Hannes Alfven predicted the existence of a hydrodynamic wave in a perfectly conducting fluid in 1942. It took 6 years before this discovery was accepted and 10 years before Alfven waves were first observed in the laboratory. Now it is widely recognized that these waves are ubiquitous in space plasmas and are the means by which information about changing currents and magnetic fields are communicated. Alfven waves have been observed in the solar wind, are thought to be prevalent in the solar corona, may be responsible for parallel electric fields in the aurora, and can cause particle acceleration over large distances in interstellar space. They have also been considered as a candidate for heating thermonuclear plasmas and are potentially dangerous to confinement. Alfven waves have been difficult to observe in basic laboratory experiments because of their low frequencies and long wavelengths. In this paper we present a review of plasma Alfven wave experiments performed in recent years. The quality of the laboratory data have paralleled advances in plasma sources and diagnostics. In the past few years the quantum jump in data collection on the Freja and FAST missions have lead to the reevaluation of the importance of these waves in the highly structured plasma that was probed. Recent laboratory experiments have examined, in great detail, shear waves generated by filamentary currents in both spatially uniform and striated plasmas. Tone bursts, short pulses, and interference effects have been studied with emphasis on structures of the order of the skin depth, c/ωpe. These are features of significant interest to the space community. In fact, it appears that the phenomena observed in laboratory experiments show striking similarities to what has been observed in space. A comparison of these results will be given.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JA00161

Review of laboratory experiments on Alfvén waves and their relationship to space observations

Experiments with a liquid metal alloy, Galinstan, are reported and show clear evidence of Alfven wave propagation as well as resonance of Alfven 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 Alfven waves, thanks to the use of intense magnetic fields up to 13 T. The maximal values of Lundquist number, around 60, are similar to that of the reference experimental study by Jameson [J. Fluid Mech. 19, 513 (1964)]. The generation mechanism for Alfven waves and their reflection 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.

https://hal.archives-ouvertes.fr/hal-00602640/document

Experimental evidence of Alfven wave propagation in a Gallium alloy

Microwave Effects in Narrow-Gap Semiconductors (II)

Absorption, Fluorescence Emission, and Photophysics of Squaraines

Experiments with a liquid metal alloy, galinstan, are reported and show clear evidence of Alfven wave propagation as well as resonance of Alfven 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 Alfven 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 Alfven 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.

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

The present study reports on experimental investigations about the phase velocity diagrams of Alfven waves in the anisotropic solid-state plasma of bismuth. Alfven-wave transmission at 34 GHz and 4.2 K has been observed, using an interference technique of high sensitivity. The experimental results are in good agreement with a theoretical model given by Buchsbaum, which makes only use of the anisotropic mass tensor of bismuth.

Propagation of Alfvén waves in bismuth

The intrinsic carrier concentration in InSb was determined, between 246 and 370 K, by a helicon method consisting of a microwave interferometer at 34 GHz. The accuracy of the carrier concentration is between 1–2%. The influence of experimental parameters on the determination of the carrier concentration and the mobilities of both electrons and holes is discussed in detail. Comparing the data obtained for the carrier concentration with Hall effect measurements a small difference of the absolute values is found. The band-gap deduced is in agreement with the Hall effect measurements.

Determination of the intrinsic carrier concentration in InSb by helicon waves

The propagation of electromagnetic waves in solids with electron and hole energy surfaces of second order placed in a magnetic field is investigated The deduced dispersion relation is compared with measurements of the Alfven wave velocity in bismuth The theoretical and experimental results are in good agreement In particular, it is clearly shown that for special orientations of the magnetic field switching from one mode to the other occurs Parameters of the energy surfaces of bismuth are given by fitting the theoretical curves to the measured phase velocity diagrams

Magnetoplasma waves in anisotropic semiconductors and semimetals

We have investigated the propagation of Alfven waves in bismuth at 4.2 K using a microwave interferometer at 34.45 GHz and applying magnetic fields up to 1 Tesla. At certain angles between the external magnetic field and the direction of propagation of the Alfven waves in the crystal, we have observed intense oscillations of the amplitude and the phase of the interferometer curves. We explain these oscillations as due to a superposition of the two Alfven wave modes. The phase velocities of the two modes are calculated from the measurements. Comparing them with a general dispersion relation we find good agreement between the theoretical phase velocities and the experimental values.

H. Hinsch

Papers

Propagation of Alfvén waves in bismuth

Determination of the intrinsic carrier concentration in InSb by helicon waves

Magnetoplasma waves in anisotropic semiconductors and semimetals

Mode mixing of Alfvén waves in bismuth