= Lundquist liquid-metal Alfvén wave experiment
{c}
{title2=1949}
<Stig Lundquist>, the author printed as S. Lundquist, reported an early laboratory test in 1949. The apparatus used <mercury (element)> in a stainless-steel cylinder, a vibrating disk, and a floating mirror to indicate the motion at the liquid surface. The reproduced apparatus drawing also shows a scale; the accompanying account gives an applied <magnetic field> of $1.3\,\mathrm T$.<Numerical investigations of rotating MHD in a spherical shell by Andrey Sheyko>[Andrey Sheyko, Numerical investigations of rotating MHD in a spherical shell (2014), p. 8, Figure 1.4 and following paragraph; reproduction of Lundquist's apparatus]{ref}
The imposed <magnetic field> ran along the cylinder, while the bottom disk oscillated to excite azimuthal motion. Varying the drive <frequency> sought a <standing wave> <resonance>. A later authored experimental account describes this as an early hint: the <resonance> peak was not reached, and magnetic damping was substantial.<Torsional Alfvén waves in a dipolar magnetic field: experiments and simulations by Z. Tigrine and others>[2019, Section 1, paragraph beginning “Only a few laboratory experiments”: mercury vessel, bottom crenelated disk, resonance search and unreached peak]{ref} The experiment therefore tested a bounded azimuthal shear disturbance, related to a <torsional Alfvén wave>, rather than an infinite <plane wave> or a compression-driven <magnetosonic wave>.
\Image[/alfven-wave-liquid-mercury-test.png]
{title=Functional chain of Lundquist's early mercury Alfvén-wave test}
{description=An original functional schematic of the <mercury (element)> vessel, axial <magnetic field>, bottom disk excitation and surface mirror readout. It is not a dimensional reconstruction. The <frequency> scan sought a <standing wave> <resonance>; the early experiment did not establish a resolved peak.}
The <magnetic field> provides the controlled physical parameter: the ideal <Alfvén wave> prediction makes a propagation speed proportional to its strength, while a <resonance> also depends on the vessel's <boundary conditions>. A quantitative test must compare the driven response with finite-<electrical conductivity> theory and account for mechanical coupling and wall losses. An observed surface motion alone cannot distinguish all these mechanisms. The reproduced apparatus account gives neither a numerical drive <frequency> nor a field-off comparison. Lundquist's paper itself calls the experiment preliminary and proposes further investigations.<Experimental Investigations of Magneto-Hydrodynamic Waves by Stig Lundquist>[Abstract, final sentence: preliminary experiment and proposed investigations]{ref}
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