Generation of electric currents in the chromosphere via neutral-ion drag

TL;DR

This paper investigates how electric currents generated by neutral-ion drag in the low-ionization solar chromosphere can lead to significant heating, potentially explaining chromospheric and coronal temperature increases.

Contribution

It introduces a novel mechanism for electric current generation via neutral-ion drag in weakly ionized plasma, highlighting its role in chromospheric heating.

Findings

Magnetized electrons drift relative to ions, generating intense electric currents.

Resistive dissipation of currents heats electrons efficiently.

Temperature increases of 0.1-0.3 eV/km with altitude are possible.

Abstract

We consider the generation of electric currents in the solar chromosphere where the ionization level is typically low. We show that ambient electrons become magnetized even for weak magnetic fields (30 G); that is, their gyrofrequency becomes larger than the collision frequency while ion motions continue to be dominated by ion-neutral collisions. Under such conditions, ions are dragged by neutrals, and the magnetic field acts as if it is frozen-in to the dynamics of the neutral gas. However, magnetized electrons drift under the action of the electric and magnetic fields induced in the reference frame of ions moving with the neutral gas. We find that this relative motion of electrons and ions results in the generation of quite intense electric currents. The dissipation of these currents leads to resistive electron heating and efficient gas ionization. Ionization by electron-neutral impact does not alter the dynamics of the heavy particles; thus, the gas turbulent motions continue even when the plasma becomes fully ionized, and resistive dissipation continues to heat electrons and ions. This heating process is so efficient that it can result in typical temperature increases with altitude as large as 0.1-0.3 eV/km. We conclude that this process can play a major role in the heating of the chromosphere and corona