This article presents an experimental study of magnetohydrodynamic convection in a
tall vertical slot under the influence of a horizontal magnetic field. The test fluid is an
eutectic sodium potassium Na22K78 alloy with a small Prandtl number of Pr ≈ 0:02.
The experimental setup covers Rayleigh numbers in the range 103 [lsim ] Ra [lsim ] 8×104
and Hartmann numbers 0 < M < 1600. The effect of the magnetic field on the
convective heat transport is determined not only by damping as expected from
Joule dissipation but also, for magnetic fields not too strong, the convective heat
transfer may be considerably enhanced compared to ordinary hydrodynamic (OHD)
flow. Estimates of the isotropy properties of the flow by a four-element temperature
probe demonstrate that the increase in convective heat transport accompanies the
formation of strong local anisotropy of the turbulent eddies in the sense of an
alignment of the main direction of vorticity with the magnetic field. The reduced
three-dimensional nonlinearities in non-isotropic flow favour the formation of largescale
vortex structures compared to OHD flow, which are more effective for convective
heat transport. Along with the formation of quasi-two-dimensional vortex structures,
temperature fluctuations may be considerably enhanced in a magnetic field that is
not too strong. However, above Hartmann numbers M [gsim ] 400 the formerly strongly
time-dependent flow suddenly becomes stationary with an extended region of high
convective heat transport at stationary flow. Finally, for very high Hartmann numbers
the convective motion is strongly suppressed and the heat transport is reduced to a
state close to pure heat conduction.
Dominance of convective heat transport in the core of TFTR (Tokamak Fusion Test Reactor) supershot plasmas
