Numerical and Experimental Analysis of a Fluidized Bed for Ife Target Layering

A fluidized bed is being studied as a very promising method for mass production of IFE targets. Large beds could be filled with many targets to provide large-scale production, while a near-isothermal environment could be maintained in principle around each target (as required for smooth layering to meet the physics requirements on the ice characteristics) through the random movement and spin of individual targets within a precisely controlled gas stream. Concerns exist, however, including the effect of unbalanced spheres on the bed behavior and ultimately on the target thermal environment, as well as the possible damage of the target surface (in particular the thin high-Z coating). This effort includes developing a numerical fluidized bed model and conducting laboratory-scale companion experiments to help understand the cryogenic fluidized bed behavior. Key challenges in developing the model include the relative size of the spherical targets (~4.0 mm) compared to the size of the prototypic fluidized bed container (~26 mm in diameter), which is much larger than those found in conventional fluidized bed models and which calls for a different modeling approach. In addition, the behavior of unbalanced targets, which results from the initial D-T filling and freezing in the target production process, needs to be accounted for. This paper summarizes the development of this model, including the validation performed by comparing the model results to controlled lab-scale experiments. The goal is to use the model for parametric analysis to help determine the most promising state of operation to deliver large quantities of uniformly layered target shells. This will provide key pre-operational input to the prototypical experimental set-up, which is currently being built and which includes a high-pressure deuterium filling station in addition to the cryogenic fluidized bed operating at temperatures around 18 K.