Gerald Rivera

Fabrication and Characterization of Targets for Shock Propagation and Radiation Burnthrough Measurements on Be-0.9 AT. % Cu Alloy

Abstract Beryllium-copper alloy (Be0.9%Cu) ICF capsules are being developed for the pursuit of thermonuclear ignition at the National Ignition Facility (NIF). Success of this capsule material requires that its shock propagation and radiation burnthrough characteristics be accurately understood. To this end, experiments are being conducted to measure the shock propagation and radiation burnthrough properties of Be0.9%Cu alloy. These experiments involve measurements on small Be0.9%Cu wedge, step and flat samples. Samples are mounted on 1.6-mm-diameter × 1.2-mm-length hohlraums that are illuminated by the OMEGA laser at the University of Rochester. X-rays produced by the hohlraum drive the sample. A streaked optical pyrometer detects breakout of the shock produced by the X-ray pulse. In this paper we describe synthesis of the alloy material, fabrication and characterization of samples, and assembly of the targets. Samples were produced from Be0.9%Cu alloy that was synthesized by hot isostatic pressing of Be powder and copper flake. Samples were 850 μm diameter disks with varying thickness in the case of wedge and step samples, and uniform thickness in the case of flat samples. Sample thickness varied in the range 10-90 μm. Samples were prepared by precision lathe machining and electric discharge machining. The samples were characterized by a Veeco white light interferometer and an optical thickness measurement device that simultaneously measured the upper and lower surface contours of samples using two confocal laser probes. Several campaigns with these samples have been conducted over the past two years.

Development of Indirectly Driven Shock Tube Targets for Counter-Propagating Shear-Driven Kelvin-Helmholtz Experiments on the National Ignition Facility

Abstract The shear experiments are designed to investigate the transition to turbulence of the Kelvin-Helmholtz instability driven by counter-propagating shear flows. The shear targets for the National Ignition Facility (NIF) shear experiments consist of two hohlraums connected to both ends of a shock tube. The cylindrical shock tube is filled with two hemi-cylindrical CH foams separated by a metal tracer foil. On both ends, a thick gold half-moon–shaped D-plug is placed on opposite halves of the tube to create counter-propagating shock waves. The design is based on a smaller Omega shear target. While the basic NIF design has remained the same, details of the design have undergone several changes over the last 2 years and continue to evolve to improve the quality of the experimental results. Design changes include shock tube designs, tracer foil variations, transitioning to beryllium spool machining, and groove features inside of the tube. Details of how the targets are built including design, machining the parts, target assembly, and metrology are presented, as well as recent target developmental work to meet the needs of future experiments and to improve target assembly efficiency and accuracy.

SPECIALIZED MACHINING TECHNIQUES FOR TARGET AND DIAGNOSTIC FABRICATION

Abstract During the course of machining targets for various experiments, it sometimes becomes necessary to take fixtures or machines that are designed for one function and adapt them to another function. When adapting a machine or fixture is not adequate, it may be necessary to acquire a machine specifically designed to produce the component required. In addition to the above scenarios, the features of a component may dictate that multistep machining processes are necessary to produce the component. This paper discusses the machining of four components where adaptation, specialized machine design, or multistep processes were necessary to produce the components.

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.

Progress in the Production of Materials and Fabrication of NIF Beryllium-Copper Ignition Capsules at Los Alamos National Laboratory

Abstract Work is underway at Los Alamos National Laboratory to fabricate machined-and-bonded target capsules of Be-6 wt% Cu for the National Ignition Facility. Significant progress has been made in producing material with the desired composition, purity, and homogeneity of composition, by arc melting. This material is thermomechanically processed by equal channel angular extrusion, to break down the coarse ascast structure and refine the grain size, to about 20 μm. Machining with diamond tooling results in a significant improvement of the as-machined roughness, that also results in improved bond strengths. Bonding with a sputtered layer of Al can achieve high strengths with a bond 1.2 μm thick, and thinner bonds are being investigated. Laser-drilled holes and fill-tube counterbores produced by electrodischarge machining appear to be feasible, but will require improvements in specimen positioning.

Micromachining of inertial confinement fusion targets

Abstract Many experiments conducted on todays largest inertial confinement fusion drive lasers require target components with sub-millimeter dimensions, precisions of a micron or less and surface finishes measured in nanometers. For metal and plastic, techniques using direct machining with diamond tools have been developed that yield the desired parts. New techniques that will be discussed include the quick-flip locator, a magnetically held kinematic mount that has allowed the direct machining of millimeter-sized beryllium hemishells whose inside and outside surface are concentric to within 0.25 μm, and an electronic version of a tracer lathe which has produced precise azimuthal variations of less than a micron.

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.