Magnetohydrodynamic flows in ducts with insulating coatings

Effective insulation of the electrically conducting channel walls leads to a tolerable magnetohydrodynamic (MHD) pressure drop of liquid metal flows in self-cooled fusion reactor blankets. Such insulation prevents closed current circuits over conducting walls and reduces the total current, which determines the pressure drop and flow distribution caused by the interaction of the flowing liquid metal and the strong plasma-confining magnetic field. Several kinds of insulation are currently under development. One is the so-called flow channel insert technique, where the insulating ceramic is protected against the liquid metal by thin steel sheets. Recently, direct insulating ceramic coatings have been proposed which resist corrosion during the whole operation time of a fusion blanket. It is not necessary that these coatings provide perfect insulation. Even a finite coating resistance is enough to reduce the pressure drop by orders of magnitude. The aim of this paper is to provide material researchers and blanket designers with sufficient data on MHD insulation requirements. Changes in insulation properties occurring during the lifetime of the blanket due to impurities, corrosion, irradiation damage, or the presence of small cracks can be allowed up to a certain limit. The increase in the pressure drop and the change in flowmore » pattern are quantified, if the coating resistance falls below required limits.« less