Fusion researchers spot strange, high-energy behavior in burning plasma

Mimicking the extreme reactions that take place inside the Sun, as is the aim of nuclear fusion researchers of all persuasions, is one thing. Having them generate heat to keep the reactions going and produce clean, limitless energy, would be the true holy grail. Researchers recently took an important step towards this goal with the achievement of a self-heating “burning plasma,” and now a closer inspection of that plasma has revealed strange, unexplained behavior of ions within it.

Scientists at the National Ignition Facility (NIF) have been pursuing nuclear fusion since 2009, using an array of 192 lasers to shoot high-energy pulses at a fuel capsule around the size of a ball bearing. This pellet of fuel is made up of deuterium and tritium, and obliterating it with sudden and intense heat causes the separate atoms to fuse into helium, releasing tremendous amounts of energy in the process.

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In an ideal world, fusion researchers would have these fusion reactions serve as the source of heat, doing away with the lasers and having these encounters power themselves to become a self-sustaining source of energy. In January this year, scientists at NIF published research in which they detailed important steps toward that dream, tweaking their technique to create a self-perpetuating “burning plasma.”

Although the burning plasma existed for mere nanoseconds, the research was a first for the field and an important advance in this branch of fusion research, known as inertial confinement fusion (ICF). New analysis of this burning plasma has now shown it behaves in an unexpected way, with the ions inside it shown to have higher energy than what the models had projected.

“This implies that the ions undergoing fusion have more energy than expected in the highest-performing shots, something that isn’t predicted – or able to be predicted – by the normal radiation hydrodynamics codes used to simulate ICF implosions,” said Alastair Moore, lead author of the new paper.

The scientists liken the unexpected, high-energy behavior of the ions to the Doppler effect, in the same way you might hear shifts in a police siren as the car approaches, passes by and then drives off into the distance. The team says more advanced simulations are needed to properly flesh out the processes at play, but doing so could provide key insights for the design of fusion facilities moving forward.

“Understanding the cause of this departure from hydrodynamic behavior could be important for achieving robust and reproducible ignition,” the team writes.

The research was published in the journal Nature Physics

Source: National Ignition Facility


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