Researchers at the China Institute of Atomic Energy and Beijing Normal University simulated solar explosions in a laboratory setting by utilizing laser-produced plasma and magnetic fields, a breakthrough published in Physical Review Letters, which may explain how the Sun’s corona maintains temperatures exceeding one million degrees Celsius.
Laser Beams and Plastic Targets at Shenguang-II
To investigate the mechanisms behind solar heating, the research team fired four overlapping laser beams at a plastic target with a finely rippled surface at the Shenguang-II laser facility in Shanghai. These pulses lasted a billionth of a second. They transformed material from the target into plasma, a state of matter containing electrically charged particles threaded by magnetic fields.
As this plasma expanded into the less dense air and slowed down, ripples at the boundary grew into fingers and mushroom-shaped structures via the Rayleigh–Taylor instability. This plasma generation created distinct magnetic fields around the fingers. Neighboring structures carried fields in opposite directions, setting up the exact conditions required for magnetic reconnection.
Electron Temperatures Reaching 820,000 Degrees Celsius
Computer simulations confirmed how the expanding fingers brought oppositely directed fields together, allowing them to reconnect and release stored magnetic energy as heat. When the researchers analyzed the X-rays emitted by the plasma, the peak electron temperature with the rippled target reached the equivalent of roughly 820,000 degrees Celsius.
For comparison, a control experiment using a flat plastic target produced a smoother plasma flow without the finger-like structures. That flat configuration yielded a peak electron temperature about half as high. A separate computer simulation that prevented magnetic fields from forming showed that the extra heating largely disappeared.
Implications for Nanoflares and Coronal Rain
Scientists have long sought to understand why the Sun’s outer atmosphere, the corona, is hundreds of times hotter than its visible surface, which sits at around 5,500 degrees Celsius. The new laboratory findings support the hypothesis that countless tiny flares, known as nanoflares, collectively help maintain the corona’s extreme temperature.
On the Sun, similar boundary conditions could arise during coronal rain, a phenomenon where relatively cool, dense plasma falls through the surrounding atmosphere. While the laboratory plasma was much denser and unfolded on a much shorter timescale than solar nanoflares, the experimental setup provides a physical framework to test how efficiently magnetic reconnection heats plasma.
