Nuclear fusion is a potential source of clean electricity that could have a myriad of uses that could help mitigate climate change. Fusion releases huge amounts of energy by combining light elements in the form of plasma. Plasma is the hot, charged state of matter composed of free electrons and atomic nuclei that makes up ninety-nine percent of the visible universe. Laboratories around the world are working on harnessing fusion reactions to create a virtually inexhaustible supply of safe and clean power to generate electricity.
Stellarators are twisty devices designed to reproduce the fusion energy that powers the sun and stars. They primarily rely on external magnetic fields to confine a plasma. The stellarator was invented by American scientist Lyman Spitzer of Princeton University in 1951. Much of its early development was carried out by his team at what became the Princeton Plasma Physics Laboratory (PPPL). PPPL has been working for over fifty years on developing the theoretical knowledge and advanced engineering to enable fusion to power the U.S. and the world.
Early in the development of stellarators, technical problems convinced researchers that they were not a viable route to commercial fusion. Research interest shifted to tokamaks instead. However, in time, tokamaks encountered serious technical problems and interest shifted back to stellarators. Stellarators can operate without the risk of damaging disruptions that doughnut-shaped fusion reactors called tokamaks encounter.
Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have found a mathematical shortcut that could help harness nuclear fusion for energy production on Earth. The new methodology permits researchers to more easily predict how well a stellarator can retain the heat crucial to fusion reactors.
The new technique measures how well a stellarator’s magnetic field can hold on to the fastest-moving atomic nuclei in the hot plasma. This is critical to boosting the overall heat and aiding the fusion reactions. The main question is how scientists can find a shape that holds in as much the heat as possible.
Alexandra LeViness is a graduate student in plasma physics at the PPPL. “This research shows that we can find the best magnetic field shape for confining heat by calculating something easier—how far the fast particles drift away from the curved magnetic field surfaces in the center of the plasma. This behavior is described by a number known as gamma C, which we discovered consistently corresponds with plasma confinement.” LeViness added that the shortcut advances future stellarator research. He went on to say that “because the more fast-moving particles that stay in the center of the plasma, the hotter the fuel and the more efficient the stellarator will be.”
Elizabeth Paul is an assistant professor of applied physics at Columbia University and a former presidential fellow at Princeton University. She said, “But using techniques like the one LeViness studied, we have been able to find magnetic configurations for stellarators that contain heat as well as tokamaks can. It's more challenging for stellarators, but LeViness has helped show that it's possible.