27-01-2025
A Brand New Kind of Fusion Reactor Just Went Online
Many tokamaks use what is called positive triangularity plasma to produce energy, but past experiments have found that the inverse of this triangularity could be more stable.
A new compact tokamak designed to contain negative triangularity plasma is officially online in Spain.
Called the SMall Aspect Ratio Tokamak (SMART), this reactor is part of the University of Seville's effort to not only make fusion energy possible, but also economically competitive for grid applications.
Bottling the Sun—a.k.a. fusion energy—comes in many shapes and sizes. Some of these shapes rely on 192 lasers to blast a small pellet of fuel, while others use donut-shaped (or toroidal) monster machines to try and maintain super-hot plasmas long enough to induce fusion. But the differences are more than just mechanical—even the very shape of the plasma can have profound differences in performance.
Engineers of tokamaks (those donut-shaped monster machines) use a term known as 'triangularity' to describe the plasma's deviation from an oval shape. Most tokamaks use positive triangularity—the plasma's cross-section looks like the letter 'D,' with the curved part of the plasma occurring along the outer wall. However, some tokamaks, including the DIII-D tokamak in San Diego, have now experimented with the inverse shape known as negative triangularity.
'This research showed that negative triangularity plasmas are free of potentially damaging instabilities in the edge region of the plasma without sacrificing fusion performance,' the U.S. Department of Energy reported in March of 2024. 'This suggests that negative triangularity shaping stabilizes instabilities in the plasma edge.'
Now, a new and compact fusion reactor in Spain—the SMall Aspect Ratio Tokamak, or SMART—is further experimenting with negative triangularity at the Plasma Science and Fusion Technology Laboratory of the University of Seville. The reactor has officially achieved first plasma, and preliminary results have been reported in the journal Nuclear Fusion.
The core concept behind nuclear fusion is keeping plasma hot enough for long enough to bootstrap nuclear fusion reactions—pumping out more power than the reactor originally invests. However, at high temperatures and densities, the plasma can develop gradients that can evolve into full-blown instabilities known as edge localized modes (ELMs), which can damage the reactor wall. With the discovery that negative triangularity limits the development of these highly-energetic ELMs, the hope is that reactors using this technique will be able to maintain high temperatures for longer.
This is where SMART comes in, as it's the first compact tokamak designed to operate at fusion temperatures using negative triangularity. While that may seem like a pretty esoteric accolade, its operation is drawing interest around the world.
'This is an important achievement for the entire team as we are now entering the operational phase of SMART,' Manuel García-Muñoz, principal investigator of the study, said in a press statement. 'The SMART approach is a potential game changer with attractive fusion performance and power handling for future compact fusion reactors.'
SMART is part of the University of Seville's Fusion2Grid strategy, which aims to design fusion energy for future power plants. While achieving this initial plasma is only a first step, the team also hopes to make fusion energy economically viable, which is likely a goalpost many years into the future. But as more and more fusion reactors come online, humanity's fusion future is beginning to take shape.
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