V.B. Yakubov

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.

Explosive magnetic liner systems to study dynamic strength of materials

To study dynamic strength of materials according to the initial liner perturbation growth in Rayleigh-Taylor instability development, three-layer liner systems driven by azimuthal magnetic field pressure have been suggested. This paper demonstrates that 0.4 m diameter disk EMG ensuring currents up to /spl sim/70 MA can be used for this purpose. In the three-layer liner systems, the liner shock-free loading to more than 1 Mbar pressures is therewith possible, with the pressures rising for times longer than 1/spl mu/s or longer than 0.3/spl mu/s in different systems. Here the shock loading of the liners under study is possible up to 3-4 Mbar pressures. Examples of 2D computations of the initial perturbation growth in the liners under study at shock-free and shock pressures up to 1 Mbar, strain rates up to 10/sup 8/sec/sup -1/, and strains up to 200 % are given.

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.

Modeling of MAGO plasma compression by imploding liner

Magnetized plasma with characteristic density 8/spl middot/10/sup 17/ cm/sup -3/ and average temperature 250 eV has been obtained in a MAGO plasma chamber. One and two dimensional magneto-hydrodynamic computations are performed in which a solid density aluminum liner is imploded on the MAGO target plasma. An influence of a liner compressibility, 2-dimensional effects and various heat losses on the compressed plasma parameters are studied. The computations demonstrate that for a liner energy that has already been achieved experimentally the compressed plasma parameters can meet the Lawson criterion and this plasma can provide a large amount of neutrons and X-ray radiation.

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.

Explosive Magnetic Device with a Three-Layered Liner for Radiographic Study of Dynamic Strength of Materials

This paper presents the construction-technology schematic of the device comprising the helical and disk EMGs with a three-layered cylindrical liner (Al-dielectric-Cu) designed for experiments RHSR-0, 1, 2 at the current of 33-35 MA. Polyethylene or water was used as a dielectric layer. The experiments tested successfully the idea to study the dynamic strength of materials by X-raying the growth of amplitude of axisymmetric sinusoidal perturbations machined initially on the outer surface of the examined inner layer of the liner.

Calculations of electric and magnetic fields and joule heating in a vacuum interrupter

High-current circuit breakers based on vacuum interrupter (VI) represent an alternative type of switching equipment suitable for operation under severe climatic conditions. Such devices can offer a number of other technological or environmental benefits compared to the currently used ones. Bringing the performance of the VI-based circuit breakers to the level of ~3 kA nominal currents, ~40 kA rate breaking currents and ~100...200 kV operational voltages requires improved physical models and advanced computational capabilities for the description of their operation. According to contemporary concepts, to ensure working efficiency of a device, in addition to addressing the issues of electrical strength, it is important to account for the system of magnetic field generation between electrodes, which influences the flow of current in the electrode gap and formation of a uniform diffusive discharge. In this paper we present the results of preliminary calculations of electric and magnetic fields for the case of a simplified VI design accounting for the shape of magnetic field generation electrodes and conducting material between them. We explore the effects of magnetic materials used in the chamber design and calculate the force acting on the electrodes and electrode heating by the flowing current. The simulation results can be used to find critical parameters and design regions, and represent the first stage in the modeling of VI operation, which at the next stage should take into account plasma generation at the electrodes.