South Korea’s Artificial Sun Is Taking an Enormous Step Forward
Now that the fusion industry has reached the holy grail known as “ignition,” the next major challenge is designing components that can withstand plasma many times hotter than the Sun.
One such component—called the divertor—handles the hottest surface temperatures in the fusion devices known as tokamaks, and the Korea Superconducting Tokamak Advanced Research (KSTAR) just upgraded its divertor from carbon to tungsten to withstand these hot temperatures for longer.
A tungsten divertor is what will be used on the future International Thermonuclear Experimental Reactor (ITER) when it goes online next year, so KSTAR will provide invaluable data.
While the fusion industry eagerly awaits the International Thermonuclear Experimental Reactor (ITER)’s first plasma—tentatively scheduled for 2025—other, smaller reactors around the world are putting in groundbreaking work to prepare for this next-gen energy project. One of those reactors is located in Daejeon, South Korea, and is known as the Korea Superconducting Tokamak Advanced Research reactor (KSTAR).
Since 2008, KSTAR has tested fundamental concepts of fusion energy—the physics that powers our Sun—by producing 100 million degree Celsius plasma that forces certain hydrogen isotopes to fuse, producing tremendous amounts of energy.
Creating super-hot plasma some seven times hotter than the Sun is only half the battle. The toroidal (aka donut) shaped reactor also needs to contain that plasma for long stretches of time, which is far from an easy feat. In September 2022, KSTAR reached its 100 million degree Celsius for a full 30 seconds—a good start, but not long enough to actually produce more energy than what’s required to heat the plasma in the first place.
However, last week, the Korea Institute of Fusion Energy announced that a new upgrade will make KSTAR capable of containing plasma 10 times longer than its previous record by 2026. This is great timing, as any data gathered on KSTAR will also inform the internationally supported ITER project once it’s up and running. KSTAR will achieve these extended plasmas thanks to a new tungsten divertor that’s more capable of handling the immense heat flux found inside tokamak reactors.
“In KSTAR, we have implemented a divertor with tungsten material which is also the choice made in ITER,” Suk Jae Yoo, the president of the Korean Institute of Fusion Energy, said in a press statement. “We will strive to contribute our best efforts in obtaining the necessary data for ITER through KSTAR experiments.”
Divertors are immensely crucial for tokamak reactors. Installed at the bottom of the vacuum vessel, these devices manage exhaust and impurities, and need to withstand the highest surface heat loads. Previously, the KSTAR tokamak used a carbon-based divertor, as carbon has a high melting point. The only problem, however, was that plasma particles had a tendency to get stuck to the carbon surface, which limited how long a reaction could last. Tungsten—with its similarly high melting point but larger atomic mass—avoids this problem, allowing KSTAR to create reactions that last minutes instead of seconds.
“For fusion, you have to do three things—you have to get enough particles together, you have to get them hot enough, and you need to hold them long enough for the reaction to take place,” Phil Ferguson, director of the Material Plasma Exposure eXperiment (MPEX) Project at Oak Ridge National Laboratory, told Popular Mechanics last year. The MPEX project tests fusion reactor components, especially the divertor, against longterm plasma exposure. “You need a material solution. Give me the materials that can hold this thing together, at temperature, to be efficient.”
As the era of understanding the science that powers fusion comes to a head, unlocking this ultimate energy source will now be one of the greatest tests of engineering in human history.
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