Determination of multichannel MHD velocity profiles from wall-potential measurements and numerical simulations

In the helium cooled lead lithium (HCLL) blanket concept the eutectic alloy PbLi is used as breeder material and the heat is removed by helium. The liquid metal flows in rectangular boxes, called breeder units (BUs), which are arranged in columns to form a blanket module. Experiments have been performed to study MHD flows in a HCLL blanket mock-up that consists of 8 BUs fed and drained by poloidal manifolds. Electromagnetic flow coupling of adjacent fluid domains, due to an exchange of electric currents, plays an essential role in determining the velocity distribution in the breeding zone. During experiments electric potential on the walls perpendicular to the magnetic field has been recorded. In general, the electric potential serves as approximate streamfunction of the flow if walls are thin and induced currents are small. However, if the walls of the mock-up are thick, as in the performed experiments, induced currents should be taken into account. In order to correctly interpret surface electric potential measurements in terms of velocity distribution inside the test-section, a comparison with numerical simulations is required. A procedure has been developed to derive global solutions for magnetohydrodynamic (MHD) flows and to predict the velocity distribution in the test-section starting from experimental potential measurements and by comparing them with numerical results.