John E. Osher

Operating characteristics and modeling of the LLNL 100-kV electric gun

In the electric gun, the explosion of an electrically heated metal foil and the accompanying magnetic forces drive a thin flyer plate up a short barrel. Flyer velocities of up to 18 km/s make the gun useful for hypervelocity impact studies. The authors review the technological evolution of the exploding-metal circuit elements that power the gun, describe the 100-kV electric gun designed at Lawrence Livermore National Laboratory (LLNL) in some detail, and present the general principles of electric gun operation. They compare the experimental performance of the LLNL gun with a simple model and with predictions of a magnetohydrodynamics code. >

Application of a 100-kV electric gun for hypervelocity impact studies

Abstract The Lawrence Livermore National Laboratory 100-kV electric gun has been used to launch flat-plate projectiles for use in studies of spall and hypervelocity impact penetration of thin plates. Impactors were 0.3-mm thick Kapton with dimensions and velocities ranging from 100 mm 2 at 4 km/s to 10 mm 2 at 18 km/s. A Fabry-Perot laser velocimeter, an electronic streak camera, and a flash x ray were used as diagnostics of the flyer-plate impact on the selected specimen. Experiments generally included the recovery of the remnant specimen and fragments for detailed examination, permitting a study of incipient spall, onset of melting, and fraction fragmented. Experiments to be described include spall measurements on simple and composite target walls at normal and oblique incidence and “reverse ballistics” impacts of the thin-plate impactor on a stationary penetrator (e.g., Kapton impactors at 15 km/s incident on rods of steel, aluminum, and lead) for calibration of hypervelocity impact codes.

Hypervelocity acceleration and impact experiments with the LLNL electric guns

Abstract In the electric gun, the explosion of an electrically heated metal foil and the accompanying magnetic forces are used to accelerate a thin flyer plate to velocities as high as 18 km/s. Here we report preliminary results of a study to extend this capability to the acceleration of projectiles or particles ranging in size from micrometeorites to chunky projectiles with a mass as high as 0.5 g. We also have started code calculations of projectile impacts on thick aluminum witness plates for comparison with observations of experimentally produced cratering.

RTNS-II Neutron Sources: Status Report

Experience with neutron sources consisting of air-insulated 400 kV deuteron accelerators and tritium targets which rotate at 5000 rpm is reported. These accelerators are part of the Rotating Target Neutron Source-II (RTNS-II) facility. A review of the accelerator design is given. Operation of the prototype accelerator using hydrogen beams is discussed in detail. The parameters are tabulated for the first accelerator operated as a neutron source in November, 1978. Additional terminal pumping has reduced the radiation level from bremsstrahlung by at least a factor of ten. Ion source performance with deuterium has not been as good as that obtained with hydrogen. Beam divergence at the acceleration column exit is also observed. Future efforts include the fabrication of large diameter targets and design changes to improve source operation.

The impact of flat, thin plates on aluminum targets in the 5–10 km/s velocity range

Abstract The purpose of the study was to investigate the effect of the impact of a thin membrane on aluminum in the velocity range 6–10 km/s. The impulsive load delivered by a membrane impact will exceed the momentum/area of the membrane because of rebound, blow-off of vaporized membrane material, and ejection of molten and fractured material from the target (impulse gain). One of the objectives of the study was to quantify the impulse gain in the velocity range of interest. Also of interest was the physical damage to the target including spall, melting and fracture. Understanding these damage mechanisms is important for protecting spacecraft from the impact of space debris and meteoroids. Simple theories account for the flyer rebound, but hydrodynamic modeling is required to treat the blow-off of target material. At lower velocities, the blow-off is negligible, but at10 km/s calculations show it to be equal to the rebound momentum for one-dimensional (1-D) impacts. The modeling of three-dimensional (3-D) experiments revealed large effects at the edge of an impacting membrane, prompting an emphasis on 1-D pressure profile experiments.

Characteristics of hypervelocity impact debris clouds

Abstract This paper describes an experimental investigation of hypervelocity impact debris clouds produced by impacting metal rods with Kapton flyers in an electric gun facility. Soft copper witness plates placed in the path of the debris were cratered and coated with rod material. From the sizes of the craters on the witness plates we could obtain values for a cratering parameter containing the ,asses and velocities of the debris fragments that formed the craters. By combining the cratering parameter with rough estimates of the fragment masses, we then estimated the fragment velocities. By measuring the thickness and extent of the coating on the witness plates, we obtained a bound on the amount of material vaporized by the impact.

1 MJ electric gun facility at LLNL

The 1 MJ electric gun system at Lawrence Livermore National Laboratory (LLNL) is described. The primary motivation for building this electric gun system was to throw large-area, thin-plate impactors with areas up to 930 cm/sup 2/. Attention is given to electric gun operation, the capacitor bank, the target chamber, diagnostics, launch capability, and modeling tools. >

Application of Fabry-Perot velocimetry to hypervelocity impact experiments

The Fabry-Perot (F-P) velocimeter is our main diagnostic tool for hypervelocity impact experiments with the electric gun. Because of its immunity to electromagnetic interference F-P velocimetry is well suited to studying the performanceof flyers providing data on velocity calibration acceleration characteristics and material erosion as well as spallation of various materials under high-velocity impact measurement of impact pressure pulses and Hugoniot measurements of composite materials. We present results and data from selected experiments and compare them with code predictions. 1.

HUGONIOT MEASUREMENTS ON A SLURRY OF FINELY DIVIDED TUNGSTEN AND PLASTIC

A previous paper reported hugoniot measurements on a two-phase material consisting of a matrix and an embedded material (silica- phenolic) using the LLNL electric gun facility. The results showed a good bit of scatter in the measurements. This was attributed to the grossly heterogeneous nature of the material. Measurements have since been made on a slurry of finely divided tungsten powder in a plastic, greatly reducing the scale of the inhomogeneity. The results show greatly reduced scatter, as expected from the above interpretation. 4 refs., 2 figs.

Diagnostics for mirror machines

ABSTRACT This paper is subdivided into three chapters to match three corresponding lectures. The goals of the first chapter are to define the neutral-beam-heated, quasi-d.c. mirror confinement systems under discussion here and to give a general example of mirror diagnostics by listing and very briefly discussing the diagnostics used on the 2XIIB experiment at the Lawrence Livermore Laboratory. The second chapter develops mirror machine diagnostics in more detail, and adds background for a few selected diagnostics of particular importance to mirror machine studies. The third chapter discusses the special diagnostic needs of future mirror machines, with emphasis on diagnostics involving the higher-power neutral beams used with them.