V.K. Chernyshev

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.

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.

Electroexplosive foil 500 kV current opening switch characteristics research

The increase of explosive magnetic generator power may be achieved by selecting construction of foil opening switch (FOS), having extended break surface. In this work, the results of FOS models tests are presented, which were powered from a capacitor bank with the energy of 225 kJ and output voltage of 100 kV. The time (T/4) of opening switch powering was 4 /spl mu/sec. In inductive load L=0.9*10/sup -6/ H connected through a spark gap parallel to the opening switch, the impulse of current derivative with amplitude of /spl sim/0.6 10/sup 9/ A/sec was received. Amplitude of voltage pulse on the FOS model was 550 kV, pulse duration at semiheight was /spl sim/0.5 /spl mu/sec. Electric strength to electroexplosion products of copper foil was 9.2 kV/cm. Empirical dependence of copper specific resistance upon the specific energy is experimentally obtained and it may be used for engineer computations for estimation and prediction of copper conductors electroexplosion processes. FOS models tests results demonstrated principal possibility of current opening switch construction, which is able to operate with EMG at stored energy of more than 90 MJ and intended for obtaining powers more than 2/spl middot/10/sup 13/ W.

Explosive Opening Switches For Fast - Operating Helical EMGs.

In plasma chamber experiments on magnetized Plasma preheating in MAG0 system I 1 1 fast operating helical explosive magnetic generators (HF.HG) are used as a Power source . The generator are Provided with special explosive current opening switches to increase Power and output energy of the source. In work C 2 1 we have considered some investigation data of explosive current opening switch,obtained on flat models and full-scale specimen. The Present Paper gives an additional material of these investiaations on the option of opening switch optimum Parameters and on increase of the source output Power and energy at the account of HEMG contour additional comPression by opening switch charge.

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.

Simple economic explosive magnetic generator of high pulsed power

A source of electromagnetic energy made on the basis of two loop generators, supplied by a helical explosive magnetic generator, is described in the paper. A possibility has been considered of the loop generators usage to build up a pulsed power system suitable for condensed liners implosion study.

High energy imploding liner experiment HEL-1: experimental results

The imploding liner is a cylinder of conducting material through which a current is passed in the longitudinal direction. Interaction of the current with its own magnetic field causes the liner to implode. In August, 1996, a high energy liner experiment (HEL-1) was conducted at the All-Russia Scientific Research Institute (VNIIEF) in Sarov, Russia. A 5 tier 1 meter diameter explosive disk generator provided electrical energy to drive a 48 cm outside diameter, 4 mm thick, aluminum alloy liner having a mass of about 1 kg onto an 11 cm diameter diagnostic package. The purpose of the experiment was to measure performance of the explosive pulse power generator and the heavy imploding liner. Electrical performance diagnostics included inductive (B-dot) probes, Faraday rotation current measurement, Rogowski total current measurement, and voltage probes, flux loss and conductor motion diagnostics included current-joint voltage measurements and motion sensing contact pins. Optical and electrical impact pins, inductive (B-dot) probes, manganin pressure probes, and continuously recording resistance probes in the central measuring unit (CMU) and piezo and manganin pressure probes, optical beam breakers, and inductive probes located in the glide planes were used as liner symmetry and velocity diagnostics. Preliminary analysis of the data indicate that a peak current of more than 100 MA was attained and the liner velocity was between 6.7 km/sec and 7.5 km/sec. Liner kinetic energy was between 22 MJ and 35 MJ.

Magnetic opening switch shaping the pressure pulse for high-speed liner implosion by high-current explosive generator

The paper presents the results of the experiment in which the liner implosion was realized by a pressure pulse shaped by a magnetic opening switch. The current of the high-current explosive generator flows through the ring element of the magnetic opening switch during the time of 430 /spl mu/s till it rises to 10 MA. The diameter of the copper ring element was 100 mm, length along the axis was 15 mm, and its thickness was 1.2 mm. The ring element was connected to the current-conducting electrodes by the bridges only 0.2 mm thick. Under the effect of magnetic pressure from the flowing ultra-high current the ring element expands in the radial direction. A thin bridge 0.2 mm thick is easily cut in the beginning of the element expansion, and then the ring element is only in sliding contact with the electrodes. Having run the distance of 14 mm, the ring element slides off the current-conducting electrodes. Separation of the ring element happened 30 /spl mu/s prior to the explosive high-current generator operation completion and prior to reaching the maximum current in it. At the moment of separation the rate of the ring element radial expansion was 1.5 mm//spl mu/s. A volumetric arc appears in the gap between the ring element and the current- conducting electrodes. Under the effect of magnetic pressure of /spl sim/ 10/sup 9/ Pa the magnetized plasma spreads into a toroidal cavity of the coaxial above the imploding cylindrical liner. The peak current in the high-current explosive generator was 19 MA. The amplitude of current in the toroidal cavity of the coaxial above the imploding liner generated after the separation of the opening magnetic switch ring element from the electrodes was 18 MA, the time of current rise from 4 MA to 18 MA in the coaxial above the liner was 8 /spl mu/s. The aluminum liner initial diameter was 100 mm, the wall thickness was 1 mm. The radial rate of the liner implosion was 6.2 km/s. The analysis demonstrates that the liner acceleration was provided by a combined action of gaskinetic and magnetic pressure of magnetized plasma. The advantage of the magnetic opening switch is its design simplicity, and also the fact that the pressure pulse shaping is not accompanied by the high-current generator current interruption but is realized by a continuous travel of the conducting medium towards the liner. This increases the efficiency of energy usage for liner implosion. The disadvantage is that as the liner radius decreases the pressure in it increases less than in case of direct current transfer to the liner. In the experiment considered the toroidal cavity of the coaxial above the liner was not vacuumized. The liner implosion rate may be higher in case the cavity is vacuumized and in case the ring element slide-off moment in the magnetic opening switch is delayed towards the moment of peak current in the high-current generator.

GAS PONDERMOTOR UNIT WITH A COMPRESSIBLE ACCELERATION CHAMBER

Studies on magnetized Plasma heating in a gas chamber.having MHD nozzle are reported in WOrK C1.23. Magnetized Plasma i s accelerated by a magnetic fields vp to velocites of 10 cmlsec and is heated, during decelerating in a shock wave. Explosive magnetic generator (EMG) serves as an energy source. Maximum neutron Yield , received in a chamber,was 4 10 neutron / Per a Pulse C21. Neutron Pulse duration was 1 to 2 p e c . The Principal way for further Plasma temperature increase UP to thermonuclear ignition is additional adiabatic compression of Plasma, heated in a shocK wave at HHD nozzle output . This tasK could be easier if it were Possible to increase hot plasma lifetime by several fold. It is assumed,that the most Probably cause of m i c K Plasma cooling in d hot area of a chamber decelerdtlon section, giving rise to neutron Pulse durdtion of * Zpsec., is a delivery of insulator vapours into this area from a deceleration section. Insulator vapours and gas, located near the insulator, are frozen into a higher magnetic field , as they are located at a small radins . This PdPt of gas dPtPrminPs now neutron Yield out of the chamber, 3s 1 t obtains the most velocity ,and the neutron Pulse duration is determined by the Presence of insulutor vapours. 8