University of Rochester

Harry W Deckman

Dennis G Peiffer

Gerald M Halpern

Irving S Goldstein

John G Dunsmuir

Franklin D Kalk

Extremely small, three-dimensional articles, such as fusion targets having glass shells (20 to 500 microns in diameter) are coated with alternate layers of colloidal materials. This is accomplished by depositing particles of opposite charge from colloidal suspensions (sols). Articles to be coated are suspended within a drop held in the open end of a closed capillary tube, and colloidal particles are deposited by dipping the capillary into the sols. Alternate monolayers of the particles adhere to the surface of the article. Multilayer coatings are built up by repeated alternate deposition of the monolayers from the sols. Between each deposition, the layers are rinsed with water and the water removed by dipping the capillary tube into a bath of water and then into a bath containing a water displacing agent such as ethanol or dimethyl sulfoxide.

Colloidal coating for small three dimensional articles, and particularly

Identical half-section shells of microscopic size, such as hemispherical shells from which spherical laser fusion targets can be made are capable of mass production by micro fabrication molding techniques. A body (preferably a hollow glass microsphere which is called a glass microballoon) provides a pattern for the hemispherical shells, and is used to produce an original mold section. One or more master molds are formed from this original mold section by replication. Many identical replica molds are made by casting soluble material onto the master mold and removing them therefrom. The replica molds are coated with one or more layers which will form the hemispherical shell wall. The material coating the flat background around the hemispherical cavity is referred to as the flange and is removed to form free standing shells. In order to remove the flange material, the coated replica molds are overcoated with a soluble material which is etched away to the level of the flange. The remaining soluble material acts as a mask for the shell material when the flange material is etched away. The replica mold and overcoating body remain as a protective mask and are dissolved away to release the identical shell sections. These sections can be assembled to provide closed shells. Overlapping lips can be formed during flange removal so as to facilitate the assembly of the sections into the closed shells.

Micro fabrication molding process

Hollow shell laser fusion targets, such as glass microballoons, are filled with gases of the type which do not permeate through the wall of the balloon. A hole is laser-drilled in the balloon, a plug is placed over the hole and gas is introduced into the balloon through the loosely plugged hole. Thereafter the plug is melted to form a seal over the hole, entrapping the gas within the target. The plug is, for example, a polymer such as highly crystalline polystyrene, or glass.

Method for filling hollow shells with gas for use as laser fusion targets

In order to assay the tritium fuel content in laser fusion targets and/or to measure the pressurization of laser fusion targets of the type which use deuterium and tritium (DT) gas mixtures, without destroying the targets, the flux of beta particles which emerges from the target is measured with the aid of a gas flow proportional counter. The count rates are related to the tritium content and the pressurization. The tritium content in terms of the mass of the tritium in the target can be derived from the counting rate.

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Fanwood, NJ, United States of America

Harry W Deckman