Warren P. Steckle

Low-density materials for use in inertial fusion targets

Low-density polymer foams have been an integral part of targets used in inertial confinement fusion (ICF) experiments. Target designs are unique in the ICF program, and targets are made on an individual basis. Costs for these targets are high due to the time required to machine, assemble, and characterize each target. To produce targets in high volume and at low cost, a polymer system is required that is amenable to scale up. High internal phase emulsion (HIPE) polystyrene is a robust system that offers great flexibility in terms of tailoring the density and incorporating metal dopants. Emulsions used to fabricate HIPE foams currently are made in a batch process. With the use of metering pumps for both the water and oil phases, emulsions can be produced in a continuous process. This not only makes these foams potential candidates for direct-drive capsules, but high-Z dopants can be metered in making these foams attractive for hohlraum components in indirect-drive systems. Preparation of HIPE foams are discussed for both direct-drive and indirect-drive systems.

Tritium Inventory of Inertial Fusion Energy Target Fabrication Facilities: Effect of Foam Density and Consideration of Target Yield of Direct Drive Targets

The tritium inventory of direct drive inertial fusion energy (IFE) target filling facilities is examined in the interest of minimizing the tritium inventory. A model is described that has been developed to evaluate the tritium inventory of the target filling process as a function of filling and layering parameters, as well as target design parameters. Previous studies by A. Nobile et al. showed that the temperature and the fill system void fraction have a significant effect on the tritium inventory. The current study uses the model to examine the effect of deuterium-tritium (DT) ice layering time and density of the CH foam in the target on the tritium inventory. The study shows that increasing the foam density and decreasing the DT ice layering time significantly reduce the tritium inventory. Fortunately, one-dimensional target design calculations indicate that the foam density in the direct drive target can be increased to ~200 mg/cm3 without significant degradation of the target yield. Having evaluated and minimized the theoretical tritium inventory, calculations were performed with more realistic batch filling scenarios. The inventories associated with “real” filling scenarios approach the theoretical minimum inventory as the number of batches is increased, resulting in tritium inventories that seem acceptable for future IFE target DT filling facilities.

Feasibility of fluorescence-based imaging of high-energy-density hydrodynamics experiments

Experiments conducted on the LANL Trident two-beam facility show the viability of fluorescence-based imaging as a diagnostic in high-energy-density (HED) hydrodynamics experiments. Passive fluorescence experiments using titanium-pumped scandium-oxide, or iron-pumped manganese-oxide, show that fluorescence emission can be produced at sufficient intensities to be useful. Dynamic experiments, designed to demonstrate particle tracking in time for particle imaging velocimetry (PIV), were marginally successful in that only very large particulates could be definitively observed. However, our results indicate that experiments conducted on facilities offering a greater energy would be less susceptible to the limitations confronted in this study and thus, significantly enhance the prospect of PIV as an effective diagnostic tool in HED experiments.

BEST PRACTICE PROCEDURES FOR MAKING DIRECT DRIVE CYLINDRICAL TARGETS FOR STUDIES OF CONVERGENT HYDRODYNAMICS

Abstract The production of cylindrical targets involves numerous steps. These steps are shared in common with many other types of Inertial Confinement Fusion (ICF) targets but no other single target encompasses such a wide range of fabrication techniques. These targets consist of a large number of individual parts, virtually all fabricated from commercially purchased raw material. As an example, the polystyrene used is synthesized in house from purchased monomer material. This material must be polymerized, purified, characterized and put into solution before it is even first used in the making of a target. Because virtually every manufacturing and assembly process we currently use is involved in the production of these targets, this paper is written as a way documenting the methods used.

A proposed Atlas liner design fabricated for hydrodynamic experiments on Shiva Star

An entirely new cylindrical liner system has been designed and fabricated for use on the Shiva Star capacitor bank. The design incorporates features expected to be applicable to a future power flow channel of the Atlas capacitor bank with the intention of keeping any required liner design modifications to a minimum when the power flow channel at Atlas is available. Four shots were successfully conducted at Shiva Star that continued a series of hydrodynamics physics experiments started on the Los Alamos Pegasus capacitor bank. Departures from the diagnostic suite that had previously been used at Pegasus required new techniques in the fabrication of the experiment insert package.

Fourier Transform Infrared Spectroscopic Analysis of Plastic Capsule Materials Exposed to Deuterium-Tritium (DT) Gas

Abstract Planar samples of varying thicknesses of both CH and CD glow discharge polymer have been measured with Fourier transform infrared (FTIR) spectroscopy before and after exposure to deuterium-tritium (DT) gas at elevated temperature and pressure. Planar samples of polyimide films made from both hydrogenated and deuterated precursors have also been examined by FTIR before and after DT exposure. The post-exposure FTIR spectra demonstrated no measurable exchange of hydrogen with deuterium or tritium for either polymer. Evidence for oxidation of the glow discharge polymer due to atmospheric oxygen was the only chemical change indicated by the FTIR data.

Machining damaged surface hydrodynamic (DSH) spall target assemblies used in high energy compression physics experiments

Summary form only given. Targets were designed and manufactured to simulate a damaged surface in a series of high energy density (HED) experiments. The simulated damaged surface was a zero strength epoxy powder of nominally 1 mum and 5 mum diameter tungsten particles. This design feature introduced a number of manufacturing issues such as two precision grooves in the target wall and glide planes (upper and lower), alignment slots in the upper glide plane, developing the zero strength tungsten powder surface, a cryogenic interference fit, and a precision surface finish. Custom tooling, fixturing, and unconventional machining methods were utilized to mitigate manufacturing issues and are described in the poster. The targets were fielded at the Nevada Test Site (NTS) on the Atlas pulse power machine.

Recent Developments in Fabrication of Direct Drive Cylinder Targets for Hydrodynamics Experiments at the OMEGA Laser

Abstract Experimental campaigns are being conducted at the 60 beam OMEGA laser at the University of Rochester’s Laboratory for Laser Energetics to acquire data to validate hydrodynamic models in the high energy-density regime. This paper describes targets that have been developed and constructed for these experimental campaigns. Targets are 860 μm inner diameter by 2.2 mm length cylinders with 70 μm thick polymer ablator. On the ablator inner surface and located halfway along the axis of the cylinder is a 500 μm wide Al marker band. Band thicknesses in the range 8-16 microns are used. CH foam with densities in the range 30-90 mg/cc fills the inside of the cylinder. While these targets have been fabricated for years, several new improvements and features have recently been developed. Improvements include the use of epoxy instead of polystyrene for the ablator, and the use of electrodeposited Al for the marker band. A critical feature of the target is the surface feature that is placed on the marker band. Experiments are aimed at understanding the hydrodynamic behavior of imploding cylinders as a function of this surface feature. Recent development work has focused on production of engineered surface features on the target marker band. Using a fast tool servo on a diamond turning lathe, a wide range of specified surface features have been produced. This paper will address improvements to the cylinder targets as well as current development efforts.