Home » Fusion research returns to roots for magnet breakthrough

Fusion research returns to roots for magnet breakthrough

by Mark Cantrell
Scientists researching fusion power have gone back to their roots to develop not only the first stellerator built in 50 years – but the first to use permanent magnets.

Scientists researching fusion power have gone back to their roots to develop not only the first stellerator built in 50 years – but the first to use permanent magnets.

A stellerator is a “twisty” machine that confines plasma – the electrically charged fourth state of matter – to harness the fusion process that powers the sun and stars, and potentially generate clean electricity.

Researchers at the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have designed and built such a device using permanent magnets. They claim the experiemnt could show a simple way to build future devices for less cost, and allow for the testing of new concepts for future fusion power plants.

The device, known as MUSE, was detailed in papers published in the Journal of Plasma Physics, and Nuclear Fusion.

Tony Qian, lead author of the papers, and a graduate student in the Princeton Programme in Plasma Physics, based at PPPL, said: “Using permanent magnets is a completely new way to design stellarators. This technique allows us to test new plasma confinement ideas quickly and build new devices easily.”

Stellarators typically rely on complicated electromagnets that have complex shapes and create their magnetic fields through the flow of electricity. Those electromagnets must be built precisely with very little room for error, increasing their cost.

However, permanent magnets, like the magnets that hold art to refrigerator doors, do not need electric currents to create their fields. They can also be ordered off the shelf from industrial suppliers and then embedded in a 3D-printed shell around the device’s vacuum vessel, which holds the plasma.

Michael Zarnstorff, a senior research physicist at PPPL, and principal investigator on the project, said: “MUSE is largely constructed with commercially available parts. By working with 3D-printing companies and magnet suppliers, we can shop around and buy the precision we need instead of making it ourselves.”

The original insight that permanent magnets could be the foundation for a new, more affordable stellarator variety came to Zarnstorff in 2014. He added: “I realised that even if they were situated alongside other magnets, rare-earth permanent magnets could generate and maintain the magnetic fields necessary to confine the plasma so fusion reactions can occur, and that’s the property that makes this technique work.”

Original design

The stellerator concept was invested more than 70 years ago by PPPL founder, Lyman Spitzer, but it’s not the only concept for fusion facilities; another is the doughnut-shaped or coreed-apple-shaped tokamak design.

Tokamaks, such as PPPL National Spherical Torus Experiment-Upgrade, confine plasma using relatively simple magnets. For decades, this has been the preferred design for scientists around the world because of how well the devices confine plasma.

However, tokamaks also rely on magnetic fields created by electric currents running through the middle of the plasma, which create instabilities that interfere with the fusion reactions.

Stellarators, though, can operate without such currents, and therefore can run for indefinite periods of time. But their complicated magnets, which are hard to design and build, have for years meant that stellarators were not economical or practical options for fusion power plants.

That is why MUSE’s success in demonstrating that stellarators can operate using simple magnets is considered so important.

Amelia Chambliss is a graduate student at Columbia University’s Department of Applied Physics and Applied Mathematics. She helped design MUSE during a DOE internship at PPPL a few years ago.

She said: “Typical stellarator magnets are very difficult to machine because you have to do so very precisely. So, the idea that we can use lots of discrete magnets to do the job instead is very exciting. It’s a much easier engineering problem.”

Main image: A photo of MUSE, the first stellarator built at PPPL in 50 years and the first ever to use permanent magnets. Photo credit: Michael Livingston/PPPL Communications Department


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