Magnetic Energy Conversion in MHD: Curvature Relaxation and Perpendicular Expansion of Magnetic Fields

TL;DR

This paper investigates magnetic energy conversion in MHD systems, focusing on curvature relaxation and perpendicular expansion, and compares their roles in magnetic reconnection and astrophysical jet instabilities.

Contribution

It introduces a perspective on magnetic energy conversion via CR and PE, quantifies their importance in specific MHD phenomena, and links these processes to particle energization.

Findings

CR and PE have different temporal and spatial evolution.

The importance of CR and PE reverses from growth to nonlinear stages.

PE generally contributes more to magnetic energy conversion.

Abstract

The mechanisms and pathways of magnetic energy conversion are an important subject for many laboratory, space and astrophysical systems. Here, we present a perspective on magnetic energy conversion in MHD through magnetic field curvature relaxation (CR) and perpendicular expansion (PE) due to magnetic pressure gradients, and quantify their relative importance in two representative cases, namely 3D magnetic reconnection and 3D kink-driven instability in an astrophysical jet. We find that the CR and PE processes have different temporal and spatial evolution in these systems. The relative importance of the two processes tends to reverse as the system enters the nonlinear stage from the instability growth stage. Overall, the two processes make comparable contributions to the magnetic energy conversion with the PE process somewhat stronger than the CR process. We further explore how these energy conversion terms can be related to particle energization in these systems.