In many areas of the solar atmosphere, including prominences, and many other astrophysical systems the majority of the fluid is neutral with only a small fraction being plasma. As with fully ionized plasmas, plasmas that are only partially ionized can be subject to flow instabilities which result in turbulence developing in the plasma. However, the coupling between the neutral component of the fluid and the magnetic field is not perfect, with the coupling coming as a result of collisions between neutral and charged species. The consequence of this is the fluids are strongly coupled to each other (resulting in the neutrals strongly feeling the Lorentz force) for slow dynamics, but if dynamic motions are quick enough the neutral fluid will not feel the magnetic field and behave purely hydrodynamically.

In this study we performed an extremely high-resolution 2D calculation, which allowed the dynamics at both coupled and decoupled scales to be simultaneously resolved. The basic set up had a velocity and density jump and a magnetic field aligned with the flow. The fluid was only 1% ionized.

The most surprising results of this study came from the thermodynamics. We found that heat transfer in the system could occur strongly across the magnetic field because the neutral fluid

How turbulent heating occurred also threw up a surprise. In standard turbulence, it is normally the smallest scales which drive the dissipation, but we found the frictional heating in partially ionized plasma is determined by the larger vortex scale instead of the small scale.

Based on results published in “Ion-neutral decoupling in the nonlinear Kelvin—Helmholtz instability: Case of field-aligned flow” by Andrew Hillier, Physics of Plasmas (2019). (The article can be accessed at https://doi.org/10.1063/1.5103248.)