Analysis of Thin Film Liquid Metal Protection of Fusion Reactor Limtter/Divertor Surfaces

In an effort to prolong the lifetime of impurity control components, the idea of protecting the contact surface from erosion and radiation damage with a thin film of liquid metal has been advanced. This flowing, liquid metal film could also be used to remove the high heat fluxes incident on limiter or divertor surfaces, thus eliminating problems with thermal stresses in the components as well. In order to determine the attractiveness and feasibility of such a concept, the heat transfer characteristics of a thin film of liquid metal are examined when the film is exposed to a large, one-sided heat flux incident on the free surface. The method developed yields the temperature at any location in the film and is used to determine, for a given design and space-dependant heat flux, the film velocity required to keep the maximum film temperature below whatever T_max limit is imposed. In addition, the behavior of the film flow at the required velocity is examined in order to determine if such a flow is possible. This analysis is accomplished by using a one-dimensional model of the film height, developed from the basic set of MHD equations, to show the design conditions that allow for a stable film. The analytical method is applied to ITER-type limiter and divertor configurations, resulting in required film velocities (v < 5 m/s for the cases examined) and allowable values of the design parameters (channel size, wall conductivity, and substrate angle) that yield a stable film, capable of removing all incident heat.