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Atlas is a pulsed power machine designed for hydrodynamic experiments for the Los Alamos High Energy Density Physics Experimental program. It is presently under construction and should be operational in late 2000. Atlas will store 23 MJ at an erected voltage of 240 kV. This will produce a current of 30 MA into a static load and as much as 32 MA into a dynamic load. The current pulse will have a rise time of {approximately}5{micro}s and will produce a magnetic field driving the impactor liner of several hundred Tesla at the target radius of one to two centimeters. The collision can produce shock pressures of {approximately}15 megabars. Design of the pulsed power system will be presented along with data obtained from the Atlas prototype Marx module.

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The multi-megabar shock driver development is a series of experiments in support of the Los Alamos High Energy Density Physics Experimental Program. Its purpose is to develop techniques to impact a uniform, stable, composite liner upon a high Z target to produce a multi-megabar shock for EOS studies. To date, experiments have been done on the Pegasus II capacitor bank with a current of {approximately}12MA driving the impactor liner. The driving field is {approximately}200 T at the target radius of 1cm. Data will be presented on the impactor liner. The driving field is {approximately}200 T at the target radius of 1 cm. Data will be presented on the stability and uniformity of the impactor liner when it impacts the target cylinder. Three experiments have been done with emphasis on liner development. Shock pressures greater than a megabar have been done with emphasis on liner development. Shock pressures greater than a megabar have been produced with an Al target cylinder. A Pt target cylinder should produce shock pressures in th e 5-megabar range.

It is widely acknowledged that Mure neutron-detection technologies will need to offer increased performance at lower cost. One clear route toward these goals is rapid and direct detection of fast neutrons prior to moderation. This report describes progress to date in an effort to achieve such neutron detection via proton recoil within plastic scintillator. Since recording proton-recoil events is of little practical use without a means to discriminate effectively against gamma-ray interactions, the present effort is concentrated on demonstrating a method that distinguishes between pulse types. The proposed method exploits the substantial difference in the speed of fission neutrons and gamma-ray photons. Should this effort ultimately prove successful, the resulting. technology would make a valuable contribution toward meeting the neutron-detection needs of the next century. This report describes the detailed investigations that have been part of Pacific Northwest National Laborato@s efforts to demonstrate direct fast-neutron detection in the laboratory. Our initial approach used a single, solid piece of scintillator along with the electronics needed for pulse-type differentiation. Work to date has led to the conclusion that faster scintillator and/or faster electronics will be necessary before satisfactory gamma-ray discrimination is achieved with this approach. Acquisition and testing of both faster scintillator …

Los Alamos flux compression activities are surveyed, mainly through references in view of space limitations. However, two plasma physics programs done with Sandia National Laboratory are discussed in more detail.

Often helical flux-compressor generator (FCG) design codes are essentially circuit codes which utilize known equations for parameterizing circuit elements such as armature and stator inductance. The authors present an analytical model that is based more on first principals. The stator inductance is calculated using a definition of inductance in terms of the magnetic vector-potential. The calculation accounts for winding-pitch, bifurcations, and works for any ratio of length to diameter. The currents on the armature are calculated self-consistently and are not assumed to simply 'mirror' the stator currents. Resistive losses and magnetic diffusion losses are calculated less rigorously but they are working on better methods. Details of the model and comparison with experiment will be presented.

At Los Alamos, the authors have primarily applied Explosively Formed Fuse (EFF) techniques to high current systems. In these systems, the EFF has interrupted currents from 19 to 25 MA, thus diverting the current to low inductance loads. The magnitude of transferred current is determined by the ratio of storage inductance to load inductance, and with dynamic loads, the current has ranged from 12 to 20 MA. In a system with 18 MJ stored energy, the switch operates at a power up to 6 TW. The authors are now investigating the use of the EFF technique to apply high voltages to high impedance loads in systems that are more compact. In these systems, they are exploring circuits with EFF lengths from 43 to 100 cm, which have storage inductances large enough to apply 300 to 500 kV across high impedance loads. Experimental results and design considerations are presented. Using cylindrical EFF switches of 10 cm diameter and 43 cm length, currents of approximately 3 MA were interrupted producing {approximately}200 kV. This indicate s the switch had an effective resistance of {approximately}100 m{Omega} where 150--200 m{Omega} was expected. To understand the lower performance, several parameters were studied, including: electrical conduction through …

The authors have developed a system for driving hydrodynamic liners at currents approaching 30 MA. Their 43 cm module will deliver currents of interest, and when fully developed, the 1.4 m module will allow similar currents with more total system inductance. With these systems they can perform interesting physics experiments and support the Atlas development effort.

Imploding, cylindrical liners provide a unique, shockless means of simultaneously accessing high strain and high-strain-rate for measurement of strength of materials in plastic flow. The radial convergence in the liner geometry results in the liner thickening as the circumference becomes smaller. Strains of up to {approximately}1.25 and strain rates of up to {approximately}10{sup 6} sec{sup -1} can be readily achieved in a material sample placed inside of an aluminum driver liner, using the Pegasus II capacitor bank. This provides yield strength data at conditions where none presently exists. The heating from work done against the yield strength is measured with multichannel pyrometry from infrared radiation emitted by the material sample. The temperature data as a function of liner position are unfolded to give the yield strength along the strain, strain-rate trajectory. Proper design of the liner and sample configuration ensures that the current diffused into the sample adds negligible heating. An important issue, in this type of temperature measurement, is shielding of the pickup optics from other sources of radiation. At strains greater than those achievable on Pegasus, e.g. the LANL Atlas facility, some materials may be heated all the way to melt by this process. Recent data on 6061-T6 …

LANL and VNIIEF are performing a set of joint experiments to explore the conductivity and possible metalization of argon and krypton compressed to up to five times normal solid density. The experiments use a magnetic field of several megagauss, generated by a Russian MC1 generator, to compress a metallic tube containing solidified argon or krypton. A probe in the center of the tube measures the electrical conductivity to the walls, and a 70-MeV betatron serves as an x-ray source for three radiographic measurements of the compression. Several of these experiments for argon compressed to around 4 to 5 times solid density indicate a conductivity in the range of 10 to 100 {Omega}{sup -1}cm{sup -1}, well below that of a metal. For krypton preliminary results show a conductivity of order 1000 or more, indicating likely metalization of the compressed sample.

A series of experiments to compare imploding liner performance with magneto-hydrodynamic (MHD) modeling has been performed at the Los Alamos National Laboratory Pegasus II pulse power machine. Liner instability growth originating from initial perturbations machined into the liner has been observed with high resolution. Three major diagnostics were used: radiography, Velocity Interferometer for a Surface of Any Reflector (VISAR), and fiber optic impact pins. For radiography, three flash x-ray units were mounted radially to observe liner shape at three different times during the implosion. Liner velocity was measured continuously with the VISAR for the entire distance traveled in two experiments. Optical impact pins provide a high-resolution measure of liner symmetry and shape near the end of travel. Liner performance has compared well with predictions.

A technique is developed for linking the methods of discrete dislocation dynamics simulation and finite element to treat elasto-plasticity problems. The overall formulation views the plastically deforming crystal as an elastic crystal with continuously changing dislocation microstructure which is tracked by the numerical dynamics simulation. The FEM code needed in this regard is based on linear elasticity only. This formulation presented here is focused on a continuous updating of the outer shape of the crystal, for possible regeneration of the FEM mesh, and adjustment of the surface geometry, in particular the surface normal. The method is expected to be potentially applicable to the nano- indentation experiments, where the zone around the indenter-crystal contact undergoes significant permanent deformation, the rigorous determination of which is very important to the calculation of the indentation print area and in turn, the surface hardness. Furthermore, the technique is expected to account for the plastic history of the surface displacement under the indenter. Other potential applications are mentioned in the text.

A non-destructive, one megagauss magnet is now being designed in cooperation between Los Alamos and the National High Magnetic Field Laboratory (NHMFL) through joint funding by the US Department of Energy and the US NSF. The design combines two types of pulsed magnet now in use at the NHMFL: a capacitor-driven 'insert' magnet with a total pulse width of order 10 ms and a much larger 'outsert' magnet with a total pulse width of order 2 seconds that is driven by a controlled power source. The insert and outsert produce approximately 1/2 megagauss each. Although the design uses CuAg as the principal conductor further design efforts and materials development are exploring CuNb and stainless steel-clad copper as possible future alternatives. A crucial innovation was to employ wound steel strip (sheet) as a reinforcement in both insert and outsert coils. This gives extra strength due to the higher degree of cold-work possible in strip materials. For this leading edge magnet a key role is played by materials development. A major component, the 7 module 560 MVA controlled dc power supply required for the outsert, has been installed and commissioned.

In the concept known as Magnetized Target Fusion (MTF) in the United States and Magnitnoye Obzhatiye (MAGO) in Russia, a preheated and magnetized target plasma is hydrodynamically compressed to fusion conditions. Because the magnetic field suppresses losses by electron thermal conduction in the fuel during the target implosion heating process, the compression may be over a much longer time scale than in traditional inertial confinement fusion. Hence ''liner-on-plasma'' compressions, magnetically driven using relatively inexpensive electrical pulsed power, may be practical. One candidate target plasma known as ''MAGO'' was originated in Russia and is now being jointly developed by the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) and Los Alamos National Laboratory (LANL). Other possible target plasmas now under investigation at LANL include wall-supported deuterium-fiber-initiated Z-pinches and compact toroids. Detailed computational modeling is being done of such target plasmas. In addition, liner-on-plasma compressions of such target plasmas to fusion conditions are being computationally modeled, and experimental and computational investigation of liner implosions suitable for MTF is continuing. Results will be presented.

The authors report results of one-and-two-dimensional MHD simulations of an imploding heavy liner in Z-pinch geometry. The driving current has a pulse shape and peak current characteristic of the Atlas pulsed-power facility being constructed at Los Alamos National Laboratory. One-dimensional simulations of heavy composite liners driven by 30 MA currents can achieve velocities on the order of 14 km/sec. Used to impact a tungsten target, the liner produces shock pressures of approximately fourteen megabars. The first 2-D simulations of imploding liners driven at Atlas current parameters are also described. These simulations have focused on the interaction of the liner with the glide planes, and the effect of realistic surface perturbations on the dynamics of the pinch. It is found that the former interaction does not seriously affect the inner liner surface. Results from the second problem indicate that a surface perturbation having amplitude as small as 0.2 {micro}m can have a significant effect on the implosion dynamics.

Ranchero is an explosively driven magnetic flux-compression generator that has been developed, over the last four years, as a versatile power source for high energy density physics experiments. It is coaxial, and comprises a 15 cm-diameter armature and a 30-cm stator, each aluminum. The length may be varied to suit the demands of each experiment; thus far, lengths of 0.43 m and 1.4 m have been used. The stator is filled and driven by a high performance cast explosive, and the ultimate performance of the device is limited by the smoothness of the armature expansion. The armature explosive is initiated on axis by PETN hemispheres, spaced at intervals of about 18 mm and 24.5 mm; each is simultaneously detonated by a slapper detonator system. Calculations of armature expansion predicted ripples less than 0.2 mm, and this was confirmed in early experiments. Yet, ripples approaching tens of millimeters were observed in some more recent experiments. The authors discuss the possible origins of the se large ripples, and the methods the authors have used to correct them.

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Report on reactor sharing program at the University of Arizona.

High explosive pulsed power (HEPP) is a specialized subset among pulsed power endeavors which takes advantage of the very high energy density available in both magnetic fields and high explosives (HE). To introduce basic concepts, the author divides HEPP components into generators (magnetic field (B) or current (I)) and switches. Magnetic field and current generators start with magnetic field trapped in a conducting volume. Magnetic flux can be expressed as either LI or BA, where L and A (inductance and cross sectional area) are both geometry dependent circuit properties. In a purely inductive circuit, flux is conserved, so L{sub 1}I{sub 1}=L{sub 2}I{sub 2} or B{sub 1}A{sub 1}=B{sub 2}A{sub 2}. In the technique, HE is used to propel circuit elements that perform work against the trapped magnetic field as L or A is reduced, yielding increased I or B. Throughout this paper, the author uses the term flux compression generator (FCG) for these devices, although the reader will find a variety of acronyms in the literature. A good primer on FCG's is by Fowler et al. HE is also used to provide opening and closing switches for HEPP circuits. Closing switches do not require great sophistication, and they don't discuss them …

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