Actively circulated liquid metal divertor (ACLMD)

Shimada, Michiya; Hirooka, Yoshihiko*; Zhou, H.*

Tungsten is considered to be most promising candidate for divertor target material for fusion reactor. Although tungsten target can withstand the heat loads of ITER, the heat exhaust requirement for DEMO is much more demanding. Pulsive heat loads associated with disurption would melt the tungsten divertor target. Melting and subsequent resolidification will roughen the tungsten surface, significantly deteriorating the heat handling capability. Further, tungsten has a rather high DBTT (Ductile-Brittle-Transition temperature) of 400C. Neutron irradiation would further increase the DBTT, which could result in cracks. In view of these issues, liquid metal divertor is proposed, which is actively circulated with the Lorentz force introduced through the electrodes in the liquid metal. A modest flow speed of 0.3 m/s seems to be adequate for the heat load exhaust of DEMO. A simple treatment of MHD equation in a cylindrical geometry suggests that the requirements on the current and voltage are modest if the ramp-up of current is made slowly (e.g. in a minute), implying that the this concept is worth further study.