Design of an experimental test stand for the study of liquid lithium film stability

The benefits of having the walls of fusion devices partially or even totally covered with lithium are widely recognized, as evidenced by the growing number of experimental devices with programs devoted to lithium wall conditioning. There are, however, many outstanding questions regarding technology aspects of lithium handling when placed in a tokamak experiment. The present work describes the preliminary design activities of a test facility devoted to the study of liquid lithium, in particular film stability when thermal gradients are present on downward-facing surfaces. The capability of studying the effect of thermodynamic compatibility between the liquid and the substrate will also be possible in this facility. Two mechanisms for film formation are being considered: condensed films formed from evaporative material, and creeping films formed by flow of metal from a liquid reservoir. Results from finite element modeling for stagnant and flowing films coupled with thermal effects are presented; these simulations will be benchmarked against experimental observations once the facility is constructed. The facility will also have the capability of studying MHD effects, since it will be attached to the TPM-1U tokamak, a small machine currently under construction. The expected TPM-1U toroidal field is expected to be on the order of 0.3 T. The coupling of the liquid lithium test stand to the small tokamak will allow the study of liquid lithium flows subjected to full toroidal fields, with no end effects as in previous experiments.