Randall B. Randolph

Process Development and Micro-Machining of MARBLE Foam-Cored Rexolite Hemi-Shell Ablator Capsules

Abstract Machined CH hemi-shell ablator capsules have been successfully produced by the MST-7 Target Fabrication Team at Los Alamos National Laboratory. Process development and micro-machining techniques have been developed to produce capsules for both the Omega and National Ignition Facility (NIF) campaigns. These capsules are gas filled up to 10 atm and consist of a machined plastic hemi-shell outer layer that accommodates various specially engineered low-density polystyrene foam cores. Machining and assembly of the two-part, step-jointed plastic hemi-shell outer layer required development of new techniques, processes, and tooling while still meeting very aggressive shot schedules for both campaigns. Problems encountered and process improvements will be discussed that describe this very unique, complex capsule design approach through the first Omega proof-of-concept version to the larger NIF version.

Utilizing Conventional Machining Tools with Customized Machining Techniques to Manufacture Multifaceted Targets

Abstract Three recent experimental campaigns at Los Alamos National Laboratory have required unique application of traditional machining techniques to manufacture the components. For pRad experiments at Los Alamos Neutron Science Center (LANCE), unique planar targets with varying profiles required unique fixturing: a custom programming software to create concentric rings with a 2-deg taper that had five different sine waves machined across the face. Also, experiments using P8 modulated capsules for Asymmetric Burn Experiment (ABEX) experiments at Omega made use of a water-soluble ultraviolet-curable glue, which was used for holding and locating purposes during machining operations to produce an indicating datum, as well as a custom fixturing system, which allowed the ability to apply the impression gum from behind. Finally, for the milling of a 125-μm-thick silica aerogel for dense-plasma equation-of-state experiments, we used an ultraprecision milling machine with a high-speed spindle and precise positional accuracy that permits micrometer depth of cuts at higher feed rates, which allowed for a reduction in machining time.

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.

Dry-Machining of Aerogel Foams, CH Foams, and Specially Engineered Foams Using Turn-Milling Techniques

Abstract A new method has been developed to dry-machine foams. Most of these foams are at the lower end of what is considered machineable because of their density or foam composition. Excluding aerogel foams, the foams traditionally required a wax-fill process before surviving any machining forces. This new dry-machining method uses a technique called turn-milling and replaces the old wax-fill method that added several weeks to the fabrication schedule and uncertainty in the quality of the final part. The new method utilizes a computer numerical control gang-tool–style lathe that is set up with electric live-tooling spindles. The foams are dry-machined with the lathe main spindle turning in the opposite direction of the live-tooling spindle. This turn-milling technique reduces tool pressure and can accommodate heavier roughing cuts that produce much faster cycle times. With this new dry-machining method we are able to machine the entire foam target component in one operation, eliminating the need for another machining operation for finishing the backside.

Progress Toward Fabrication of Machined Metal Shells for the First Double-Shell Implosions at the National Ignition Facility

Abstract The double-shell platform fielded at the National Ignition Facility requires developments in new machining techniques and robotic assembly stations to meet the experimental specifications. Current double-shell target designs use a dense high-Z inner shell, a foam cushion, and a low-Z outer shell. The design requires that the inner shell be gas filled using a fill tube. This tube impacts the entire machining and assembly design. Other intermediate physics designs have to be fielded to answer physics questions and advance the technology to be able to fabricate the full point design in the near future. One of these intermediate designs is a mid-Z imaging design. The methods of designing, fabricating, and characterizing each of the major components of an imaging double shell are discussed with an emphasis on the fabrication of the machined outer metal shell.

Target Fabrication of Opacity Experiments on Z for Weapons Science Applications

Abstract Opacity data are very important in high energy density physics experiments. Recent targets of alternating layers of either Al2Te3 or Mg/Sn with a CH tamper have been made for obtaining these data. These targets are geometrically simple in the half-moon configuration of the metal compound coating to the pure CH tamper but require stringent procedural requirements to fabricate to the purity requirements. These specific targets require mass ratios of elements that proved to be difficult to obtain while also having the requirement of being pinhole-free and oxygen-free.

Improvements in ICF target fabrication through high precision assembly and nondestructive characterization

Current ICF and HED targets are fielded on Omega, Z, and Trident; future campaigns will also be fielded on NIF. NIF will field less than 2 shots per day. With such few experiments, target fabrication and alignment accuracy, enhanced metrology and advanced component machining will be even more important. Future target designs are also becoming more complex and more stringent in terms of both manufacturing accuracy and precision. Several steps have been taken to improve the fabrication and characterization of targets, such as instituting an automated assembly station with 3 μm tolerances, utilizing non-destructive characterization tools for rapid component metrology and target assembly, and advancing machining capabilities. Recapitalization of target fabrication infrastructure is continuous.