When the tokamak is turned on, something magical happens in the confines of its reinforced belly. Plasma born from heavy hydrogen blooms in a bright pink color, spinning and twisting around the doughnut-shaped chamber. Then, tiny grains of lithium fall into the maelstrom, glowing like scarlet fairy dust before bursting into rays of vivid green-yellow light. Thanks to a high-speed color camera, we can observe this process in action as the plasma heats up inside the Tokamak Energy. ST40, which creates some of the conditions that future tokamaks will use to break apart atomic nuclei and generate the fusion energy that could one day power the world. But it’s not just the splendor of the view that is a marvel. Plasma fusion has a long way to go before it is close to being ready for practical application, and observing the path of burning lithium could help physicists overcome one of the main obstacles facing the technology: how to safely vent the tremendous heat that escapes. a fusion plasma. frameborder=”0″ enable=”accelerometer; autoplay; writing on clipboard; encrypted media; gyroscope; picture in picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” enablefullscreen> A tokamak needs to confine plasma at temperatures of millions of degrees to force atomic nuclei together. But that confinement isn’t easy, and some of the tremendous spinning energy inevitably escapes from the confined plasma. It has to go somewhere, so tokamaks are designed to channel as much of that escaping heat as possible into components called diverters. Currently, The tokamak experiments are relatively short, however, in a future fusion power plant, those components will have to withstand harsh heat loads for long periods without rapidly disintegrating. The diverter heat load is such an important issue that it is one of the key factors shaping the design of future spherical tokamak power plants. In experiments with ST40, researchers have measured heat fluxes of up to 150 megawatts per square meter. Tokamaks have been equipped with high-speed, high-resolution cameras for almost as long as tokamaks have existed. High-speed color imaging is not entirely new either: a color camera was implemented in Russia’s T-11M tokamak in 2014, as described in a 2016 paper. T-11M tokamaks are lithium droplets ejected from the limiter during an instability, traveling at about 100 meters per second (Lazarev et al. al., Fusion Eng. Des., 2016). 16,000 fps. This is what you’re looking for. Normally, impurities in the plasma running inside a fusion reactor can create major problems, causing heat to radiate more quickly, which cools the plasma and can interfere with the conditions needed for fusion. to sustain fusion conditions. This is the idea behind an experimental operating regime called X-point radiator, or XPR. The comparatively colder plasma around its edge. The pink glow comes from deuterium gas fed to the tokamak, which emits a combination of red and blue wavelengths. positively charged ions. These Li⁺ ions emit a distinctive greenish-yellow light. And because they are now electrically charged, the lithium ions follow the magnetic field, turning those vivid yellow-green streaks into a bright tracer of the otherwise invisible field lines that confine the plasma. A temperature map of the tokamak would be relatively easy to obtain even in black and white. and ions in different plasma conditions, revealing where lithium travels and how deeply it penetrates. Combined with spectroscopy, which precisely identifies the wavelengths of light that are emitted, high-speed imaging gives physicists another way to see if impurities are radiating energy where they want it. If not, physicists can change the conditions and try again, learning how to keep the cooling where they want it. And there are early signs that the XPR approach could work. In preliminary results from the experiments at ST40, the researchers report that they have been able to produce a radiant region that moves across the Experiments using lithium and neon to further reduce the heat load. Computer models suggest that lithium could be particularly useful because it may be possible to concentrate it around the diverter, where its cooling effect is desired, without allowing enough of it upstream to degrade the performance of the plasma core. And Tokamak Energy plans to push the idea further to examine what happens at the edge of the plasma. approaching the future of fusion. This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. While we take pride in our process, we’re human. If you spot an error, please let us know.
