Magnetohydrodynamic experiments on cosmic magnetic fields

TL;DR

This paper reviews experimental and theoretical advances in understanding cosmic magnetic fields, focusing on liquid metal experiments demonstrating dynamo effects and magnetorotational instability, crucial for cosmic structure formation.

Contribution

It provides a comprehensive overview of recent experimental evidence and progress in studying cosmic magnetic field generation and MRI in laboratory settings.

Findings

Magnetic field self-excitation observed in liquid sodium experiments.

MRI-like modes detected in turbulent spherical Couette flow.

Evidence for MRI as the first instability in stable flows.

Abstract

It is widely known that cosmic magnetic fields, i.e. the fields of planets, stars, and galaxies, are produced by the hydromagnetic dynamo effect in moving electrically conducting fluids. It is less well known that cosmic magnetic fields play also an active role in cosmic structure formation by enabling outward transport of angular momentum in accretion disks via the magnetorotational instability (MRI). Considerable theoretical and computational progress has been made in understanding both processes. In addition to this, the last ten years have seen tremendous efforts in studying both effects in liquid metal experiments. In 1999, magnetic field self-excitation was observed in the large scale liquid sodium facilities in Riga and Karlsruhe. Recently, self-excitation was also obtained in the French "von Karman sodium" (VKS) experiment. An MRI-like mode was found on the background of a turbulent spherical Couette flow at the University of Maryland. Evidence for MRI as the first instability of an hydrodynamically stable flow was obtained in the "Potsdam Rossendorf Magnetic Instability Experiment" (PROMISE). In this review, the history of dynamo and MRI related experiments is delineated, and some directions of future work are discussed.