spaceSpace and Physics

Here's How To Stop Your Nuclear Fusion Reactor From Melting


Jonathan O'Callaghan

Senior Staff Writer

Runaway electrons could pierce the walls of reactors like this, the Joint European Torus (JET). Eurofusion

Dust off the “nuclear fusion breakthrough” sign again, because scientists are reporting that another important step has been reached in achieving this futuristic technology.

Basically, two PhD physics students at the Chalmers University of Technology in Sweden have found out how to stop your nuclear fusion reactor being severely damaged by a particular phenomenon. That’s probably going to be pretty useful to all you nuclear fusion scientists.


Research describing the findings has been published in the journal Physical Review Letters.

It relates to something called runaway electrons. To get your fusion reactor up and running, you need to be able to sustain a super-hot plasma inside it. To do this, you need extraordinary high pressure and a temperature of about 150 million degrees.

If something goes wrong, however, and the fusion process stops, temperatures inside the reactor can drop dramatically. If this happens, runaway electrons – those that still retain the energy from the plasma – can suddenly accelerate up to high speeds, high enough to destroy the reactor wall.

“If they run into the wall of the reactor, then they could melt part of it, which would cause serious damage,” Linnea Hesslow, one of the two physicists, told IFLScience. “It’s predicted that several kilograms of wall material would be melted. You would need to repair the reactor wall.”


If your reactor is nice and healthy, then this is nothing you need to worry about. But on the off chance something goes wrong, you’d better be prepared to deal with runaway electrons.

That’s where Hesslow and her colleague, Ola Embréus, come in. They have found that you can decelerate runaway electrons by injecting heavy ions into the reactor, in the form of a gas or pellet, to act as “brakes”. Neon or argon are said to be good examples.

When the runaway electrons collide with these ions, which have a high charge in their nuclei, they encounter resistance and lose speed. After many collisions, the speed of the electrons becomes controllable and the fusion reactor can be saved for another day.

"The interest in this work is enormous,” said Professor Tünde Fülöp, the advisor to the two PhD students, in a statement. “The knowledge is needed for future, large-scale experiments and provides hope when it comes to solving difficult problems. We expect the work to make a big impact going forward.”


This research follows a number of other recent breakthroughs in nuclear fusion research. Scientists are getting better at controlling the plasma and also perfecting the designs for the reactors themselves. Perhaps one day soon, we’ll enjoy the tremendous benefits – such as clean and safe energy – that nuclear fusion promises.


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