Australasian Science: Australia's authority on science since 1938

Fusion Failure Fixed

Scientists have worked out why the beams they use to heat hydrogen gas to a plasma ten times hotter than the Sun sometimes destabilise their fusion experiments before energy is generated.

The solution, published in Physical Review Letters (www.tinyurl.com/hp6zn7d), used a new theory that treated plasma as a fluid rather than individual atoms.

Nuclear fusion of hydrogen into helium is the process that powers stars. It promises a large-scale energy source based on fuel extracted from water, and doesn’t create the long-term waste that uranium-based nuclear fission does.

The fusion experiments heat hydrogen gas until it becomes a plasma, and then use strong magnetic fields to hold it in place until fusion reactions occur. However, plasma this hot is extremely turbulent and can behave in surprising ways that baffle scientists, at times becoming unstable and dissipating before any fusion reactions can take place.

“There was a strange wave mode which bounced the heating beams out of the experiment,” said lead author Zhisong Qu, a PhD student at The Australian National University.

Qu developed a simpler theory for plasma behaviour based on fluid flow, and was able to explain an unstable wave mode that had been observed in the United States’ largest fusion experiment, DIII-D.

Collaborator Dr Michael Fitzgerald, from the Culham Centre for Fusion Energy in the UK, said the new explanation made much more sense than previous “brute force” theories that tried to treat plasma as individual atoms. “When we looked at the plasma as a fluid we got the same answer, but everything made perfect sense,” Fitzgerald said. “We could start using our intuition again in explaining what we saw, which is very powerful.”

Leader of the research group, A/Prof Matthew Hole of ANU, said the theory’s success with the DIII-D wave puzzle would “open the door to understanding a whole lot more about fusion plasmas, and contribute to the development of a long-term energy solution for the planet.”