Experimental evidence of Alfv\'en wave propagation in a Gallium alloy

TL;DR

This study provides experimental and numerical evidence of Alfvén wave propagation in a liquid gallium alloy under high magnetic fields, demonstrating resonance and wave reflection phenomena.

Contribution

It is the first to experimentally observe Alfvén waves in galinstan and to generate and track poloidal disturbances without interference from outside the domain.

Findings

Confirmed Alfvén wave propagation in galinstan at high magnetic fields

Observed resonance of Alfvén modes in liquid metal

Numerical simulations successfully reproduced experimental results

Abstract

Experiments with a liquid metal alloy, galinstan, are reported and show clear evidence of Alfv\'en wave propagation as well as resonance of Alfv\'en modes. Galinstan is liquid at room temperature, and although its electrical conductivity is not as large as that of liquid sodium or NaK, it has still been possible to study Alfv\'en waves, thanks to the use of intense magnetic fi elds, up to 13 teslas. The maximal values of Lundquist number, around 60, are similar to that of the reference experimental study by Jameson [1]. The generation mechanism for Alfv\'en waves and their refl ection is studied carefully. Numerical simulations have been performed and have been able to reproduce the experimental results despite the fact that the simulated magnetic Prandtl number was much larger than that of galinstan. An originality of the present study is that a poloidal disturbance (magnetic and velocity fields) is generated, allowing us to track its propagation from outside the conducting domain, hence without interfering.