Magnetoconvection in vertical channels with a liquid metal downflow and a strong transverse magnetic field*

Downward flows in vertical ducts and pipes with non-uniform wall heating and transverse magnetic field are studied experimentally and numerically. The work is motivated by the design of liquid metal blankets for tokamak fusion reactors. The configuration considered is related to the blanket module with poloidal channels, in which liquid metal is pumped downward and the main component of the magnetic field is perpendicular to the flow direction. Strong heating flux is deposited at the wall facing the reaction chamber. A peculiar manifestation of the magnetoconvection effect, which also has significant implications for the blanket design is that of anomalous high-amplitude low-frequency fluctuations of temperature that appear at strong heating and strong magnetic field. They have been observed in the recent experiments for various orientations toward gravity and magnetic field. The analysis of experimental data and DNS shows that in a vertical channel the fluctuations are caused by growth and quasi-periodic breakdown of the pairs of ascending and descending jets related to the elevator-mode thermal convection.