Physicists take big step to solving nuclear fusion’s biggest ‘leaky’ problem

25 Feb 2020

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Physicists working to make nuclear fusion a reality have overcome one of the biggest hurdles in making a reactor less leaky.

Nuclear fusion remains the dream for many physicists, as harnessing the power of the sun within a reactor could usher in an age of near-limitless, cheap and clean energy. However, one of the biggest hurdles to overcome is in a reactor’s tendency to ‘leak’ the heat and performance of the plasma that fuels key reactions.

Now, researchers from the US Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) and the Max Planck Institute in Germany may have found a key step to overcoming this problem.

The discovery was made using the largest and most advanced stellarator ever built, the Wendelstein 7-X (W7-X). It is designed to improve the performance and stability of the plasma – the hot, charged state of matter made from free electrons and ions, which makes up 99pc of the visible universe.

Recent research wanted to find whether the design of W7-X could temper the leakage of heat and particles from the core of the plasma, which has long slowed the advancement of stellarators.

“That is one of the most important questions in the development of stellarator fusion devices,” said PPPL physicist Novimir Pablant, lead author of a paper published to the journal Nuclear Fusion.

This leakage – referred to as ‘transport’ – is a common problem for stellarators and more widely used fusion devices called tokamaks, which have traditionally better coped with the problem.

‘A rare moments in a scientist’s life’

The most common causes of transport include turbulence – represented by the unruly swirling and eddies of plasma – or particles orbiting magnetic fields colliding and knocking them out of their orbits, resulting in ‘neoclassical transport’.

The designers of W7-X sought to overcome these issues by carefully shaping the complex, 3D magnetic coils that create the confining magnetic field. Pablant and his fellow researchers compared their work with measurements of plasma behaviour in previous W7-X experiments and testing, showing it brings significant benefits.

“This research validates predictions for how well the optimised design of the W7-X reduces neoclassical transport,” Pablant said, adding that “unoptimised stellarators have done very poorly” in controlling the problem.

Andreas Dinklage, a Max Planck physicist, said the stellarators’ ability to better hold plasma came “much earlier than expected”.

“I recall my excitement seeing [Pablant’s] raw data in the control room right after the shot,” he added.

“I immediately realised it was one of the rare moments in a scientist’s life when the evidence you measure shows that you’re following the right path. But even now there’s still a long way to go.”

Colm Gorey was a senior journalist with Silicon Republic