Physicists have succeeded in generating tiny solar flares in the laboratory

Our Sun regularly erupts in tongues of heat and fury so large that our own planet would be dwarfed by their size many times over. To better understand how they work, the researchers created a version that could fit in your lunchbox.

Using a device that turns powerful bursts of electricity into rope-like loops of plasma, a team of physicists modeled solar flares to study the powerful X-rays and energetic particles that streak through the solar system.

“Solar observations detect energetic particles and hard X-rays but cannot reveal the generating mechanism because particle acceleration occurs at a scale below the observational resolution. Thus, details of cross-scale physics that explain the generation of energetic particles and hard X-rays remain a mystery,” wrote a team led by physicist Yang Zhang of Caltech.

“Here we present observations from a laboratory experiment that simulates the physics of the solar coronal loop.”

The Sun is a very dynamic, bubbling ball of plasma fueled by nuclear fusion, so it’s no surprise that it’s up to some shenanigans. Powerful flares that eject light and particles into the surrounding space can affect the solar system over significant distances.

We are definitely feeling those effects here on Earth. The magnetosphere and atmosphere protect us from harsh, high-energy X-rays, but solar ejecta can interfere with satellites and spacecraft, including navigation and communications technology, and can cause grid fluctuations and disruptions electric. So scientists naturally want to know more about how the Sun creates and ejects matter in the first place.

But there is little we can glean from looking at the Sun itself; there is a limit to the scale of observations we can make using current technology. In order to study these fine details, physicists turned to the next best thing: replicating solar flares in a lab.

Caltech physicist Paul Bellan designed an experimental device specifically to generate structures called coronal loops. They are long, closed arcs of glowing plasma that shoot out of the solar photosphere, along magnetic field lines that jut out into the solar corona. These are often associated with increased solar activity, such as flares and coronal mass ejections.

Time series images of the experimental evolution of the plasma loop. (Zhang et al., Nat. Star.2023)

This device consists of gas nozzles, electromagnets and electrodes in a vacuum chamber.

First, the electromagnets are activated, generating a magnetic field in the vacuum chamber. Next, gas is injected into the electrode region.

A powerful millisecond-scale electrical discharge is then applied through the electrodes; this ionizes the gas, turning it into plasma which then forms a loop constrained by the magnetic field.

“Each experiment uses about as much power as it takes to run a 100-watt light bulb for about a minute, and it only takes a few minutes to recharge the capacitor,” says Bellan.

Each loop lasts only 10 microseconds and is very small, about 20 centimeters (7.9 inches) in length and one centimeter in diameter. But high-speed cameras record every moment of the loop’s generation and propagation, allowing the research team to analyze its formation, structure and evolution in detail.

Scientists have recently learned that coronal loops don’t just look like rope, they’re also structured like it. The new work allowed the team to understand the role this structure plays in the production of solar ejecta.

“If you dissect a piece of rope, you see that it’s made up of braids of individual strands,” says Zhang. “Separate those individual strands and you’ll see it’s braids of even smaller strands, and so on. Plasma curls seem to work the same way.”

And it turns out that these strands are responsible for the X-ray bursts. Because plasma is a strong conductor, current flows through the loops; but occasionally the current exceeds the capacity of a loop, like too much water flowing through a pipe.

When this happens, the team’s footage shows, a corkscrew-like instability develops in the loop and individual strands begin to snap, putting even more pressure on the remaining strands.

A comparison between coronal loops on the Sun (top) and in the lab (bottom), both developing fold instability and snapping, resulting in X-rays. (Zhang et al., Nat. Star.2023)

When a strand breaks, it produces a burst of X-rays, accompanied by a negative voltage spike, similar to the pressure drop in a water pipe with a kink. This voltage drop accelerates the charged particles in the plasma; when these particles decelerate, a burst of X-rays is emitted.

Scanning through images of coronal loops on the Sun, the researchers identified an instability similar to those seen in the lab that was also associated with a burst of X-rays, suggesting that – even if one was the size of a banana and that the other could comfortably swallow up our entire planet – both phenomena happened in the same way.

Future studies of the Sun will help unravel this process further, but it seems consistent with other studies that have shown how the breaking and reconnecting of magnetic field lines results in powerful bursts of energy. The team intends to follow up by studying the different ways coronal loops can merge and reconfigure to see what kinds of explosions this activity produces.

The research has been published in natural astronomy.

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