Helicity barrier discovery sheds light on how solar plasma heats and flows

Helicity barrier discovery sheds light on how solar plasma heats and flows
by Sophie Jenkins
London, UK (SPX) Jul 09, 2025
Scientists have obtained the clearest evidence yet for a long-theorized mechanism that alters how energy is dissipated in the Sun's atmosphere, helping explain the high temperatures and rapid acceleration of the solar wind. Drawing on data from NASA's Parker Solar Probe, researchers investigated how turbulent energy behaves in the collisionless plasma near the Sun.

The study reveals that a phenomenon known as the helicity barrier significantly changes the process of turbulent dissipation. This barrier restricts the flow of energy down to smaller scales, modifying how energy converts into heat and helping explain why the Sun's outer atmosphere is hotter than its surface.

Jack McIntyre, a PhD student at Queen Mary University of London and lead author of the study, stated: "This result is exciting because, by confirming the presence of the 'helicity barrier', we can account for properties of the solar wind that were previously unexplained, including that its protons are typically hotter than its electrons. By improving our understanding of turbulent dissipation, it could also have important implications for other systems in astrophysics."

Researchers found that the helicity barrier becomes most pronounced under specific conditions-when magnetic fields dominate over plasma pressure and when turbulence becomes more imbalanced due to unequal wave propagation. These factors are especially common in the near-Sun environment that the Parker Solar Probe now routinely surveys.

Dr Christopher Chen, Reader in Space Plasma Physics and McIntyre's supervisor, added: "This paper is important as it provides clear evidence for the presence of the helicity barrier, which answers some long-standing questions about coronal heating and solar wind acceleration, such as the temperature signatures seen in the solar atmosphere, and the variability of different solar wind streams. This allows us to better understand the fundamental physics of turbulent dissipation, the connection between small-scale physics and the global properties of the heliosphere, and make better predictions for space weather."

Because many hot, low-density plasmas in space share similar properties with the solar wind, these findings offer insights applicable across astrophysical environments. Observing the helicity barrier directly in the solar wind offers a unique opportunity to probe how energy converts into heat in extreme, collisionless systems.

Research Report:Evidence for the helicity barrier from measurements of the turbulence transition range in the solar wind