V.N. Mokhov

HEL-1: a DEMG based demonstration of solid liner implosions at 100 MA

In August 1997, the Los Alamos National Laboratory (LANL) and the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) conducted a joint experiment in Sarov, Russia to demonstrate the feasibility of applying explosive pulsed power technology to implode large scale, high velocity cylindrical liners. Kilogram mass metal liners imploding at velocities of 5-25 km/sec are useful scientific tools for producing high energy density environments, ultra-high pressure shocks and for the rapid compression of plasmas. To explore the issues associated with the design, operation and diagnosis of such implosions, VNIIEF and LANL designed and executed a practical demonstration experiment in which a liner of approximately 1 kg mass was accelerated to 5-10 km/sec while undergoing a convergence of about 4:1. The scientific objectives of the experiment were three-fold: first to explore the limits of very large, explosive, pulse power systems delivering about 100 MA as drivers for accelerating solid density imploding liners to kinetic energies of 25 MJ or greater; second to evaluate the behavior of single material (aluminum) liners imploding at 5-10 km/s velocities by comparing experimental data with 1-D and 2 D numerical simulations; and third, to evaluate the condition of the selected liner at radial convergence of 4 and a final radius of 6 cm. A liner of such parameters could be used as a driver for the equation of state measurements at megabar pressures or as a driver for a future experiment in which a magnetized fusion plasma would be compressed to approach ignition conditions.

Results of a 100-megaampere liner implosion experiment

A very high-current liner implosion experiment was conducted, using an explosive magnetic-compression generator (EMG) to deliver a peak current of 102 /spl plusmn/ 3 MA, to implode a 4.0-mm-thick aluminum liner. Analysis of experimental data showed that the inner surface of the liner had attained a velocity of between 6.8-8.4 km/s, consistent with detailed numerical calculations. Both calculations and data were consistent with a final liner state that was still substantially solid at target impact time and had a total kinetic energy of over 20 MJ.

On the feasibility to achieve high pressures with disk EMG driven impacting liners

Devices for producing 10-30 Mbar pressures in cylindrical targets of /spl sim/1 cm radius would be unique tools to study material properties under extreme conditions for a variety of research and application purposes. The paper presents results of theoretical and computational studies demonstrating the feasibility of this. The multi-module disk EMG themselves and especially those with an electrically exploded opening switch developed by VNIIEF are shown to be able to ensure the required acceleration of solid impacting liners, e.g., two-layered liners made of aluminum (on the outside) and molybdenum or tungsten (inside), up to 15-20 km/s velocities. The impacting liners optimal in their match to two considered energy sources have radii from /spl sim/7 cm to /spl sim/3 cm for targets of /spl sim/1 cm radius. Results of 2D magnetohydrodynamic liner compression computations are also presented, according to which the 2D effects of the liner interaction with end components may not lead to considerable violations of the desired 1D pattern of the liner impact on the target.

Modeling and analysis of the high energy liner experiment, HEL-1

A high energy, massive liner experiment, driven by an explosive flux compressor generator, was conducted at VNIIEF firing point, Sarov, on August 22, 1996. We report results of numerical modeling and analysis we have performed on the solid liner dynamics of this 4.0 millimeter thick aluminum liner as it was imploded from an initial inner radius of 236 mm onto a central measuring unit (CMU), radius 55 mm. Both one- and two-dimensional MHD calculations have been performed, with emphasis on studies of Rayleigh-Taylor instability in the presence of strength and on liner/glide plane interactions. One-dimensional MHD calculations using the experimental current profile confirm that a peak generator current of 100-105 MA yields radial liner dynamics which are consistent with both glide plane and CMU impact diagnostics. These calculations indicate that the liner reached velocities of 6.9-7.5 km/s before CMU impact. Kinetic energy of the liner, integrated across its radial cross-section, is between 18-22 MJ. Since the initial goal was to accelerate the liner to at least 20 MJ, these calculations are consistent with overall success. Two-dimensional MHD calculations were employed for more detailed comparisons with the measured data set. The complete data set consisted of over 250 separate probe traces. From these data and from their correlation with the MHD calculations, we can conclude that the liner deviated from simple cylindrical shape during its implosion. Two-dimensional calculations have clarified our understanding of the mechanisms responsible for these deformations.

Possibility of low-dense magnetized DT plasma ignition threshold achievement in a MAGO system

The MAGO concept using the thermonuclear target with DT gas preliminary heating up to kiloelectronvolt range temperatures, which sufficiently enables the reduction of requirements of the compression rate (to 10 km/s) and the compression degree (to several hundreds) of the target, is investigated. The MAGO chamber with the Laval supersonic annular nozzle is used for plasma preheating. In this chamber magnetized plasma is accelerated up to 1000-km/s velocities and heated by collisionless shock waves. Systems with liner and magnetic compression are considered for the subsequent plasma compression. Energizing of a real-size system can be supplied by the magnetic flux compression generators with energy 100−500 MJ. Experiments close to the threshold of ignition can be conducted proportionally in 2−3 times reduced systems. Then the energy required will be 10–30 times less than in a real-size system.

Dynamic Copper and Polyethylene Strengths in Shockless Loading to 15 GPA According to the Data of Explosive Magnetic Experiments with Cylindrical Three-Layer Liner Systems

This paper presents the computational analysis of an experimental three-layer liner system, Al-polyethylene-Cu and Al-water-Cu, designed for the study of dynamic strength of low-density and high-density materials using the perturbation growth caused by the Rayleigh-Taylor instability. Copper and polyethylene dynamic strength models developed by VNIIEF are used. Comparison between computations and experiments showed good agreement with a model for copper obtained previously from analysis of high-pressure explosive driven shock-free experiments. The data also allowed us to refine a model for polyethylene obtained from the analysis of previous experiments.

Linear experiment on verification of Rayleigh-Taylor instability magnetic stabilization effect (joint LANL/VNIIEF experiment Pegasus-2)

A liner implosion experiment was conducted on facility Pegasus-2, in which two perturbation type growth was compared. On one half (through height) of the cylindrical liner sinusoidal azimuthally symmetric perturbations were produced. On the other liner half the perturbations were of the same wavelength and the same amplitude, but the angle between the wave vector and the cylinder axis was 45/spl deg/ (screw perturbations). The experimental radiographs show that there is essentially no screw perturbation growth, while the azimuthally symmetric perturbations grow many-fold. This result agrees with the theoretical predictions.

On feasibility to achieve a high longitudinal symmetry of cylindrical metal liners compressed by currents from most powerful disk EMG

Due to their interaction with end current leads during implosion, high-energy cylindrical liners driven by disk EMG currents can gain considerable longitudinal asymmetry, like, for example, in the joint RF-US experiment HEL-1 (1996), which agrees with computations using various 2D techniques. This paper using 2D DRAKON and MEDUZA computations demonstrates the possibility to cardinally improve the longitudinal compression symmetry for this liner type as compared to that in HEL-1. The influence of liner geometry and strength parameters as well as ponderomotive unit end current lead parameters on the liner compression longitudinal symmetry is studied. Data is obtained which is needed for selection of the ponderomotive unit for the second potential joint VNIIEF/LANL explosive magnetic experiment (HEL-2) in order to achieve a high longitudinal symmetry of impact of the cylindrical solid liner on the target at liner velocity up to 15 km/s.

Results of Russian/US high-performance DEMG experiment

In November 1992, the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF), Arzamas-16, Russia and the Los Alamos National Laboratory, Los Alamos NM, USA embarked on a historic effort to conduct a joint explosive pulse-power experiment. With the concurrence of the Ministry of Atomic Energy (Russia) and the Department of Energy (US), the two laboratories entered into a laboratory-to-laboratory collaboration in the areas of very high-energy pulse power and ultrahigh magnetic fields in order to explore problems of mutual scientific interest. The first experiment to be planned was an explosively powered, fast, high-current pulse-power system demonstration. The experiment used a flux compressor, inductive store, and high-current opening switch to demonstrate the feasibility of supplying many megajoules of electrical energy, on microsecond time scales, to high-energy density physics experiments. The experiment was conducted in Arzamas-16 on September 22, 1993.

Study of high-energy liner compression in HEL-1 experiment

The paper describes arrangement and the results of the first joint experiment between VNIIEF and LANL with explosive magnetic generators (EMG) of 1 m diameter and a nonevaporating liner. The experiment took place in August 22, 1996. The goal of the experiment was to accelerate magnetically cylindrical relatively thin aluminum liner and to get kinetic energy of 20 MJ or more. As the energy source for the experimental device we chose 5-module DEMG of 1000 mm diameter, tested many times in the experiments for rigid and liner loads. This EMG can store more energy than any other EMG created at VNIIEF. The physical scene of the liner unit was chosen so that the growth of disturbances would have less influence on the liner shape during flight, especially on the liners inner surface. The shape of glade plane on which the liner slides during flight and the way of contact liner with walls were chosen on the grounds of 2-D calculations, proceeding from the necessity to ensure electrical contact during the liner flight.