Analytic toroidal 3D MHD equilibria and steady Euler flows with invariant surfaces
Abstract
Families of explicit analytic solutions of the magnetohydrodynamic equilibrium equations are presented, equivalent to steady incompressible Euler flow. The solutions are non-axisymmetric and possess exact nested toroidal flux surfaces. No expansion is made in inverse aspect ratio or in the deviation from axisymmetry. The magnetic field and flux surfaces are given explicitly in Cartesian coordinates using elementary functions. The field, current density, and scalar pressure are smooth over the toroidal domain. The pressure gradient vanishes only on the magnetic axis. One family of solutions has uniform rotational transform ι=2, while another family has a sheared ι profile. These counterexamples to Grad's conjecture are valuable for understanding the existence and regularity of 3D equilibria and for testing numerical codes.
Related
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- Immortal Curve Shortening Flow on Analytic Surfaces
- Real-analytic standard families and rotational invariant curves
BibTeX
@misc{landreman2026analytic,
title = {{Analytic toroidal 3D MHD equilibria and steady Euler flows with invariant surfaces}},
author = {Matt Landreman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26742},
eprint = {2609.26742},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26742},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Analytic toroidal 3D MHD equilibria and steady Euler flows with invariant surfaces
AU - Matt Landreman
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.26742
UR - https://arxiv.org/abs/2609.26742
AB - Families of explicit analytic solutions of the magnetohydrodynamic equilibrium equations are presented, equivalent to steady incompressible Euler flow. The solutions are non-axisymmetric and possess exact nested toroidal flux surfaces. No expansion is made in inverse aspect ratio or in the deviation from axisymmetry. The magnetic field and flux surfaces are given explicitly in Cartesian coordinates using elementary functions. The field, current density, and scalar pressure are smooth over the toroidal domain. The pressure gradient vanishes only on the magnetic axis. One family of solutions has uniform rotational transform ι=2, while another family has a sheared ι profile. These counterexamples to Grad's conjecture are valuable for understanding the existence and regularity of 3D equilibria and for testing numerical codes.
ER -