V. Tz. Gurovich

Nanosecond time scale, high power electrical wire explosion in water

Experimental and magnetohydrodynamic simulation results of nanosecond time scale underwater electrical explosions of Al, Cu, and W wires are presented. A water forming line generator with current amplitude up to 100kA was used. The maximum current rise rate and maximum Joule heating power achieved during wire explosions were dI∕dt⩽500A∕ns and 6GW, respectively. Extremely high energy deposition of up to 60 times the atomization enthalpy was registered compared to the best reported result of 20 times the atomization enthalpy for energy deposition with a vacuum wire explosion. Discharge channel evolution and surface temperature were analyzed by streak shadow imaging and by a fast photodiode with a set of interference filters, respectively. A 1D magnetohydrodynamic simulation demonstrated good agreement with experimental parameters such as discharge channel current, voltage, radius, and temperature. Material conductivity was calculated to produce the best correlation between the simulated and experimentally o...

Numerical simulations of runaway electron generation in pressurized gases

The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.

Underwater electrical explosion of a Cu wire

Results and analysis of a microsecond time scale underwater electrical wire explosion are presented. Experiments were carried out with a Cu wire exploded by a current pulse ⩽100kA with microsecond time duration. The analysis is based on shadow and spectrally resolved streak photography which were used to monitor the evolution of the discharge channel and the shock wave. The obtained data were used for hydrodynamic calculation of the generated water flow parameters, such as pressure and flow velocity distribution between the discharge channel and the shock wave. In particular, the pressure at the discharge channel boundary and the energy transferred to the water were estimated. The results of the calculation have been verified by comparing the measured and calculated trajectories of the shock wave. Based on the results of the calculation the energy transferred to the water was estimated. In addition, the analysis shows that the energy initially deposited in the discharge channel continues to produce mechan...

Pulsed plasma electron sources

There is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E≤105 V/cm and duration ≤10−5 s. In this review, several types of plasma electron sources will be considered, namely, passive (metal ceramic, velvet and carbon fiber with and without CsI coating, and multicapillary and multislot cathodes) and active (ferroelectric and hollow anodes) plasma sources. The operation of passive sources is governed by the formation of flashover plasma whose parameters depend on the amplitude and rise time of the accelerating electric field. In the case of ferroelectric and hollow-anode plasma sources the plasma parameters are controlled by the driving pulse and discharge current, respectively. Using different time- and space-resolved electrical, optical, spectroscopical, Thomson scattering and x-ray diagnostics, the parameters of the plasma and generated electron beam were characterized.

Addressing the efficiency of the energy transfer to the water flow by underwater electrical wire explosion

Experimental and hydrodynamic simulation results of submicrosecond time scale underwater electrical explosions of planar Cu and Al wire arrays are presented. A pulsed low-inductance generator having a current amplitude of up to 380 kA was used. The maximum current rise rate and maximum power achieved during wire array explosions were dI/dt≤830 A/ns and ∼10 GW, respectively. Interaction of the water flow generated during wire array explosion with the target was used to estimate the efficiency of the transfer of the energy initially stored in the generator energy to the water flow. It was shown that efficiency is in the range of 18%–24%. In addition, it was revealed that electrical explosion of the Al wire array allows almost double the energy to be transferred to the water flow due to efficient combustion of the Al wires. The latter allows one to expect a significant increase in the pressure at the front of converging strong shock waves in the case of cylindrical Al wire array underwater explosion.

Characterization of converging shock waves generated by underwater electrical wire array explosion

Results of ∼200 kbar pressure generation at 50 μm distance from the implosion axis of the converging shock wave produced by an underwater electrical explosion of a cylindrical wire array are reported. The array was exploded using a submicrosecond high-current generator (stored energy of ∼4.2 kJ, current amplitude of ∼325 kA, rise time of ∼1 μs). Multiframe shadow imaging of the shock wave was used to determine its time of flight. These data were applied for calculating the pressure at the vicinity of the implosion axis using one dimensional hydrodynamic calculations and the Whitham approach. However, it was found that in the case of wire array radius ≤5 mm, multiframe imaging cannot be used at the final stage of the shock wave implosion because of possible changes in the optical properties of the water. Optical and spectroscopic methods based on either the change in the refraction index of the optical fiber or spectroscopy of the plasma formed inside the capillary placed at the implosion axes were used fo...

Spectroscopic research of underwater electrical wire explosion

Results of spectroscopic research in the visible range of light of the radiation generated by underwater electrical wire explosions (UEWE) are presented. A pulsed generator with an output voltage of ∼110kV, current of ∼70kA, and rise time of ∼60ns was used for electrical explosion of Cu wires 0.1mm in diameter and 50mm in length. It was shown that UEWE is not governed by the “polarity” effect, which plays an important role in electrical wire explosions in vacuum. The results of detailed space- and time-resolved spectroscopic measurements show that the radiation spectrum differs significantly of the spectrum expected from the exploding wire. A model is suggested based on the formation of a few μm “water” plasma layer in the vicinity of the exploding wire plasma which efficiently absorbs the radiation of the exploding wire.

Generation of converging strong shock wave formed by microsecond timescale underwater electrical explosion of spherical wire array

A study of generation of converging strong shock wave using microsecond underwater electrical explosion of spherical Cu-wire array is presented. Hydrodynamic simulations coupled with the equation of state for Cu and water, deposited energy, and the magnetic pressure were used to calculate the water parameters in the vicinity of the implosion origin. The results of simulations agree with the shock wave time-of-flight and energy delivered to the water flow and show that in the vicinity (diameter of ∼12 μm) of an implosion one can expect water pressure of ∼6 TPa, temperature of ∼17 eV, and compression of ∼8.

Generation of a 400 GPa pressure in water using converging strong shock waves

Results related to the generation of an extreme state of water with pressure up to (4.3 ± 0.2)·1011 Pa, density up to 4.2 ± 0.1 g/cm3, and temperature up to 2.2 ± 0.1 eV in the vicinity of the implosion axis of a converging strong shock wave are reported. The shock wave was produced by the underwater electrical explosion of a cylindrical Cu wire array. A ∼8 kJ pulse generator with a current amplitude ≤550 kA and rise time of 350 ns was used to explode arrays having varying lengths, radii, and number of wires. Hydrodynamic numerical simulations coupled to the experimental data of the shock wave propagation in water, rate of energy deposition into the array, and light emission from the compressed water in the vicinity of the implosion axis were used to determine the pressure, density, and temperature profiles during the implosion. Results of a comparison between these parameters obtained with the SESAME and quantum molecular dynamics data bases of equation of state for water are reported as well. Also, the ...

Implosion in water medium and its possible application for the inertial confinement fusion target ignition

A numerical and self-similar analysis of the generation of implosion in water medium in cylindrical and spherical geometries is presented. The following interaction of the implosion wave with a deuterium-tritium mixture target is analyzed. It was found that the established converging cumulative water flow is self-similar, in spite of the complexity of the implied equations of state. Results of an idealized model indicate that, using a spherical geometry setup with 7.5mm external radius of the water layer and ∼35kJ total deposited energy, a ∼1.5×1014 neutron yield during ∼1.5ns time can be achieved. The obtained results suggest that ignition of deuterium-tritium target by implosion in water medium can be considered as a promising method for inertial confinement fusion.