Research Stories: How a theory of nuclear fusion turbulence caused turbulence of another kind

The Source
By: Guest contributor, Tue Jan 24 2023

Author: Guest contributor

After submitting a high-profile paper in grad school, Josefine Proll endured a period of stress when a new post-doc pointed out an error in her calculations. She explained how this first major setback in her life was resolved as part of the Springer Nature Storytellers programme.

“I'm doing really proper theory – the most geeky physicist thing you can think of, pencil and paper, and lots of eraser, and even more coffee and tea on the side,” said Josefine Proll, Assistant Professor in the Department of Applied Physics at Eindhoven University of Technology. “And it's usually really fun and nice. It's a bit like being a detective.” 

Josefine studies nuclear fusion – an area of research that has the potential to solve the world energy crisis, providing an unending source of clean energy. Her research looks into turbulence, a phenomenon currently considered the main problem in fusion devices.

At a Springer Nature Storytellers programme event, Josefine told the story of how she became a fusion physicist and what happened when a major calculation error in a high-profile paper was discovered. 

The Storytellers programme harnesses the power of storytelling to help expand authors’ influence beyond their scholarly circles. As part of our commitment to the UN Sustainable Development Goals (SDGs), our recent focus for the programme has been on the food–energy–water nexus, hearing stories about related research from authors who’ve published with Springer Nature. 

The power of the sun on Earth

Josefine set the scene for her story, explaining that it started when she was mid-way through her PhD at the Max Planck Institute for Plasma Physics in Greifswald, Germany. She’d visited the institute as a child and it was there that she’d first learned of nuclear fusion.

“Nuclear fusion is the process that powers the stars and the sun,” she explained. “It's taking two light atoms and merging them, fusing them, and out comes a lot of energy. It’s been a dream of humanity for more than half a century to get it working on Earth because it could really solve the world's energy problems. It would be an energy source that doesn't produce CO2. And the fuel is abundantly there.” 

It was during her visit that Josefine decided she wanted to work on making nuclear fusion a reality. And by January 2012, she was back at the Max Planck Institute doing just that. 

“My research is about looking into the waves that can emerge in the fuel of our fusion reactor which is just a really hot gas we call the plasma,” she explained, “and these waves can lead to turbulence just like from an aeroplane.”

To make nuclear fusion happen on Earth, Josefine described how we need to put a ‘cage’ around the super hot gas to prevent it from touching the walls and melting them. In her work, they use a magnetic field as that cage.

“My research is about how you can make this magnetic cage into, maybe, a weird shape to prevent the waves and therefore the turbulence from even emerging,” Josefine continued. “[In 2012] I'm halfway through my PhD and things are looking good because the equations have shown something exciting. The equations have shown that if you build your magnetic cage in a very particular way, then an entire branch of waves can't exist and therefore not the turbulence.”

This discovery was cause for real excitement, not just for Josefine but for her supervisors as well. Little did she know, however, that it was about to cause turbulence of a whole different kind.

From fusion turbulence to personal turbulence

“We started writing a paper and we're submitting it to a fancy journal,” said Josefine. “The first round of reviewer comments comes back really positive, so it's really smooth sailing.” 

The problems began when they shared the work with colleagues. One colleague, in particular, came back to Josefine with bad news that would set off waves of personal turbulence.

“He tells us that our calculation is wrong,” she said. “You have to imagine it's this really big equation. We have this big numerator and this big denominator – [each of them is] several lines long. 

“And in one bit, this denominator can go to zero, which we hadn't seen. So we're dividing by zero. And this is a cardinal sin, right? You learn in school, that this is the one thing you're not supposed to do.” 

With the paper almost as good as accepted, this finding caused major panic. And for Josefine presented the biggest setback in her life so far. 

“[I was thinking], what will happen to it, will it be published with the mistake? Will we have to send a correction? Will everyone know of this mistake? I mean, it's super embarrassing, right? To divide by zero.”

Josefine started imagining scenarios where she would have to start a new PhD project and her dreams of becoming a fusion physicist suddenly looked in doubt. 

From theory to real reactor design

To Josefine – and her colleagues’ – relief, there was a happy ending to the drama. After only a few weeks, the person who found the mistake came back to them with a solution. 

“Apparently he had felt really guilty for breaking our calculation,” she explained. “He felt obliged to fix it. And he did. So, in a moment, all my personal and professional turbulence was just dissolved, magically.” 

They resubmitted the paper with the new calculation that delivered – essentially – the same result. It predicted that if you bent the magnetic cage of the reactor in a very specific way, the turbulence would be absent.  

Fast forward to a few years later and this theoretical prediction has been confirmed by experiment.

“Now whenever we're designing fusion reactors, we're taking my theory into account,” concluded Josefine, “which makes me really very proud.”

You can watch Josefine’s full story below: 

Visit our SDG Programme for more information about how we’re supporting the UN SDGs.

Josefine Proll is an Assistant Professor in the Department of Applied Physics at Eindhoven University of Technology.


Author: Guest contributor

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