build systems that can operate for long periods at an acceptable cost, and finally to turn them into commercially viable sources of electricity.

In our discussion, Paul Methven drew an analogy between STEP and the Apollo program of the 1960s – an effort of vast complexity that culminated in the first landing of astronauts on the Moon.

In some respects the problem resembles a jigsaw puzzle. A large number of interconnected technical and technological problems must be resolved, in such a way that the resulting components and subsystems fit together in a single functioning whole. Not least of all is the challenge of organizing and managing this vast endeavor, which will eventually involve thousands of scientists and engineers working in dozens of national laboratories and private companies.

Culham was the birthplace of the first spherical tokamak in the world – the Small Tight Aspect Ratio Tokamak (START). I shall go into the ST and its adventurous past in detail later in this series.

The second-generation device, called the Mega Ampere Spherical Tokamak (MAST), provided decisive proof of the superiorities of the ST design. The device I visited is called MAST-U, an upgraded version of the MAST.

This upgraded version is devoted mainly to finding the optimum design for the so-called divertors, which are critical components of any power-generating tokamak reactor. Divertors basically“clean” impurities and products of the fusion reactions from the plasma, while absorbing about 20% of the energy output. Readers can find a brief introduction to this concept in an earlier Asia Times article on China's EAST reactor.

One of MAST-U's most notable features is the so-called Super-X divertor – a major breakthrough in divertor design which, among other things, promises to greatly improve the economics of future tokamak power plants.

On the tour, I was shown the MAST-U control room and had the opportunity to discuss ongoing work on the Super-X diverter in some detail with a specialist at the facility.

On the next day, I visited the facilities of First Light Fusion , a private company working with a completely different approach to fusion. First Light's technology is an innovative form of so-called inertial confinement fusion, in which the energy is released in the form of micro-explosions of tiny pellets filled with fusion fuel.

Laser fusion is the most well-known example. In place of laser pulses, however, First Light generates fusion reactions by hitting the fuel with a small metal projectile accelerated to enormous velocities.

At the First Light facility, I was shown two different devices used for this purpose.

One, affectionately called the is a type of two-stage cannon, which achieves projectile velocities of 7 kilometers per second – over 20 times the speed of sound. I examined the target chamber where the projectile strikes the fusion target, flanked with neutron counters.

The second accelerator device built by First Light propels the projectile by a gigantic pulse of electricity, projected to reach velocities of 20 km per second (Mach 60). This system, which fills an entire hall, is the largest pulsed power facility in Europe. A rather impressive piece of equipment!

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The“secret” of First Light, however, does not lie in the accelerator systems, but in a patented so-called“amplifier” in which the fuel capsule is embedded. The“amplifier” serves to focus the shock waves, generated by the impact of the projectile, onto the target. First Light has already produced bursts of neutrons from fusion reactions.

, told me about the strategy adopted by First Light Fusion. He explained how this approach to fusion, while highly innovative, is based on well-established physical principles, experimental results and computer modeling.

Recognizing the promise of this method, the UK Atomic Energy Agency has signed an agreement with First Light for the design and construction of a new facility at Culham to house the company's next stage-device, designed to demonstrate net energy release by fusion. This is part of the UKAEA's effort to create a cluster of private fusion companies on the Culham campus.

Finally, I visited the Tokamak Energy company , which has pioneered the design, construction and operation of advanced spherical tokamaks since 2009.

Tokamak Fusion's ST-40 reactor. Photo: Tokamak Fusion

In a discussion, Tokamak Energy's executive vice chairman David Kingham described the company's strategy and roadmap, which aims at putting a first electricity-producing unit online by the mid-2030s.

He also recounted the story of how the spherical tokamak, initially rejected as a crazy idea, came to be adopted by the UK as the most promising design for a future fusion power plant.

Chief Technical Advisor Paul Thomas with the author in the ST-40 control room. Photo courtesy of author

I was shown the control room of their current device, the ST-40. Last year the ST-40 achieved a record temperature for a spherical tokamak of 100 million degrees.

Earlier this year it was announced that Tokamak Energy's next-step spherical tokamak, ST80-HTS, will be built inside the CCFE campus, as part of the growing cluster of fusion companies I mentioned above.

Decisive for Tokamak Energy's strategy is to employ coils made of high-temperature superconductors (HTS) to realize extremely compact, high-field spherical tokamaks.

Tokamak Energy has a specialized facility devoted to developing HTS coils able to operate reliably in the extreme environment of a fusion-producing reactor. A young scientist there proudly showed me some of the HTS coils he has been building and testing.

All in all, the most inspiring thing about my trip was to witness the extraordinary enthusiasm and inventiveness of brilliant young scientists and engineers, who have devoted themselves to realizing fusion as a boundless energy source for humanity's future.

NEXT: Visiting the world's largest fusion reactor

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.

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