Modeling of Microencapsulated Polymer Shell Solidification

Abstract

A finite element transport model has been developed and implemented to complement experimental efforts to improve the quality of ICF target shells produced via controlled-mass microencapsulation. The model provides an efficient means to explore the effect of processing variables on the dynamics of shell dimensions, concentricity, and phase behavior. Comparisons with experiments showed that the model successfully predicts the evolution of wall thinning and core/wall density differences. The model was used to efficiently explore and identify initial wall compositions and processing temperatures which resulted in concentricity improvements from 65 to 99%. The evolution of trace amounts of water entering into the shell wall was also tracked in the simulations. Comparisons with phase envelope estimations from modified UNIFAP calculations suggest that the water content trajectory approaches the two-phase region where vacuole formation via microphase separation may occur.

Fabrication of special inertial confinement fusion targets using a depolymerizable mandrel technique

“…[3][4][5][6] The microshell is next overcoated with 50 m or more of plasma polymer ͑CH͒ 7,8 to provide a thick ablator layer which absorbs the laser energy and drives the compression of the fuel capsule. There are two common methods for making microshells.…”

“…6 With the depolymerizing mandrel technique, we form the layer that becomes the shell by vapor deposition; wall uniformity is consequently good. First, it represents a route to large capsules with uniform wall thickness and excellent sphericity.…”