Estimates of the effect of a plasma momentum flux on the free surface of a thin film of liquid metal

The use of a thin film of liquid metal (LM) to protect a divertor surface requires that the LM film be able to withstand the flux of momentum carried by the energetic plasma exhaust flow. This momentum flux was estimated from edge modeling results of an ITER conceptual design activity (CDA) type divertor, and was found to be comparable with the hydrostatic pressure of a typical LM film of the order of millimeters in height. A two-dimensional, free boundary fluid code, RIPPLE, was modified to account for this flux and used to give an initial estimate of the seriousness of this effect. Lithium films are dramatically affected, to such a degree that their use in an LM divertor is seriously questioned. Gallium films withstand the momentum flux much better, with speeds of around 1 m s−1 giving adequate performance in a realistic CDA divertor momentum flux profile. The inclusion of magnetohydrodynamic forces, not present in this initial estimation, is required to describe fully the LM film response.