New supercomputer simulations have successfully modeled a mysterious process believed to produce some of the hottest and most dangerous solar flares—flares that can disrupt satellites and telecommunications networks, cause power outages, and otherwise wreak havoc on the grid. And what researchers have learned may also help physicists design more efficient nuclear fusion reactors.
In the past, solar physicists have had to get creative when trying to understand and predict flares and solar storms. It’s difficult, to put it mildly, to simulate the surface of the sun in a lab. Doing so would involve creating and then containing an extended region of dense plasma with extremely high temperatures (between thousands of degrees and one million degrees Celsius) as well as strong magnetic fields (of up to 100 Tesla).
However, a team of researchers based in the United States and France developed a supercomputer simulation (originally run on Oak Ridge National Lab’s recently retired Titan machine) that successfully modeled a key part of a mysterious process that produces solar flares. The group presented its results last month at the annual meeting of the American Physical Society’s (APS) Plasma Physics division, in Fort Lauderdale, Fla.
Jackson Matteucci is one of the co-investigators of that group and a Ph.D. student in plasma physics at Princeton. He says the twisting, snapping, merging, and reconnecting of magnetic field lines in a solar prominence represent the mystery his group is trying to understand.
A solar prominence is a thread of hot plasma that stretches from the sun’s surface to its outer atmosphere, and can remain in place for days or months. So-called magnetic reconnection—which happens in solar flares and in a solar prominence—acts like a slingshot for high-energy particles from the sun’s surface. And it’s the ultimate source for many of the worst solar storms seen on Earth.
Matteucci says his group has, for one, simulated an experiment conducted in China and published in the journal Nature Physics in 2010. The researchers in China blasted a piece of aluminum with high-energy lasers and recorded the event with high-speed instruments, capturing the tiny, solar flare-like explosion at nanosecond time scales.
Matteucci says the researchers in China succeeded in creating so-called “fast reconnection”—in which a flare blasts off a tangled and twisted magnetic field line in a nanosecond or less. Fast reconnection had been very difficult to explain from computer and theoretical models of solar flares. The observations reported by the team in China had been very difficult to explain either theoretically or in a computer model. But Matteucci’s team successfully simulated the results in a paper published last year in the journal Physical Review Letters, and shared at the recent APS meeting.
“We’re now able to model the [China] experiment from the ground up,” Matteucci says. “We model the field generation, and we model the collision of the fields, and we model the reconnection. We’re able to get everything.”
To be clear, Matteucci’s group has not modeled an actual solar flare. However, the experiment in China captured high-speed, granular data of the moment-by-moment action of a simulated flare. So Matteucci’s team sees that group’s results—and its own simulations—as helping to elucidate what’s actually going on when a solar flare snaps off a tangled prominence and ejects hot plasma out into space—and in some rare but dangerous cases, right toward Earth.
Fast reconnection events also happen in plasmas inside nuclear fusion reactors, which can destroy the confinement of a fusion plasma. “It ruins your magnetic field topologies [in a fusion plasma],” Matteucci says. “Which is sort of everything in magnetically-confined fusion.”
Being able to simulate these events on a supercomputer is certainly a big step forward. But simulation doesn’t equate to theoretical understanding of the process. “Analytical work is still struggling to figure this out,” Matteucci says.
An important next step would be for theorists to develop a framework that solar physicists could then use to study the solar surface and perhaps predict solar flares and outbursts.
“If you have a good physical understanding,” Matteucci says, “You don’t have to rely on simulations all the time.”
So in a sense, the mystery of solar flares is still waiting to be solved. But it’s now one step closer to being reduced to some succinct—and, to grid and satellite operators, very important—equations on a piece of paper.