Solar Flare in the Lab? Small Caltech Miracles Unlock Cosmic Secrets

Plasma travels along magnetic lines enclosed in the corona which pull it back to the surface of the sun, forming loop-like structures. Credit: NASA

Caltech researchers measured solar flares, and found that their structures resemble twisted ropes. When these ‘strings’ tighten, they break and release bursts of energy, shedding light on the behavior of real solar flares.

To measure solar flares the size of bananas, researchers at the California Institute of Technology (Caltech) have dissected the process by which these massive explosions shoot potentially dangerous particles and X-rays into the cosmos.

Corona loops are arches of plasma radiating from the surface of the sun, they are aligned with the magnetic lines. Magnetic field lines act as charged particle highways, guiding the movement of electrons and ions that comprise the plasma. These streaks, which can extend 100,000 kilometers above the sun, can last for minutes to hours. Loops often grow and evolve slowly but sometimes they can explode with enormous energy – billions of times stronger than the most powerful nuclear explosion on Earth – in space. This sudden burst of energy is called a solar flare.

Measuring the corona loop at the Bellan Lab. Credit: Caltech

Possible Threats from Solar Flares

Some of the energy in the flame takes the form of charged particles and “hard X-rays,” which are high-powered electromagnetic waves similar to those used to image bones in a doctor’s office. The Earth’s magnetism and atmosphere act as a shield to protect life on Earth from being struck by these energy currents, but they are known to disrupt communications and power grids. They also pose a constant threat to spacecraft and astronauts in space.

Research Methodology and Measurement

Although the fact that solar flares produce energetic particles and X-ray bursts has long been known, scientists are just beginning to piece together how they do it.

Researchers have two options for how and why loops form and change. The first is to see the sun and then hope to document it in enough detail to generate relevant information. The second is measuring the loops in the lab. Caltech’s Paul Bellan, a professor of applied physics, chose the latter.

Measuring the corona loop at the Bellan Lab. Credit: Caltech

In a lab on the first floor of the Thomas J. Watson, Sr., Applied Physics Laboratories on the Caltech campus, Bellan built a vacuum chamber with twin electrodes inside. To measure this, he charged a capacitor with enough energy to power the City of Pasadena for a few microseconds, then discharged it with electrodes to create a small solar corona loop.

Each loop lasts about 10 microseconds, and has a length of about 20 centimeters (cm) and a diameter of about 1 cm. But structurally, Bellan’s loops are similar to the real thing, giving him and his colleagues the chance to play and learn at will.

Each test uses as much energy as it takes a 100-watt light bulb for about a minute, and it only takes a few minutes to charge the capacitor up, said Bellan, senior author of the new paper on solar flares. recently published in the journal Natural Astronomy. Bellan captures each loop with a camera capable of capturing 10 million frames per second, and then studies the resulting images.

New discoveries and insights

Among the recent discoveries is that the solar corona loops do not appear to be a single structure, but are made up of loosely woven threads that resemble a giant rope.

“If you cut a piece of rope, you can see that it is made of individual strands,” said Yang Zhang, a graduate student and lead author of the book. Natural Astronomy paper. “Separate those threads, and you’ll see that they’re woven into smaller threads, and so on. Plasma loops seem to work the same way. “

Structural similarity between a real solar eclipse (top) and one created in Bellan’s lab (below). Credit: Bellan Lab

That structure, it turns out, is important for the generation of energetic particles and X-ray bursts associated with solar flares. Plasma is a powerful conductor of electricity – think of neon signs, which are filled with plasma and light up when electricity is passed. However, when too much current tries to pass through the solar corona loop, the structure is disrupted. The loop produces a kink—a corkscrew-shaped-instepped—and the individual strands begin to break. Each new broken cord then sheds weight on the remaining ones.

“Like an elastic band stretched too far, the loop gets longer and shorter until the threads just snap,” said Seth Pree, a postdoctoral researcher in applied physics and materials science, and co-author Natural Astronomy paper.

Correlations and Future Research

Studying the process microsecond by microsecond, the team noticed a negative voltage spike corresponding to the X-ray burst at the exact moment the string broke. This voltage spike is similar to a pressure drop that builds up at a pressure point in a water pipe. The electric field from this electrical spike accelerates the charged particles to extreme energies, then X-rays are emitted when the energetic particles fall.

In addition, Zhang combined images of solar flares and was able to document the kink instability similar to that created in the lab that was associated with the next X-ray burst.

Next, the team plans to explore how different plasma loops can be combined and rearranged in different configurations. They are interested in learning if there are explosive events during this type of interaction.

Reference: “Laboratory production of nanoflares from multiple woven plasma loops” by Yang Zhang, Seth Pree and Paul M. Bellan, 6 April 2023, Natural Astronomy.
DOI: 10.1038/s41550-023-01941-x

This research was funded by the National Science Foundation and the Advanced Research Projects Agency-Energy (ARPA-E).