Energetic electrons from a powerful process that underlies solar flares - explosive bursts of plasma particles that can disrupt satellites, cell phone service and powerlines on Earth - have been detected for the first time by an experiment by researchers at the Department of Astrophysical Sciences at Princeton University and the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL).
The demonstration marks a milestone in Princeton research on the science of plasma, the soup of electrons and atomic nuclei the laboratory studies. The far-reaching functions of plasma range from serving as fuel for fusion energy that drives the sun and stars to the role of plasma in fields as vast as astrophysics and as tiny as the nanofabrication of computer chips. The breakthrough experiment focused on magnetic reconnection, the separation and reconnection of the magnetic fields in plasma.
Researchers have long proposed a link between reconnection and energetic particles, but few had been directly observed. The Princeton experiment "mirrored what happens in space to see if it agrees with theory," said PPPL physicist Lan Gao, coauthor of a paper that details the findings in the journal Nature Physics. "In our experiment, we actually saw that energetic electrons come from reconnection."
The experimental platform, which Princeton researchers set up at the Omega laser facility at the University of Rochester, uses lasers to produce reconnection - a process that differs markedly from the magnetically driven process that is commonly studied. The result is highly accelerated electrons that mirror the acceleration of flaring solar particles.
Solar flare researchers from left: Hantao Ji, Abraham Diem, Lan Gao. (Photo by Elle Starkman)
The experiment confirmed a linkage between reconnection and "nonthermal" bursts - the uniquely high energy electrons stemming from flares and flare-like events, demonstrating the theory. "It's easy to generate theories but very hard to test them," said PPPL physicist Hantao Ji, a professor of astrophysical sciences at Princeton University and a coauthor of the paper. "Our experiment achieved that."
"Hantao and I have been working on this for nearly 10 years," said Lan Gao. "When magnetic field lines reconnect, they lose magnetic energy, and we wanted to show where that energy goes." It accelerates cosmic particles to really high energies, she said, and the experiment demonstrates the link.
Going forward, Lan Gao and Hantao Ji now plan to explore other proposed sources of accelerated particles in the cosmos, which could further increase understanding of solar flares and their impact on Earth.
Coauthors of the Nature Physics paper were researchers from PPPL, Princeton University, the University of Rochester, Lawrence Livermore National Laboratory, and Los Alamos National Laboratory, the University of Michigan, the University of Bucharest in Romania and Osaka University in Japan. Lead author Abraham Chien graduated from Princeton's Department of Astrophysical Sciences in 2021 and this work is part of his Ph.D. thesis project.
Support for this research comes from the DOE Office of Science (FES) through Princeton's Department of Astrophysical Sciences and also under the LaserNetUS initiative at the Jupiter Laser Facility and the Omega facility at the University of Rochester.
