Feasibility Study on Heat Pipes for Radio Frequency Antennas

The applicability of a heat pipe is investigated for the cooling of radio frequency antennas in fusion reactors operating at high temperatures. A heat pipe is a passive cooling device that transfers a large amount of heat through the liquid-vapor phase change and pumps the working fluid by the surface tension of the wick structure without moving parts. As the heat pipe is expected to operate near 1000 K, refractory metals or ceramics should be used for wall materials, and liquid metals are primarily considered as the working fluid. However, liquid metals are electrically conductive, and the strong magnetic field perpendicular to the flow direction imposes significant magnetohydrodynamic (MHD) flow resistance in addition to viscous friction, which impairs heat transfer performance.

Since a strong magnetic field is inevitable in magnetic confinement fusion reactors, materials with low electrical conductivity should be applied to wall coatings to reduce the MHD effect. Heat flux limitations at a magnetic field of 10 T and a condenser coolant temperature of 773 K are estimated using COMSOL multiphysics, which can capture the fully developed MHD wick flow, laminar/turbulent vapor flow, and heat transfer simultaneously. For simplicity, the generic heat pipe geometry of a straight horizontal cylinder with a length of 2 ft (0.6096 m) is employed. Optimal geometrical parameters are evaluated to meet radial evaporator/condenser heat fluxes greater than 0.1 MW/m², even under a strong MHD effect.