How to Confine Artificial Suns

Stellarators, twisty magnetic devices that aim to harness on Earth the fusion energy that powers the sun and stars, have long played second fiddle to more widely used doughnut-shaped facilities known as tokamaks. The complex twisted stellarator magnets have been difficult to design and have previously allowed greater leakage of the superhigh heat from fusion reactions.

Now scientists at the Max Planck Institute for Plasma Physics (IPP) in Germany, working in collaboration with researchers that include the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), have shown that the Wendelstein 7-X (W7-X) device in Greifswald, Germany, the largest and most advanced stellarator in the world, is capable of confining heat that reaches temperatures twice as great as the core of the sun.

PPPL physicist Novimir Pablant with computer simulation of W7-X magnetic coils and plasma.

A diagnostic instrument called the XICS, chiefly designed, built and operated by PPPL physicist Novimir Pablant in collaboration with IPP physicist Andreas Langenberg, is a key indicator of a sharp reduction of a type of heat loss called “neoclassical transport” that has historically been greater in classical stellarators than in tokamaks. Causing the troublesome transport are frequent collisions that knock heated particles out of their orbits as they swirl around the magnetic field lines that confine them. Contributing to the transport are drifts in the particle orbits.

A recent report on W7-X findings in Nature magazine confirms the success of the efforts of designers to shape the intricately twisted stellarator magnets to reduce neoclassical transport. First author of the paper was physicist Craig Beidler of the IPP Theory Division. “It’s really exciting news for fusion that this design has been successful,” said Pablant, a coauthor along with Langenberg of the paper. “It clearly shows that this kind of optimization can be done.”

David Gates, head of the Advanced Projects Department at PPPL that oversees the laboratory’s stellarator work, was also highly enthused. “It’s been very exciting for us, at PPPL and all the other U.S. collaborating institutions, to be part of this really exciting experiment,” Gates said. “Novi’s work has been right at the center of this amazing experimental team’s effort. I am very grateful to our German colleagues for so graciously enabling our participation.

Source: https://www.pppl.gov/