US, WASHINGTON (ORDO NEWS) — When a fire extinguisher is operating, the carbon dioxide escaping from it forms ice-like crystals around the nozzle. This clearly demonstrates the physical principle that gas and plasma are cooled during expansion. The solar wind – a stream of helium-hydrogen plasma emanating from the corona – behaves the same. However, its cooling does not occur as intensively as physical laws predict.
In an article published in Proceedings of the National Academy of Sciences , physicists from the University of Wisconsin at Madison provide an explanation for the unusual properties of this stream. “People have studied the solar wind since it was discovered in 1959, but there are many important properties of this plasma that are still not entirely understood,” says Stas Boldyrev, lead author of the study. – Initially, the researchers thought that the solar wind should cool very quickly when moving away from the Sun, but satellite measurements show that when it reaches the Earth, its temperature is 10 times higher than expected. So, the fundamental question is: why is it not cooling down? ”
The solar wind consists mainly of electrons, protons and helium nuclei. This flux of particles is affected by magnetic fields generated below the surface of the sun. Electrons, like the lightest particles, move faster than others. Some of them, which have more energy, travel almost endless distances. Other electrons cannot tear away far from the star and at some point begin to return back: while their trajectories can noticeably change when interacting with other components of the solar wind.
“Particles whose velocity vector deviates from the lines of the magnetic field cannot move into the region of a strong field,” Boldyrev explains. This means that some electrons do not return back to the center of the star, but replenish the population of so-called trapped particles. “Their fate is to constantly jump back and forth,” the scientist concisely concludes.
It turned out that this effect underlies the phenomenon of slow cooling of the solar wind. And experiments on plasma retention helped scientists understand this. For experiments, special devices were built in which particles passed through a kind of “bottleneck” of the magnetic field, where the lines of force approached each other. Part of the electrons erupts further, but most of them are reflected back inside the machine.
A study of the processes taking place inside the plasma confinement apparatus showed that high-energy electrons – figuratively the hottest – can very slowly redistribute their energy over trapped electrons, heating them. According to scientists, these results are in good agreement with measurements of solar wind temperature.
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