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Korean nuclear fusion reactor achieves 100 million°C for 30 seconds

An ongoing, stable experiment is the latest demonstration that nuclear fusion is turning from a physical problem into an engineering problem


September 7, 2022

The Korea Superconducting Tokamak Advanced Research Experiment

Korea Institute of Fusion Energy

A nuclear fusion reaction has lasted 30 seconds at temperatures over 100 million °C. While duration and temperature alone are not records, achieving heat and stability at the same time brings us one step closer to a viable fusion reactor – as long as the technique used can be scaled up.

Most scientists agree that viable fusion energy is still decades away, but increasing advances in understanding and results keep coming. An experiment conducted in 2021 produced a reaction energetic enough to sustain itself, drafting conceptual designs for a commercial reactor while work is underway on ITER’s large experimental fusion reactor in France.

utilities Yong-Su Na at Seoul National University in South Korea and his colleagues have managed to conduct a reaction at the extremely high temperatures required for a viable reactor, and the hot, ionized state of matter created in the device, 30 seconds to keep it stable.

Controlling this so-called plasma is vital. If it hits the walls of the reactor, it cools quickly, suffocating the reaction and causing significant damage to the chamber it is in. Researchers normally use different forms of magnetic fields to contain the plasma – some use an edge transport barrier (ETB), which forms plasma with a sharp cut-off in pressure near the reactor wall, a condition that stops the escape of heat and plasma. Others use an internal transport barrier (ITB) that creates a higher pressure closer to the center of the plasma. But both can cause instability.

Na’s team used a modified ITB technique on the Korea Superconducting Tokamak Advanced Research (KSTAR) device, achieving a much lower plasma density. Their approach appears to increase the temperature in the core of the plasma and decrease it at the edge, which is likely to extend the life of reactor components.

Dominic Power of Imperial College London says that to increase the energy produced by a reactor, you can make plasma very hot, make it very dense or increase the confinement time.

“This team finds that the density constraint is actually slightly lower than traditional operating modes, which isn’t necessarily a bad thing, as it’s offset by higher temperatures in the core,” he says. “It’s certainly exciting, but there’s a lot of uncertainty about how well our understanding of physics can be applied to larger devices. So something like ITER becomes much bigger than KSTAR.”

Na says low density was key, and that “fast” or more energetic ions in the plasma’s core — called fast-ion-regulated enhancement (FIRE) — are integral to stability. But the team doesn’t fully understand the mechanisms involved yet.

Only due to hardware limitations, the response was stopped after 30 seconds and longer periods should be possible in the future. KSTAR has now been shut down for upgrades, with carbon components on the reactor wall having been replaced with tungsten, which Na says will improve the reproducibility of experiments.

Lee Margetts at the University of Manchester, UK, says the physics of fusion reactors is well understood, but technical hurdles must be overcome before a working power plant can be built. This includes developing methods for extracting heat from the reactor and using it to generate electrical power.

“It’s not physics, it’s engineering,” he says. “If you just think about this from the point of view of a gas-fired or a coal-fired power plant, if you didn’t have anything to take the heat off, the people who work with it would say, we need to switch it off because it’s getting too hot and the plant will melt’, and that is exactly the situation here.”

Brian Appelbe at Imperial College London agrees that the scientific challenges lagging behind fusion research should be achievable, and that FIRE is a step forward, but commercialization will be difficult.

“The magnetic confinement fusion approach has a fairly long history of evolving to solve the next problem it faces,” he says. “But what makes me a little nervous or unsure is the technical challenges of actually building an economic power plant based on this.”

Reference magazine: Nature, DOI: 10.1038/s41586-022-05008-1

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