A time- and space-resolved hard x-ray source was developed as a diagnostic tool for imaging underwater exploding wires. A ~4 ns width pulse of hard x-rays with energies of up to 100 keV was obtained from the discharge in a vacuum diode consisting of point-shaped tungsten electrodes. To improve contrast and image quality, an external pulsed magnetic field produced by Helmholtz coils was used. High resolution x-ray images of an underwater exploding wire were obtained using a sensitive x-ray CCD detector, and were compared to optical fast framing images. Future developments and application of this diagnostic technique are discussed.

Results of generation of extreme state of water in the vicinity of the implosion axis of converging strong cylindrical and spherical shock waves are reported. The shock wave was produced by underwater electrical explosion of cylindrical and spherical either Cu or Al wire arrays. A 10 kJ pulse generator with a current amplitude ≤ 500 kA and rise time of 350 ns was used to explode arrays with varying lengths, radii and number of wires. Hydrodynamic numerical simulations coupled with SESAME equation of state for water and the experimental data of the shock wave propagation, energy deposition rate to the array and light emission from the compressed water in the vicinity of the implosion axis were used to obtain the pressure, density and temperature profiles during the implosion. Dependences of the pressure in the vicinity of the implosion axes on the array radius and deposited linear energy density per unit length were obtained.

Sub-microsecond timescale underwater electrical wire explosions using Cu and Al materials have been conducted. Current and voltage waveforms and time-resolved streak images of the discharge channel, coupled to 1D magneto-hydrodynamic simulations, have been used to determine the electrical conductivity of the metals for the range of conditions between hot liquid metal and strongly coupled non-ideal plasma, in the temperature range of 10–60 KK. The results of these studies showed that the conductivity values obtained are typically lower than those corresponding to modern theoretical electrical conductivity models and provide a transition between the conductivity values obtained in microsecond time scale explosions and those obtained in nanosecond time scale wire explosions. In addition, the measured wire expansion shows good agreement with equation of state tables.

Experimental and simulation results of underwater electrical Cu, Al, and W wire explosions in the microsecond timescale are presented. It was shown that the electrical conductivity results for Cu and Al agree well with modified Lee-More and quantum molecular dynamic models for temperatures above 10 kK. The equation of state (EOS) values based on SESAME tables for Cu and Al were slightly modified for intermediate temperatures in order to obtain fitting between experimental and simulated exploding wire radial expansion. Also, it was shown that the electrical conductivity results and the EOS evaluation differ significantly from the results obtained in nanosecond timescale experiments. Finally, it was found that underwater electrical W wire explosion is characterized by the appearance of non-uniformities along the z-axis of the wire. This phenomena adds uncertainty to the possibility of applying this type of experiments for evaluation of the electrical conductivity and EOS of W.

XUV radiation from nitrogen filled capillary discharge plasma was diagnosed using a 10(4) grooves/mm SiNx free-standing transmission grating. The resolution bandwidth of 0.3 nm was achieved. Time dependence of 13.4 nm line emitted power was recorded by photomultiplier in order to verify inherence of resonant radiation emission corresponding to NVII 2-3 laser transition. An increase of emitted power is expected during the pinch decay caused by recombination processes. We report here results obtained with 90 mm long capillary discharge supplied by a current pulse with maximum amplitude of 50kA and quarter-period of 80 ns. This high-current pulse was generated by a 1.5 ohm water line high-voltage generator which is used for underwater wire explosion experiments and which was adjusted for capillary discharge design using results of PSPICE simulations. Initial nitrogen pressures were varied in the range of 20 divided by 500 Pa. MHD and kinetic simulations of the discharge plasma were performed and compared with experimental data. Simulations were performed with presumption of wall ablation. The capillary wall and electrodes material emission lines were also identified in measured spectra.

Summary form only given. Underwater electrical explosion of copper, aluminum and tungsten wires was used to study transport parameters for a wide range of temperatures and densities. Experiments have been carried out using two pulsed generators operating in microsecond and nanosecond time scales. For microsecond timescale, a generator with stored energy of ~6kJ and ~1μs rise time of ~300kA maximal amplitude current was used. For nanosecond timescale, a ~0.5kJ water forming line generator was used to produce a ~60ns rise time pulse with current of ~60kA. Application of these high-current pulses resulted in fast phase transition of the exploding wires and formation of dense, non-ideal plasma. The plasma was characterized using electrical probes, fast framing and streak images. From the experiments and through 1-D MHD simulations, the electrical conductivity of the plasma was obtained for densities in the range of 0.01-20 g/cm3 and temperatures of 0-8 eV. The experimentally obtained conductivity is compared to conductivity calculated using different models describing the matter in the warm, dense state. In addition, the equations of state of the matter have been evaluated from experimental results and compared to equation of state data from SESAME tables.

Summary form only given. We report on experimental and computer modeling research of underwater electrical wire explosions (UEWE) which present a promising method tor generation of strong shock waves (SSW) and non-ideal plasma. Micro-and nano-second time scale generators for UEWE of Al, Cu and W wires were employed. A mus (6 kJ stored energy, current of 80 kA, rise time of 2.5 mus) and ns (400J stored energy, current of 100 kA, rise time of 50 ns) generators were used in mus and ns time scale experiments, respectively. Different time-and space-resolved electrical, optical and spectroscopic diagnostics were used to study parameters of expanding discharge channel and generated SSW. Obtained scaling laws for explosion parameters suggest that the increase in the discharge power rate leads to an increase in the generated pressure amplitudes. Furthermore, increasing the power rate allows for an extremely high energy deposition, namely up to 200 eV/atom was registered in ns Cu UEWE. The high value of the energy deposition is due to the absence of shunting plasma shell which presents in vacuum electrical wire explosions. It was shown that up to 15% of the stored energy is converted top the energy of the SSW. In order to amplify the pressures generated by the exploding wires, accumulation effect in imploding cylindrical wire arrays was implied. High pressures of converging SSW up to 0.2 Mbar were registered near the array axis. Results of a simplified model indicate that, using a spherical geometry setup with 7.5 mm external radius of the water layer and ~35 kJ total deposited energy, 1.5-10 14 neutron yield during ~1.5 ns time can be achieved. These re suits suggest that ignition of DT target by implosion in water medium can be considered as a promising method for inertial confinement fusion.

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.