Large diameter plastic capsules are necessary in the coming implosion experiments with an upgrade laser system and also in basic experiments of cryogenic targets and injection experiments for reactor technology. For an example, 2-mm-diameter shells with a 200-mm-thick, vacuole-free wall will be used in NIF experiments. The sphericity of the shell must be <3 nm for mode 10 and <0.3 nm for mode 100. To know feasibility of the conventional emulsion method as a technique to fabricate fuel shells for a future laser fusion reactor, we made large polystyrene shells whose diameters were 4 - 7 mm using a three-orifice droplet-generator.

As the results we successfully fabricated required shells with a 30- to 150-mm-thick wall at the production rate of 1 Hz. The sphericity and wall thickness uniformity were >99% and >98%, respectively. It is found that density matching between the oil-phase and the water phase of the emulsions is very important for small shells less than 1.5 mm. However, for large shells, the density matching is not essential to make uniform shells. Appropriate stirring could improve the uniformity.

We assumed that some dynamic centering process exists for large shells and such centering force is provided by deformation of the emulsion. We made two models to analyze the centering force and to improve the thickness uniformity more precisely. One is a pure kinetic model and the other is a surface energy model. In the kinetic model, the interior water globule was assumed to be a solid sphere although the exterior oil surface vibrates in a revolution ellipsoid mode. On the contrary, it is assumed in the surface energy model that the interior water surface moves with the outer oil surface. When the amplitude of the external oil surface is the same, the former force was negligible in large shells.

We are now preparing a rotational drying bed by which emulsions spin around their horizontal axes. By controlling the spin speed, deformation due to gravity will be eliminated and some dynamic deformation will be provided since the emulsion is suspended by two contact points with rollers.

The experimental results will be reported at the conference with models.