Deanna Capelli

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.

Design and Fabrication of Opacity Targets for the National Ignition Facility

Abstract Accurate models for opacity of partially ionized atoms are important for modeling and understanding stellar interiors and other high-energy-density phenomena such as inertial confinement fusion. Lawrence Livermore National Laboratory is leading a multilaboratory effort to conduct experiments on the National Ignition Facility (NIF) to try to reproduce recent opacity tests at the Sandia National Laboratory Z-facility. Since 2015, the NIF effort has evolved several hohlraum designs that consist of multiple pieces joined together. The target also has three components attached to the main stalk over a long distance with high tolerances that have resulted in several design iterations. The target has made use of rapid prototyped features to attach a capsule and collimator under the hohlraum while avoiding interference with the beams. This paper discusses the evolution of the hohlraum and overall target design and the challenges involved with fabricating and assembling these targets.

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.

The Laser-Driven X-ray Big Area Backlighter (BABL): Design, Optimization, and Evolution

The Big Area BackLigher (BABL) has been developed for large area laser-driven x-ray backlighting on the National Ignition Facility (NIF), which can be used for general High Energy Density (HED) experiments. The BABL has been optimized via hydrodynamic simulations to produce laser-to-x-ray conversion efficiencies of up to nearly 5%. Four BABL foil materials, Zn, Fe, V, and Cu, have been used for He-α x ray production.

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.