Compact tokamaks: the approach to bring fusion energy within reach

31 May 2016

Fusion reactor development could proceed much more rapidly by scaling down the size of reactors being developed, potentially helping the first compact fusion pilot plants to be ready to produce electricity for the first time within the next decade, writes David Kingham.

Nuclear fusion is the creative process of the universe. All matter, besides hydrogen and a smattering of helium, was created in the fusion furnaces within stars as small atomic nuclei joined together to make larger ones. This reaction releases huge amounts of energy - about ten million times as much by weight as the chemical reaction of fossils fuels.

The established principle for such a reaction on Earth is to combine deuterium and tritium to make helium and a neutron. The neutron is not confined by the magnetic field of a fusion reactor and so flies out of the vessel and is captured to generate electricity.

But we can't just put a star in an ordinary box. The walls would get hot and the fusion fuel would get cold and stop fusing. The hot plasma must be isolated from the walls of the reactor. Charged particles are affected by magnetic fields, so this feat can be performed using magnets; the most advanced machine used for this purpose is the 'tokamak'. Tokamak is a Russian acronym that stands for toroidal chamber magnetic coils.

The best-performing tokamak in the world is JET, producing 16 MW of fusion power with 24 MW input in 1997 - i.e. 65% as much energy out as was put in. It holds the world record for total fusion power produced and for getting closest to breakeven. To reach this point, fusion research followed a Moore's law-like path. The temperature, density and energy confinement time, which indicates fusion performance, was increasing at a faster and faster rate up until the JET experiments.

But since then it seems that progress has stalled. There have still been experiments built and much learned, but progress towards energy breakeven has slowed. We still haven't actually reached energy breakeven almost 20 years after we nearly got there.

Traditional designs have moved to larger dimensions, culminating in the ITER experiment currently under construction in the south of France. This will be over 30m tall and weigh about 23,000 tonnes. The demonstration reactor that follows, dubbed DEMO, will likely be slightly bigger again. When ITER was being designed in the 1990s, it was believed that the only feasible way to increase fusion power was to increase machine size. But the size and complexity of ITER has led to very slow progress in the fusion program, with first fusion set for the mid 2020s. Tired of waiting so long and recognising the inherent difficulties of such a big project, some have been questioning the possibility of a smaller way to fusion.

Tokamak Energy is leading this movement. To date the company has published three papers showing size is not an important factor in fusion reactors and proving that a compact reactor can produce high power. This turns the pursuit of fusion into a series of engineering challenges. The Tokamak Energy plan will overcome these challenges, such as the development of magnets made from high temperature superconductors, delivering a fusion power gain within five years, first electricity within ten years and a 100 MWe power plant within 15 years.

All this is possible thanks to a new climate of private funding reaching into areas that were previously the domain of governments: ventures like Virgin Galactic and SpaceX; or The Breakthrough Energy Coalition, led by Bill Gates and Mark Zuckerberg, an investment fund for new energy technologies emerging from scientific research. Lord Rees of Ludlow, past President of the Royal Society, said in 2015, "the private sector now has greater appetite for risk in scientific projects than Western governments."

By breaking down the challenges into distinct goals, money can be raised privately to achieve each step, with success enabling more to be raised to tackle the next. The US is leading the way in terms of financial investment in private fusion, with a number of firms receiving around $100 million in investment to further numerous different styles of devices and processes. Tokamak Energy is determined that the UK should not be left behind in this race.

There is latent public enthusiasm; many people recognise that harnessing fusion energy is an important challenge that we have a duty to tackle. This new climate brings hope for a fusion future. While some hold the view that fusion will forever be 30 years beyond the horizon, we are working on the technology that is bringing us closer to fusion than ever before. The UK has led the world in developing fusion, creating the world-leading fusion device, JET. Tokamak Energy is making the UK the country that continues to drive fusion forward.

David Kingham

Comments? Please send them to editor@world-nuclear-news.org

Dr David Kingham is chief executive of Tokamak Energy, a private company that grew out from the UK's Culham Laboratory and is working to develop compact fusion power.

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