Fast reconnection in partially ionized plasma has important implications for the interstellar medium, the vast clouds of gas and dust that fill the cosmos between stars. The cold, dense regions of the interstellar medium where stars form are only very poorly ionized, and fast reconnection occurring within these regions can help remove magnetic fields that prevent star formation.
Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have now produced the first fully kinetic model of the behavior of plasma particles and found that fast reconnection can indeed occur in partially ionized systems.
Fast magnetic reconnection, the rapid convergence, separation and explosive snapping together of magnetic field lines, gives rise to northern lights, solar flares and geomagnetic storms that can disrupt cell phone service and electric power grids. The phenomenon takes place in plasma, the state of matter composed of free electrons and atomic nuclei, or ions, that makes up 99 percent of the visible universe. But whether fast reconnection can occur in partially ionized plasma — plasma that includes atoms as well as free electrons and ions — is not well understood.
“There is a whole class of partially ionized plasmas whose link to reconnection has not been well studied,” said physicist Jonathan Jara-Almonte, lead author of a paper in Physical Review Letters that reports the recent findings. “We have now demonstrated that fast reconnection can occur in partially ionized systems.”
Understanding when and where fast reconnection occurs remains an unsolved problem, and previous analytical predictions for partially ionized plasmas relied on extrapolating from fully ionized ones. The new simulations, performed on computers at Princeton University, demonstrated that the transition to fast reconnection occurs only when the current sheet is much thinner than predicted. The results suggest that the transport of plasma and heat is different in partially ionized plasmas and can alter how and when reconnection occurs.
These findings focus on reconnection on a very small scale, unlike the process that occurs in the solar chromosphere. Nonetheless, the simulation proved compatible with reconnection in the upper chromosphere as well as in small-scale laboratory experiments.
Article sourced; https://www.pppl.gov/news/press-releases/2019/02/confirming-little-understood-source-process-behind-northern-lights-and
