Experimental evidence of Alfvén wave propagation in a Gallium alloy

Abstract

10p.International audienceExperiments with a liquid metal alloy, galinstan, are reported and show clear evidence of Alfvén wave propagation as well as resonance of Alfvén 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 Alfvén 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 Alfvén 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

Characterization of Flow-Magnetic Field Interactions in Magneto-Hydrodynamic Turbulence

“…The evolution toward equipartition is oscillatory with intermittent large fluctuations. Alboussiérre et al [1] have also observed these oscillations in their numerical and experimental work. (2) Over time, the amplitude and frequency of the oscillations in kinetic and magnetic energy decrease, partly due to kinetic energy decay, and partly due to the initially isotropic fluctuating velocity field adjusting to the directionality of the mean magnetic field (see Figs.…”

“…8. These effects on the contours are due to the Lorentz force exchange mechanism and are also indications of Alfvén waves [1,[54][55][56]. Transactions of the ASME Under the influence of a uniform magnetic field, MHD turbulence decay exhibits complex flow-magnetic field interactions due to the presence of Alfvén waves.…”

“…We plot the current density magnitude contours in Fig. 10 to show Alfvén wave propagation as shown in other studies [1,[54][55][56]. The time intervals yield the frequency observed in the nonlinear dynamical systems analysis in the previous section.…”

“…8. The changes observed at these different times are interpreted as passing of Alfvén waves [1,[54][55][56]. We plot the current density magnitude contours in Fig.…”

“…In magneto-hydrodynamic (MHD) turbulence, the flow field evolution is significantly influenced by the magnetic field through the so-called Lorentz force. Like many nonlinear systems, MHD turbulence displays a tendency toward energy equipartition [1][2][3][4][5]. The objective of this study is to examine the nonlinear coupling between velocity and magnetic field fluctuations for the purpose of developing a fundamental understanding of MHD turbulence.…”