Ideal evolution of MHD turbulence when imposing Taylor-Green symmetries

TL;DR

This study explores the development of potential singularities in ideal incompressible MHD turbulence using high-resolution simulations with Taylor-Green symmetries, revealing possible finite-time singularities.

Contribution

It introduces a symmetry-based computational approach and a novel analytical method to assess singularity formation in 3D ideal MHD turbulence.

Findings

Potential finite-time singularity cannot be ruled out.

High-resolution simulations show colliding current and vorticity sheets.

Analytical method assesses the validity of singularity scenarios.

Abstract

We investigate the ideal and incompressible magnetohydrodynamic (MHD) equations in three space dimensions for the development of potentially singular structures. The methodology consists in implementing the four-fold symmetries of the Taylor-Green vortex generalized to MHD, leading to substantial computer time and memory savings at a given resolution; we also use a re-gridding method that allows for lower-resolution runs at early times, with no loss of spectral accuracy. One magnetic configuration is examined at an equivalent resolution of $6144^3$ points, and three different configurations on grids of $4096^3$ points. At the highest resolution, two different current and vorticity sheet systems are found to collide, producing two successive accelerations in the development of small scales. At the latest time, a convergence of magnetic field lines to the location of maximum current is probably leading locally to a strong bending and directional variability of such lines. A novel analytical method, based on sharp analysis inequalities, is used to assess the validity of the finite-time singularity scenario. This method allows one to rule out spurious singularities by evaluating the rate at which the logarithmic decrement of the analyticity-strip method goes to zero. The result is that the finite-time singularity scenario cannot be ruled out, and the singularity time could be somewhere between $t=2.33$ and $t=2.70.$ More robust conclusions will require higher resolution runs and grid-point interpolation measurements of maximum current and vorticity.