Scale dependence of energy transfer in turbulent plasma

TL;DR

This paper investigates how different measures of energy transfer in turbulent plasma vary with scale, revealing that they are concentrated near each other but dominate at different scales, with implications for understanding plasma heating.

Contribution

It provides a scale-dependent analysis of multiple energy transfer proxies in turbulent plasma, highlighting their spatial correlation and scale-specific dominance.

Findings

Energy dissipation proxies are spatially close but decorrelate over a few ion inertial lengths.

Different proxies dominate at different scales, with large scales for electromagnetic work and small scales for pressure-strain.

The third-order law applies mainly within the inertial range of turbulence.

Abstract

In the context of space and astrophysical plasma turbulence and particle heating, several vocabularies emerge for estimating turbulent energy dissipation rate, including Kolmogorov-Yaglom third-order law and, in its various forms, $\boldsymbol{j}\cdot\boldsymbol{E}$ (work done by the electromagnetic field on particles), and $-\left( \boldsymbol{P} \cdot \nabla \right) \cdot \boldsymbol{u}$ (pressure-strain interaction), to name a couple. It is now understood that these energy transfer channels, to some extent, are correlated with coherent structures. In particular, we find that different energy dissipation proxies, although not point-wise correlated, are concentrated in proximity to each other, for which they decorrelate in a few $d_i$(s). However, the energy dissipation proxies dominate at different scales. For example, there is an inertial range over which the third-order law is meaningful. Contributions from scale bands stemming from scale-dependent spatial filtering show that, the energy exchange through $\boldsymbol{j}\cdot\boldsymbol{E}$ mainly results from large scales, while the energy conversion from fluid flow to internal through $-\left( \boldsymbol{P} \cdot \nabla \right) \cdot \boldsymbol{u}$ dominates at small scales.