J.J. Bartos

RANCHERO explosive pulsed power experiments

The authors are developing the RANCHERO high explosive pulsed power (HEPP) system to power cylindrically imploding solid-density liners for hydrodynamics experiments. Their near-term goal is to conduct experiments in the regime pertinent to the Atlas capacitor bank. That is, they will attempt to implode liners of /spl sim/50 g mass at velocities approaching 15 km/sec. The basic building block of the HEPP system is a coaxial generator with a 304.8 mm diameter stator, and an initial armature diameter of 152 mm. The armature is expanded by a high explosive (HE) charge detonated simultaneously along its axis. The authors have reported a variety of experiments conducted with generator modules 43 cm long and have presented an initial design for hydrodynamic liner experiments. In this paper, they give a synopsis of their first system test, and a status report on the development of a generator module that is 1.4 m long.

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.

Hohlraum manufacture for inertial confinement fusion

Hohlraums are an integral part of indirect drive targets for Inertial Confinement Fusion (ICF) research. Hohlraums are made by an electroforming process that combines elements of micromachining and coating technology. The authors describe how these target elements are made and extensions of the method that allow fabrication of other, more complex target components.

New residual stress mapping tool applied to Atlas current joint design

A redesigned cylindrical liner system has been implemented for use on the Atlas capacitor bank. This new design dramatically changes how the liner, glide planes and current joints of the system are formed. The previous design relied on interference of the liner with the glide plane by thermal shrink fit using liquid nitrogen coolant to form current joints. The new design achieves the required fit by mechanically distorting soft metals with a swaged joint. In this paper, we present the results of the first application of a new residual stress mapping technique, the contour method, to the design and fabrication process of the Atlas upper current joint. One of the strengths of the contour method is that it provides a full cross-sectional map of the residual-stress component normal to the cross section. The results showed significant stresses in the stainless steel glide plane with expected maximum compression near the joint and stresses in the aluminum part liner and return current conductor that corresponds well with measured form distortions.

Design and operation of high energy liner implosions at 16 MA for studies of converging shocks

Electromagnetically-driven implosion of solid-density, cylindrical liners can launch shocks with excellent precision at impact speeds exceeding 5 km/s. We discuss the design and operation of liner implosions driven at peak currents of 16MA, using the Shiva Star capacitor bank at the Air Force Research Laboratory. Liners of 1100 aluminum, with initial length, radius and thickness of 4 cm, 5 cm and 1 mm, respectively, implode under the action of an axial current, rising in 8 /spl mu/s. Fields on conductor surfaces exceed 0.6 MG. The inner surface of the liner achieves a speed of 6.25 km/s when it impacts a concentric target cylinder of tin at a radius of 2 cm. Magnetic probes and radially-aligned X-radiography follow the motion of the liner and its impact on the tin cylinder. This cylinder holds a solid cylinder of acrylic of 1.5 cm radius in which the motion of a converging shock is followed by optical shadowgraphy and axially-aligned, X-radiography. Design issues that were successfully addressed include: Pulsed Power - current joints at high magnetic fields in the vicinity of the liner and glide-plane/electrodes, where magnetic pressures quickly exceed values for mechanical pre-stress, requiring dynamic solutions; surface temperature enhancements at changes in current direction; possibility of electrical breakdown at connection of liner cassette insulator to bank insulation; need for magnetic inhibition of breakdown (MIB) between liner surface and insulator; Liner Physics - angle needed to maintain current contact between liner and glide-plane/electrode without jetting or buckling; nonlinear magnetic diffusion into liner and associated melting; Diagnostics X-radiography through cassette insulator and outer conductor without shrapnel damage to film.

Liquid butane filled load for a liner driven Pegasus experiment

A hydrogen rich, low density liquid, contained within the internal volume of a cylindrical liner, was requested of the Polymers and Coatings Group (MST-7) of the Los Alamos Materials Science Division for one of the last liner driven experiments conducted on the Los Alamos Pegasus facility. The experiment was a continuation of the Raleigh-Taylor hydrodynamics series of experiments and associated liners that have been described previously.

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.

Loads for pulsed power cylindrical implosion experiments

Pulse power can be used to generate high energy density conditions in convergent hollow cylindrical geometry through the use of appropriate electrode configuration and cylindrical loads. Cylindrically symmetric experiments are conducted with the Pegasus-II inductive store, capacitor energized pulse power facility at Los Alamos using both precision machined cylindrical liner loads and low mass vapor deposited cylindrical foil loads. The liner experiments investigate solid density hydrodynamic topics. Foil loads vaporize from Joule heating to generate an imploding cylindrical plasma which can be used to simulate some fluxes associated with fusion energy processes. Similar experiments are conducted with {open_quotes}Procyon{close_quotes} inductive store pulse power assemblies energized by explosively driven magnetic flux compression.