Kinetic instability of drift-Alfven waves in solar corona and stochastic heating

TL;DR

This paper investigates how density gradients in the solar corona excite drift-Alfven waves through kinetic effects, and how stochastic heating from these waves could significantly contribute to coronal heating, especially in regions with strong magnetic fields.

Contribution

It provides a kinetic theory analysis of drift-Alfven wave growth rates and explores the role of stochastic heating in coronal energy release, highlighting the importance of magnetic field strength.

Findings

Electrostatic drift waves have stronger growth rates than electromagnetic ones.

Stochastic heating energy density depends more on magnetic field strength than wave coupling.

Heating rates could surpass the energy needed for sustainable coronal heating.

Abstract

The solar atmosphere is structured and inhomogeneous both horizontally and vertically. The omnipresence of coronal magnetic loops implies gradients of the equilibrium plasma quantities like the density, magnetic field and temperature. These gradients are responsible for the excitation of drift waves that grow both within the two-component fluid description (in the presence of collisions and without it) and within the two-component kinetic descriptions (due to purely kinetic effects). In the present work the effects of the density gradient in the direction perpendicular to the magnetic field vector are investigated within the kinetic theory, in both electrostatic and electromagnetic regimes. The electromagnetic regime implies the coupling of the gradient-driven drift wave with the Alfven wave. The growth rates for the two cases are calculated and compared. It is found that, in general, the electrostatic regime is characterized by stronger growth rates, as compared with the electromagnetic perturbations. Also discussed is the stochastic heating associated with the drift wave. The released amount of energy density due to this heating should be more dependent on the magnitude of the background magnetic field than on the coupling of the drift and Alfven waves. The stochastic heating is expected to be much higher in regions with a stronger magnetic field. On the whole, the energy release rate caused by the stochastic heating can be several orders of magnitude above the value presently accepted as necessary for a sustainable coronal heating.