MAGMA: a 3D, Lagrangian magnetohydrodynamics code for merger applications

TL;DR

MAGMA is a novel 3D Lagrangian MHD code using SPH with Euler potentials, ensuring divergence-free magnetic fields and demonstrating high conservation and accuracy through extensive multidimensional tests.

Contribution

The paper introduces MAGMA, a new Lagrangian MHD code based on SPH that employs Euler potentials for magnetic field evolution, ensuring divergence-free fields and improved conservation.

Findings

Excellent conservation properties demonstrated.

Euler potentials outperform previous magnetic SPH formulations.

Code validated through extensive multidimensional tests.

Abstract

We present a new, completely Lagrangian magnetohydrodynamics code that is based on the SPH method. The equations of self-gravitating hydrodynamics are derived self-consistently from a Lagrangian and account for variable smoothing length (``grad-h''-) terms in both the hydrodynamic and the gravitational acceleration equations. The evolution of the magnetic field is formulated in terms of so-called Euler potentials which are advected with the fluid and thus guarantee the MHD flux-freezing condition. This formulation is equivalent to a vector potential approach and therefore fulfills the $\vec{\nabla}\cdot\vec{B}=0$-constraint by construction. Extensive tests in one, two and three dimensions are presented. The tests demonstrate the excellent conservation properties of the code and show the clear superiority of the Euler potentials over earlier magnetic SPH formulations.