Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2015 number 1

A device based on a super–power disk explosive magnetic generator for producing an x–ray pulse with energy exceeding the target ignition threshold is presented and substantiated.

This paper investigates the feasibility of using the PHELIX facility for generation of warm dense matter (WDM), i.e., substance at densities of the order of 0.01–1.00 of the solid matter density and a temperature of 1–10 eV, by electric explosion of a thin cylindrical metal foil enclosed in an insulator. It has been shown this system can be used to produce a significant volume of uniform WDM with a density of 0.1–1.0 g/cm³ and a temperature of 3–4 eV, sufficient for electrical measurements. A method of determining WDM parameters based on electrical measurements and foil boundary velocimetry is described.

This paper presents the results of tests of a facility based on a ten-element disk magnetocumulative generator and an explosive opening switch. A current of 10 MA with a characteristic rise time of ≈0.5 μs was obtained by breaking a circuit with a current of 18 MA in a load with an inductance of 16 nH, which is equivalent to the inductance of the chamber with a multiwire liner.

This paper discusses one type of power generators — a disk explosive generator with flat disk elements and metal inserts. A technique of numerical simulation of the operation of this generator is proposed. The principle of operation and the design of the disk explosive magnetic generator are described. The results of calculations and experiments are presented.

Several possibilities of preamplifier energy and power increasing are considered: using a more powerful (HMX–based) conical HE–charge in the central tube of the magneto–cumulative generator, using a magnetic flux finish pressing out device with axial initiation of the HE charge, and increasing the inner diameter of the helix. A magneto–cumulative generator (MCG) with a helix 280 mm in diameter (MCG–280) is developed. The new preamplifier has a power of ≈400 GW and is able to power a ten–element DMCG480 with an initial inductance of ≈0.2 m H by a current of ≈10 MA with a characteristic current rise time (by a factor of e at the final stage of its operation) τ_e = 32 μs.

This study is a contribution into the development of physicotechnical foundations for generation of powerful nanosecond high–current pulses on the basis of explosively driven magnetic flux compression generators. This problem is solved by using inductive storage of energy for matching comparatively low-voltage explosively driven magnetic flux compression generators and high–impedance loads; short forming lines and vacuum diodes. Experimental data of charging of forming lines are given.

The paper describes a small-size explosive current source with controllable output voltage shaping a megaampere current pulse. This energy source comprises a helical explosive magneticgenerator and an explosive sectionalized current opening switch and is designed to power gas-discharge chambers of the plasma focus type. Control of the output voltage of the pulsed current source is performed in such a manner that in each of the series-connected sections of the explosive current opening switch, voltage is generated with a given time shift relative to the neighboring section.

The paper presents the Gamma–4 four-module electrophysical facility project developed for radiation physics research. For this facility, we have developed and tested a typical module which, with a matched load, generates an electrical pulse with voltage and current amplitudes of up to 2 MV and 750 kA, respectively, and with a half-height duration of 60 ns. 700 shots were performed which conformed the operating parameters and reliability of the module. Layouts of the facility for the modes of synchronous (with accuracy of ±3 ns) operation of the modules with vacuum electron diodes and with a current summator to generate soft x-ray pulses have been developed.

The Gamma–4 four-module electrophysical facility has been designed for generation of powerful bremsstrahlung radiation pulses. One of the basic modes of operation of the facility is the operation of each module with its autonomous vacuum diode. The electrical characteristics of the high-current self-magnetic pinch diode of the typical module of the Gamma–4 facility (the Gamma–1 pulsed electron accelerator) are determined. It is shown that by changing the diode impedance in the range 1.3–4.0 Ω, it is possible to implement operation modes in which bremsstrahlung radiation pulse with a limiting quantum energy of 0.9 to 2.0 MeV are formed.

The accelerating tube of Gamma–4 electrophysical facility standard module is presented. This accelerating tube is a component part of the energy transmission system of the module which provides delivery of the high-voltage electric pulse from the forming system output to the load unit. A specific feature of the tube design is the use of a dielectric lens to equalize the potential over the surface of the sectioned insulator. The lens made it possible to lower the electric field strength by 30% in the region of the most stressed dielectric rings, thus reducing the probability of the insulator breakdown. To increase the resource of the tube, its dimensions were selected based on the calculated average electric field intensity over the insulator surface equal to 55 kV/cm. The inductance of the tube was 87 nH. 230 shots of the Gamma–1 accelerator were performed using the proposed accelerating tube with an insulator voltage of 2.7 MV. No electrical breakdowns of the insulator were observed in these shots.

This paper presents the results of measurements of the generation parameters of the Gamma–4 electrophysical facility designed to generate high-power bremsstrahlung pulses with a duration of ≈50 ns. Five shots of the Gamma–1 accelerator were performed, in which the bremsstrahlung exposure dose was measured at a distance of 20, 30, and 60 cm from the accelerator target. It is shown that the experimental data correspond to the radiation field of a point cosine source with a relative error of 13%. The spatial distribution of the bremsstrahlung exposure dose of the Gamma–4 facility was reconstructed taking into account the spatial orientation of the irradiators. The bremsstrahlung exposure doses at a distance of 15 cm from the modules targets are presented.

A synchronization system for the Gamma–4 four-module electrophysical facility has been developed. It has been shown that the synchronization system should provide triggering (with precision not worse than ±3 ns) of the high-voltage gas-filled trigatron-type switches of the facility modules (144 spark gaps with an operating voltage of 1 MV), the pre-pulse switches of the modules (24 spark gaps with an operating voltage of 3 MV) and eight Arkad'ev-Marx generators (40 spark gaps with an operating voltage of 100 kV).

This paper presents the results of laboratory and explosive experiments with a plasma focus discharge Mather-type chamber at a discharge current amplitude of 1.3–1.4 MA. It has been found that in laboratory experiments, the yield of a deuterium-deuterium neutrons reached 10¹¹, and in an explosive experiment using the chamber filled with a deuterium-tritium gas mixture, the integral yield of a deuterium-tritium neutrons with an energy of 14 MeV was more than 10¹² neutrons.

The behavior of a slow burn wave propagating over a precompressed thermonuclear fuel heated by several shock waves generated by a laser pulse is studied. It is shown that such a burn wave can rapidly increase the fuel density ahead of the wave front and transform to a pair of detonation waves moving in the opposite directions. Hydrodynamic equations with a linear velocity profile are solved. It is found that the proton beam intensity necessary for ignition increases with the initial fuel density in accordance with the known formula generalizing results of two-dimensional simulations. A possibility of using results of one-dimensional simulations for determining the energy of ignition of a cylindrical target is discussed.

The paper presents the results of model experiments to test a new field liner driver based on the disk explosive magnetic flux compression generator, results of driver development, and revised two-dimensional magnetohydrodynamic simulations of liner implosion.

This paper describes a method and device for generating a mega-ampere quasi–trapezoidal current pulse of given amplitude and duration in a liner load. The experimental device consisting of a current source based on a helical explosive magnetic generator (HEMG) produced a current pulse in the liner load with an amplitude of ≈10 MA and controlled duration and current rise and decay times. The use of this source to accelerate cylindrical liners allows the study of the mechanisms of material damage in converging geometry, in which new damage effects may occur due to the multidimensional nature of the loading conditions.

The MEG–2D two-dimensional Eulerian design procedure was used for magnetohydrodynamic simulation of the megaampere current switching process by an explosive opening switch. This paper presents simulation results for the current switching of a helical magnetocumulative generator (MCG) by explosive opening switches of different types at the same parameters of the switching scheme, thickness of the breaking conductor made of copper foil, the breaking current, and the number of opening switch elements. Simulation results for current switching by an explosive opening switch with a ribbed barrier for different thickness of the broken copper foil conductor are also presented. In the case of using a foil 0.3 mm thick, a ribbed barrier with steel inserts on the ribs with optimal parameters was investigated. It is shown that at a foil thickness less than 0.2 mm, decreasing the depth of the groove in the barrier does not lead to an increases in the time of triggering of the opening switch.

This paper presents a review of publications on the use of electrically exploded foil opening switches to form current pulses up to 100 MA (up to 45 MA in experiments) with a rise time of 0.1–10.0 μs. Physical schemes and models are considered, and the efficiency of foil opening switches for existing and advanced facilities is analyzed.

This paper presents the results of experimental and numerical studies of the behavior of metallic shaped-charge jets (SCJs) through which electric current flows. The possibility of decreasing and increasing the depth of penetration of SCJs into targets is considered. The concepts are introduced of the critical current density and the ideal shape of the current pulse at which necking magnetohydrodynamic instability develops in the jet, accompanied by volume explosion of the SCJ elements at their exit from the interelectrode gap. The development of necking magnetohydrodynamic instability in the SCJ and subsequent volume explosion of the jet material lead to a reduction in the jet length and density, and as a consequence, to a decrease in the depth of SCJ penetration into the target. It has been shown that this process can be controlled by changing the electric pulse parameters. The possibility of increasing the depth of SCJ penetration into targets under conditions where the electric current flowing through the SCJ is less than the critical value is analyzed. The process of heating of SCJs of different materials (Cu, Fe, Mo, Ta, W, etc.) by the electric current flowing through them is considered. It is shown that the use of electric current to heat SCJs may be a promising approach to increase the depth of penetration of SCJs into targets.

This paper presents the results of an experimental study of the temporal waveforms of the pressure amplitude in different regions of flat electrically exploded foils of M1T copper, AD1M aluminum, L63 brass, 80NKhS nickel alloy, VT1–00 titanium, and tin-clad lead. In the case of high-conductivity foils, explosion starts from the foil ends with a subsequent stronger growth of pressure in the centrally axial region of the exploded foil. It is shown that the electrical resistivity of the exploded metal is an important parameter that influences the uniformity and simultaneity of the explosion.

Results of an experimental-theoretical study of spallation in synthetic diamonds are presented. In this study, data were first obtained on dynamic tensile strength of poly– and single-crystal diamond samples at mechanical loads of up to 0.34 TPa and strain rates of 10–100 μs^–1. Shock-wave loading was performed by 70 ps laser pulses on a Kamerton–T facility using a Nd:glass laser (second harmonics λ = 527 nm, pulse energy of up to ≈3 J) at intensities of ≈8 TW/cm². The obtained maximal value of the spall strength ≈16.4 GPa is 24% of the theoretical ultimate strength of diamond. Raman scattering experiments showed that a small amount of diamond was graphitized in the spall area on the backside of the sample.

New ceramic materials based on yttrium oxide Y₂O₃ with isovalent (Yb₂O₃, Nd₂O₃, and Lu₂O₃) and heterovalent (ZrO₂ and HfO₂) components are synthesized, and their spectroscopic properties are investigated. Possible channels of losses in the gain of stimulated radiation in the radiative transitions of Nd³⁺ and Yb³⁺ ions in ceramics with heterovalent additives are studied. The results of measurements of Y₂O₃ ceramics doped with zirconium and hafnium ions, the emission bandwidth and the lifetimes of the ⁴F_3/2 and ²F_5/2 levels of Nd³⁺ and Yb³⁺ ions, respectively, are presented. It is shown that the nonradiative population of the ⁴F_3/2 levels of neodymium ions is due to their dipole-dipole interaction with Zr³⁺ and Hf³⁺ ions. Laser generation in [(Yb_0.01Lu_0.24Y_0.75)₂O₃]_0.88(ZrO₂)_0.12 ceramics with disordered crystalline structure was achieved at a wavelength of 1034 nm with a differential efficiency of 29%.

A mobile testing complex prototype on the basis of an explosive magnetic generator (MTC EMG) is developed to simulate a lightning current pulse. The main element of this complex is a current pulse generator comprising a EMG with a pulse transformer for energy release into the load. The electric chain of the MTC EMG is theoretically analyzed taking into consideration energy losses in active resistances in the primary circuit of the transformer and the inductive-resistive nature of the load, which resulted in the minimization of energy losses in the primary circuit depending on the electric chain parameters. It was found that, if the energy losses are minimized, the efficiency of transferring the EMG energy into the load exceeds 50%. As a result of the field tests of the MTC EMG, its basic characteristics were determined and the waveforms of the current pulses and voltages in the load were obtained. It is shown that the results of the mathematical simulation of current pulses in the load are in good agreement with the experimental data.