A Switch for Artificial Resistivity and Other Dissipation Terms

TL;DR

This paper introduces a new magnetic resistivity switch for SPH simulations that detects shocks more reliably and reduces unnecessary dissipation, improving accuracy especially in weak magnetic fields.

Contribution

A novel shock detection switch based on magnetic field gradients that outperforms previous methods and can be adapted for other artificial dissipation terms.

Findings

More robust shock detection in weak fields

Less overall artificial dissipation

Successful generalization to other dissipation switches

Abstract

We describe a new switch to reduce dissipation from artificial resistivity in Smoothed Particle Magnetohydrodynamics simulations. The switch utilises the gradient of the magnetic field to detect shocks, setting alpha_B = h |gradB| / |B|. This measures the relative degree of discontinuity, and the switch is not dependent on the absolute field strength. We present results comparing the new resistivity switch to the switch of Price & Monaghan (2005), showing that it is more robust in capturing shocks (especially in weak fields), while leading to less overall dissipation. The design of this switch is generalised to create similar switches for artificial viscosity and thermal conduction, with proof of concept tests conducted on a Sod shock tube and Kelvin-Helmholtz instabilities.