Joyce E. Moore

Microcellular foams: phase behaviour of poly(4-methyl-1-pentene) in diisopropylbenzene

Abstract Microcellular foams are an important component of Inertially Confined Fusion (ICF) targets. The spatial distribution of the material is critical as the target implodes. In an effort to improve the spatial uniformity, we have explored the phase separation behaviour of poly(4-methyl-1-pentene) solutions with diisopropylbenzene solvent. The cloud-point phase-separation diagram from pure solvent to pure polymer is discussed. Microstructures of the various density foams and the need for a three-dimensional phase diagram are presented.

Effect of several dual solvents on the phase separation of poly(4-methyl-1-pentene)

Abstract Phase separation of isotactic poly(4-methyl-1-pentene) (PMP) from various solvents gives polymer masses which can be converted into foams that vary from crumbly powders to well-connected, strong, flexible solids. The composition of the solvent is an important parameter in determining the nature of the separated polymer phase. The influence of solvent (or non-solvent) on the temperature and character of the phase separation event and on the resulting foam structure is addressed in this paper. Thus differing ratios of two poor solvents for PMP, bibenzyl and paraffin, were found to give variable foam structures and surprising phase behaviour. Thermochromism is sometimes observed as the polymer separates.

Coating techniques used in target fabrication

Abstract A review of coating techniques used to fabricate targets and experimental components is presented. Coating techniques include physical vapor deposition, chemical vapor deposition, electroplating and dip coating. In all cases the substrate or mandrel material is removed from the coating to result in the final part.

Machining sub-millimeter beryllium and aluminum components of laser targets

We show the development of tooling, miniature boring tools, and the machining steps required in the machining operations for sub-millimeter beryllium and aluminum components of laser targets. The targets were built for the Helen Laser at AWE, Aldermaston in the UK and were designed to measure the response of aluminum to the passage of mega-bar shock waves. 1 refs., 8 figs.

Targets for laser-driven opacity measurements

Abstract Special laser targets have been designed and fabricated which allow the opacity of materials to be experimentally determined at elevated temperatures ( kT ≤ 200 eV). A general description of the technique is presented, as well as the fabrication steps necessary to produce the targets. A uniform high temperature environment is provided by the use of small millimeter-sized hohlraums driven by the Nova laser at Lawrence Livermore National Laboratory. The material sample is placed within the hohlraum and is further illuminated by the X-rays produced by one or two of the Nova beams incident on a second material known as a back lighter. Thus far, silver and niobium opacity samples have been used, and each has required a different fabrication technique.

Preparation of microcellular foam in cylindrical gold targets

The preparation of microcellular foam in submillimeter cylindrical gold targets is described. The gold cylinders were fabricated by electroplating gold onto a silicon bronze mandrel and leaching the mandrel with concentrated nitric acid. After several rinsing and cleaning steps, the cylinders were filled with a solution containing trimethylolpropanetriacrylate (TMPTA). Low density, microcellular polymeric foam was prepared by in situ photopolymerization of the TMPTA solution. Foam preparation was extremely sensitive to metal ion contaminants. In particular, copper ions left behind from ineffective leaching of the silicon bronze mandrels inhibit polymerization and must be removed in order to obtain uniform, nonshrinking foams. A procedure for the effective leaching of the mandrels is described. In addition, a study on the effects of potential contaminants and polymerization inhibitors on TMPTA photopolymerization is presented.

High‐Z elements in laser fusion targets

Recent laser fusion experiments conducted by Los Alamos physicists have required the use of high‐Z elements in atypical applications. Gold, a commonly used element, has been deposited in low‐density smoke form onto plastic and glass spheres. Thorium and uranium have been requested as x‐ray backlighter materials, and wires etched to <10 μm have been produced for this purpose. Uranium has also been vapor deposited onto spheres and 7–10 μm fibers with varying degrees of success.

Fabrication of the 3.2 gram Pegasus-II aluminum liner and load components of the Liner Ejecta Experiment

Fabrication of the 3.2 gram Pegasus-II 1100 series aluminum liner is described. This liner is driven by nominally 5 MA from the Pegasus-II two-stage Marx bank charged to approximately 35 kV. The liner will accelerate symmetrically to a final velocity of 3 mm//spl mu/s while it remains in contact with an annular glide plane surface at each electrode for a radial distance of 7.5 mm. At this drive level, up to 300 kbar shocks are expected when the solid density liner wall collides with the surface of a cylindrical liner experiment assembly mounted on axis within the liner bore. Components of the Los Alamos Liner Ejecta Experiment are described as one example of a Pegasus-II liner experiment.

Gas-filled hohlraum fabrication

Los Alamos National Laboratory (LANL) researchers have fabricated and fielded gas-filled hohlraums at the Lawrence Livermore National Laboratory (LLNL) Nova laser. Fill pressures of 1--5 atmospheres have been typical. We describe the production of the parts, their assembly and fielding. Emphasis is placed on the production of gas-tight polyimide windows and the fielding apparatus and procedure.