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This Breakthrough Could Fix the Fatal Flaw in Fusion Reactors

Photo credit: Denis Pobytov - Getty Images
Photo credit: Denis Pobytov - Getty Images

From Popular Mechanics


In the long road to nuclear fusion, scientists continue to confront one of the more prominent (and literal) bumps: edge localized modes (ELMs). These blobs form at the edge of a tokamak’s plasma swirl, caused by the interaction of the powerful, containing magnetic field and the sun-hot plasma.

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In the past, scientists have volunteered several solutions, including pulsating radio waves. But now, researchers from the Max-Planck-Institut für Plasmaphysik (IPP) in Germany have what they say is the first simulation of how ELMs form—making it easier to model the risks and the potential solutions.

“After extensive previous work, it has now been possible for the first time by means of computational simulations to identify the trigger responsible for the explosive onset of these edge instabilities and to reconstruct the course of several ELM cycles—in good agreement with experimentally observed values,” an IPP press release reads. The research on the simulation was accepted for publication in the journal Nuclear Fusion.

A tokamak is a donut-shaped machine whose chamber is designed to corral a stream of reactive, energy-producing matter in the plasma state. The stream of plasma is physically held by a magnetic field generated by electromagnets and superconductors, for example, that weave a basket of intersecting magnetism inside the chamber of the tokamak. The chamber itself isn’t designed to have million-degree plasma touch it, but so far, making a reliable magnetic field has proven to be extremely challenging.

When ELMs form, they can act like a kind of solar flare or geyser, splashing out from the main stream and disrupting the flow. The escaping plasma can drastically reduce energy output or even damage the equipment. And the scale of the impact depends on the size of the tokamak, for example. Experimenting with ELM risk factors at the massive international ITER fusion reactor could cost millions of dollars or more. A simulation could help scientists understand ELM mechanics without the costly side effects.


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Because the stakes are so high with fusion reactors, modeling even a split second worth of these interactions is hugely computationally expensive.

“Although the processes take place in a very short time, their simulation requires a great deal of computing effort,” the IPP statement explains. “This is because the simulation must resolve into small calculation steps both the short ELM crash and the long development phase between two ELMs—a calculation problem that could only be solved with one of the fastest supercomputers currently available.”

This answers the naturally consequent question: After decades of fusion research, why is this the first model of ELMs? Even supercomputers can only do so much, and modeling complex systems involves accounting for as many particles as possible during the smallest timeframes possible:

“The plasma theorists [...] were able to describe and explain the complex physical processes behind this phenomenon in detail: as a non-linear interplay between destabilising effects—the steep rise in plasma pressure at the plasma edge and the increase in current density—and the stabilising plasma flow.”

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