Magnetic reconnection, a perplexing phenomenon, causes explosive occurrences throughout the universe, causing solar flares and space storms that can disrupt cell phone service and electrical power systems.
Now scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have detailed a roadmap for untangling a key aspect of this puzzle that could deepen insight into the workings of the cosmos.
Reconnection transfers magnetic field energy to particle eruptions in astrophysical plasmas by snapping apart and explosively rejoining magnetic field lines, a process that takes place within what are known as dissipation areas, which are generally much smaller than the regions they influence.
Stressed magnetic field
“Plasma doesn’t like reconnection,” said Hantao Ji, a PPPL physicist and Princeton University professor who is first author of a paper that details the roadmap in Nature Reviews Physics. “However, reconnection does happen when the magnetic field is sufficiently stressed,” he said.
“Dissipation scales are tiny whereas astrophysical scales are very large and can extend for millions of miles. Finding a way to bridge these scales through a multiscale mechanism is a key to solving the reconnection puzzle.”
The roadmap outlines the role of developing technologies with multiscale capabilities, such as the Facility for Laboratory Reconnection Experiment (FLARE), a recently installed collaborative facility that is being upgraded and will probe aspects of magnetic reconnection previously unavailable to laboratory experiments.
FLARE can access wider astrophysical regimes than MRX with multiple reconnection points and measure the field geometry during reconnection. Understanding this physics is important for predicting how reconnection proceeds in solar flares.
William Daughton
Simulations on upcoming exascale supercomputers, which will be 10 times faster than present processors, will supplement these tests.
“The hope is for FLARE and exascale computing to go hand-in-hand,” Ji said.
The working idea proposed by the PPPL roadmap is that many plasmoids, or magnetic islands, formed by reconnection along long plasma current sheets might span a wide range of sizes.
These plasmoids would be more intimately related to the affected reconnection zone, with multiscale laboratory studies planned to give the first tests of this idea as well as to evaluate opposing possibilities.
“Exascale will allow us to do more credible simulations based on high-fidelity FLARE experiments,” said PPPL physicist Jongsoo Yoo, a coauthor of the paper.
The increased size and power of the new machine its diameter will be twice that of the sports-utility-vehicle-sized Magnetic Reconnection Experiment (MRX), PPPL’s long-standing laboratory experiment and will enable scientists to replicate reconnection in nature more faithfully.
“FLARE can access wider astrophysical regimes than MRX with multiple reconnection points and measure the field geometry during reconnection,” said William Daughton, a computational scientist at Los Alamos National Laboratory and a coauthor of the paper. “Understanding this physics is important for predicting how reconnection proceeds in solar flares,” he said.
Key challenge
Innovating new high-resolution diagnostic systems free of constraining assumptions will be a crucial task for the upcoming trials. Once built, these devices will allow FLARE to expand on satellite observations made by the Magnetospheric Multiscale mission, a fleet of four spacecraft launched in 2015 to explore reconnection in the magnetosphere, the magnetic field that surrounds the Earth.
“Progress in understanding multiscale physics critically depends on innovation and efficient implementation of such diagnostics systems in the coming decade,” the paper said. The new findings will address open questions that include:
- How exactly does reconnection start?
- How are explosive plasma particles heated and accelerated?
- What role does reconnection play in related processes such as turbulence and space shocks?
Overall, “The paper lays out plans to provide the entire space physics and astrophysics communities with methods to solve the multiscale problem,” Yoo said. “Such a solution would mark a major step toward a more complete understanding of magnetic reconnection in large systems throughout the universe.”
Support for this work comes from the DOE Office of Science. Coauthors include Jonathan Jara-Almonte of PPPL and Ari Le and Adam Stanier of Los Alamos National Laboratory.
