China studies a possible mechanism for heating the solar corona — ScienceAlert
Researchers in Shanghai conducted a laboratory experiment with laser plasma that demonstrated a process of converting magnetic energy into heat. It may help explain part of the extremely high temperature of the solar corona — the Sun’s outer atmosphere, ScienceAlert reports.
The temperature of the Sun’s visible surface is about 5,500 °C, while the corona can heat up to more than one million degrees Celsius. Numerous small flares, or nanoflares, are considered one possible source of such heating. The new study focused on a possible mechanism behind their occurrence.
Experiment with laser plasma
The team, which included Wei Sun of the China Institute of Atomic Energy and Yongli Ping of Beijing Normal University, used the Shenguang-II laser facility in Shanghai. Four laser beams were directed at a plastic target with small wavy irregularities. Pulses lasting one billionth of a second turned the target material into plasma.
As the plasma expanded and slowed down, finger-like and mushroom-like structures emerged at its boundary. This phenomenon is known as the Rayleigh-Taylor instability. The plasma also generated its own magnetic fields around these structures, with the fields in neighboring areas pointing in opposite directions.
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Plasma heating
Computer modeling showed that the expanding structures brought the magnetic fields closer together, allowing them to reconnect. During such magnetic reconnection, stored energy is released and heats the plasma.
For comparison, the scientists repeated the experiment with a smooth plastic target. In this case, the plasma flow was more uniform and did not form the characteristic finger-like structures. Based on X-ray radiation, the researchers estimated the electron temperature: in the experiment with the wavy surface, it reached about 820,000 °C, nearly twice the figure for the smooth target.
In a separate computer simulation in which magnetic fields were not allowed to form, the additional heating largely disappeared. The authors suggest that similar conditions may arise on the Sun during coronal rain, when relatively cold and dense plasma descends through the surrounding atmosphere. At the same time, the laboratory plasma was much denser, and the process occurred much faster than the proposed solar nanoflares. The study’s results were published in the journal Physical Review Letters.
