Path-setting findings demonstrate for the first time a novel regime for confining heat in stellarators. The demonstration could advance the twisty design as a blueprint for future fusion power plants.

Physicists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) working with Japanese researchers, made the observation on the Large Helical Device (LHD) in Japan, a twisty magnetic facility that the Japanese call a «heliotron.» The results demonstrated for the first time a novel regime for confining heat in facilities known as stellarators, similar to the heliotron. The findings could advance the twisty design as a blueprint for future fusion power plants.

Higher confinement

Researchers produced the higher confinement regime by injecting tiny grains of boron powder into the LHD plasma that fuels fusion reactions. The injection through a PPPL-installed dropper sharply reduced turbulent swirls and eddies and raised the confined heat that produces the reactions.

«We could see this effect very clearly,» said PPPL physicist Federico Nespoli, lead author of a paper that detailed the process in the journal Nature Physics. «The more power we put into the plasma the bigger the increase in heat and confinement, which would be ideal in real reactor conditions.»

Said David Gates, a principal research physicist at PPPL who heads the Advanced Projects Department that oversaw the work: «I am very excited about these excellent results that Federico has written up in this important paper about our collaborations with the team on the Large Helical Device. When we launched this project — the LHD Impurity Powder Dropper — in 2018 we had hopes that there might be an effect on energy confinement. The observations are even better than we expected with turbulence suppression across a large fraction of the plasma radius. I am very grateful to our Japanese colleagues for giving us the opportunity for our team to participate in these experiments.»

The findings also delighted Japanese researchers. «We are very pleased and excited to get these results,» said Masaki Osakabe, executive director of the LHD project and science adviser for nuclear fusion research for MEXT, the Japanese ministry responsible for nuclear power. «We are also honored to be collaborators with PPPL,» Osakabe said. «The findings revealed with this collaboration will provide a nice tool to control the high-performance plasma in a fusion reactor.»

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Materials provided by DOE/Princeton Plasma Physics Laboratory. Original written by John Greenwald. Note: Content may be edited for style and length.