Density-gradient-driven drift-wave turbulence in the solar corona

¹ Centre for Mathematical Plasma Astrophysics, KU Leuven 3001, Leuven, Belgium
² Dutch Institute for Fundamental Energy Research, 5612 AJ Eindhoven, The Netherlands
³ Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
⁴ Department of Physics & Astronomy, Ruhr-Universität Bochum, D-44780 Bochum, Germany
⁵ Institute of Physics, University of Maria Curie-Skłodowska, 20-031 Lublin, Poland
⁶ Faculty of Military Sciences, Netherlands Defence Academy, 1781 AC Den Helder, The Netherlands

^⋆ Corresponding author: m.brchnelova@mindef.nl

Received: 21 January 2025
Accepted: 23 April 2025

Abstract

Aims. The solar corona is a highly filamentary environment with density gradients of diverse scales and strengths. If perpendicular to the background magnetic field, such gradients give rise to drift waves (DWs) via the DW instability, leading to plasma heating and particle, heat, and momentum transport. Particularly in the context of the coronal heating and solar wind acceleration problems, it is instructive to study DWs to determine how they affect the budgets of the coronal plasma. This paper investigates density-gradient-driven DWs in the solar corona using non-linear gyrokinetic simulations, particularly fluctuation frequencies and coronal heating.

Methods. We used the gyrokinetic code GENE to simulate DW turbulence in slab geometry that represents a coronal loop. Simulations were carried out with the hydrogen mass ratio for cases with varying magnetic shear, density gradient scale lengths, and electron β, each covering ranges relevant to the corona.

Results. Frequencies between 0.1 mHz and a few hertz are obtained, with larger values possible for hotter and smaller structures. Turbulence spectra exhibit tails consistent with kinetic Alfvén wave turbulence. Particle acceleration in the parallel direction occurs, although this process only accounts for observed volumetric heating rates in regions with high gradients. In the perpendicular direction, conditions are generally such that fast stochastic heating can occur. Finally, the structure erosion timescales indicate that while DW turbulence can flatten gradients over time, most structures are expected to survive for days without additional driving.

Conclusions. Drift waves are expected to be unstable in the solar corona and can, especially when arising from strong density gradients, create an environment suitable for particle acceleration and plasma heating both parallel and perpendicular to the magnetic field on timescales of hours to days. Future modelling will assess DW behaviour in stronger gradients and in more complex configurations.