Energy in density gradient

TL;DR

This paper quantifies the energy stored in density gradients of inhomogeneous plasmas, revealing its potential to power heating mechanisms like drift wave instability in solar corona models.

Contribution

It calculates the energy in density gradients for specific profiles, linking inhomogeneity energy to plasma heating, especially in solar corona contexts.

Findings

Energy in density gradients can exceed energy losses in the corona.

Moderate density increases can store enough energy for heating.

Inhomogeneity energy can be converted into heat via drift wave instability.

Abstract

Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindric configuration. This is of practical importance for drift wave instability in various plasmas, and in particular in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.