Experimental and numerical study of transient condensation of lithium fluoride excited vapors for IFE systems

This paper presents the study of transient cooling and condensation of the non toxic component of flibe, lithium fluoride. The work is part of the effort to provide an experimental feasibility assessment of the application of thick liquid blankets to inertial fusion energy systems. The excited vapors are generated by ablation of about 0.3 grams of a solid sleeve in a high-current electrical discharge, and injected in an expansion chamber under hard-vacuum conditions. The diagnostic system employed includes uniform chamber pressure monitoring, excited gas emission spectroscopy, optical time-of-flight technique and mass spectroscopy of the residual gases. A numerical module has been coupled with the numerical code Tsunami, developed at UCB to simulate gas dynamics in the chamber of IFE systems, to account for condensation at the boundaries of the numerical domain. Results of the application of the code to the geometry and conditions of the experiments are presented. The comparison of the experimental and numerical results allows the analysis of the applicability of the numerical code to simulate the complex mass exchange phenomena encountered in IFE chambers, as well as the validity of the scaled experiments for IFE systems feasibility studies. Lithium fluoride vapors are less volatile than beryllium fluoride, therefore the time resolved measurement of their condensation is a harder challenge for the diagnostic system. Preliminary results of experiments using the prototypical composition of flibe (two thirds lithium fluoride and one third beryllium fluoride in moles) are included in the paper.