Numerical Study of Magnetic Island Coalescence Using Magnetohydrodynamics With Adaptively Embedded Particle-In-Cell Model

TL;DR

This paper introduces a hybrid MHD-Particle-In-Cell model with adaptive regions to efficiently simulate magnetic island coalescence, capturing kinetic effects with reduced computational cost compared to full kinetic models.

Contribution

The study develops and validates an adaptive embedded PIC approach within MHD simulations, effectively modeling kinetic physics in magnetic reconnection scenarios.

Findings

Good agreement between adaptive PIC, static PIC, and full PIC results.

Large adaptive PIC regions are necessary for accurate simulation.

Magnetic island coalescence is highly kinetic in nature.

Abstract

Collisionless magnetic reconnection typically requires kinetic treatments that are, in general, computationally expensive compared to fluid-based models. In this study, we use the magnetohydrodynamics with adaptively embedded particle-in-cell (MHD-AEPIC) model to study the interaction of two magnetic flux ropes. This innovative model embeds one or more adaptive PIC regions into a global MHD simulation domain such that the kinetic treatment is only applied in regions where kinetic physics is prominent. We compare the simulation results among three cases: 1) MHD with adaptively embedded PIC regions, 2) MHD with statically (or fixed) embedded PIC regions, and 3) a full PIC simulation. The comparison yields good agreement when analyzing their reconnection rates and magnetic island separations, as well as the ion pressure tensor elements and ion agyrotropy. In order to reach a good agreement among the three cases, large adaptive PIC regions are needed within the MHD domain, which indicates that the magnetic island coalescence problem is highly kinetic in nature where the coupling between the macro-scale MHD and micro-scale kinetic physics is important.