International audience

We report the results of a liquid metal Taylor-Couette experiment in the Rayleighstable regime under the influence of an azimuthal magnetic field.We observe that the resulting azimuthal magnetorotational instability (AMRI) from our experimental setup is significantly influenced by the thermal boundary conditions.Even a minimal radial heat flux leads to a symmetry breaking, which results in the AMRI waves traveling either upwards or downwards.We identify the thermal radiation by the central axial current as the heat source responsible for vertical convection in the liquid.Preliminary numerical investigations point towards an interaction between AMRI and thermal convection, which supports our experimental findings.

We investigate directional solidification of the melt with solid inclusions by means of a non-invasive imaging technique - neutron radiography. For the first time results have revealed particle trapping in the solidifying melt at macro scale. It is shown that particle solidification in volume can be achieved when liquid and solid phases form a mushy zone. Experiments were performed using a rectangular vessel containing tin (Sn) which was electromagnetically stirred and directionally solidified. Information about the recirculating flow was gathered by tracing 355-500 <em>μ</em>m gadolinium particles which visualize the flow field and the state of matter at any given time. The findings show that metallurgical challenges, e.g., stirring and homogeneously dispersing ceramic reinforcement material in metal matrix composites, could be solved by applying electromagnetic treatment while the melt is in a semi-solid state. Key words: directional solidification, mushy zone, neutron radiography, neutron imaging, particle trapping.