Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2005. / Said I. Abdel-Khalik, Committee Chair ; Sheldon M. Jeter, Committee Member ; Minami Yoda, Committee Member. Includes bibliographical references.

One of the most demanding engineering issues in Inertial Fusion Energy (IFE) reactors is the design of a reaction chamber that can withstand the intense photons, neutrons and charged particles due to the fusion event. Rapid pulsed deposition of energy within thin surface layers of the fusion reactor components such as the first wall may cause severe surface erosion due to ablation. One particularly innovative concept for the protection of IFE reactor cavity first walls from the direct energy deposition associated with soft X-rays and target debris is the thin liquid film protection scheme. In this concept, a thin film of molten liquid lead is fed through a silicon carbide first wall to protect it from the incident irradiations. Numerous studies have been reported in the literature on the thermal response of the liquid film to the intermittent photon and ion irradiations, as well as on the fluid dynamics and stability of liquid films on vertical and upward-facing inclined surfaces. However, no investigation has heretofore been reported on the stability of thin liquid films on downward-facing solid surfaces with liquid injection through (i.e. normal to the surface of) the bounding wall. This flow models the injection of molten liquid lead over the upper end cap of the reactor chamber. The hydrodynamics of this flow can be interpreted as a variation of the Rayleigh-Taylor instability due to the effect of the bounding wall which is continuously fed with the heavier fluid. In order to gain additional insight into the thin liquid film protection scheme, experiments have been conducted to investigate the critical issues associated with this concept. To this end, an experimental test facility has been designed and constructed to simulate the hydrodynamics of thin liquid films injected normal to the surface of and through downward-facing flat walls. In this doctoral thesis, the effect of different design parameters (film thickness, liquid injection velocity, liquid properties and inclination angle) on liquid film stability has been examined. The results address the morphology of the film free surface, the frequency of droplet formation and detachment, the size and penetration depth of the detached droplets, and the interface wave number. These experimental data have been used to validate a novel mechanistic numerical code based on a level contour reconstruction front tracking method over a wide range of parameters. The results of this investigation will allow designers of IFE power plants to identify appropriate windows for successful operation of the thin liquid film protection concept for different coolants.

The chamber walls in inertial fusion reactors must be protected from the photons and ions resulting from the target explosions. One way this can be accomplished is through a sacrificial liquid wall composed of either liquid jets or thin liquid films. The x-rays produced by the exploding targets deposit their energy in a thin liquid layer on the wall surface or in the surface of liquid jets arrayed to protect the wall. The partially vaporized liquid film/jet forms a protective cloud that expands toward the incoming ionic debris which arrives shortly (a few s) thereafter. The charged particles deposit their energy in the vapor shield and the unvaporized liquid, thereby leading to further evaporation. Re-condensation of the vapor cloud and radiative cooling of the expanding plasma allow the energy deposited in the liquid to be recovered prior to the next target explosion (100ms). Chamber clearing prior to the next explosion represents a major challenge for all liquid protection systems, inasmuch as any remaining liquid droplets may interfere with beam propagation and/or target injection. Therefore, the primary objective of this research is to experimentally examine the interaction between liquid droplets and low- temperature, low-pressure plasmas under conditions similar to those expected following inertial fusion target explosions and the subsequent expansion. The data obtained in this research will be useful in validating mechanistic chamber-clearing models to assure successful beam propagation and target injection for the subsequent explosion.