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 for shock wave characterization. A satisfactory agreement was found between the results obtained by these methods.
A brief review of the results obtained in recent research of underwater electrical wire explosions using microsecond and nanosecond generators is presented. It was shown that the increase in the rate of energy input into the exploding wire allows one to increase the wire temperature and amplitude of shock waves (SWs). Estimated energy deposition into Cu and Al wire material of up to 200 eV/atom was achieved. In microsecond time scale wire explosion, a good agreement was attained between the wire resistance calculated using the equation of state (EOS) and that obtained experimentally. Conversely, in nanosecond time scale wire explosion, the wire resistance of EOS was modified in order to fit experimental data. Analysis of the emitted radiation showed that black body approximation cannot be used to characterize exploding wire radiation. It was found that 24% of the deposited energy is transferred into the water flow's mechanical energy. Also, it was shown that converging SWs formed by the explosion of cylindrical wire arrays can be used to achieve a pressure up to 250 kbar at the axis of implosion. Hydrodynamic simulations showed that with the use of relatively moderate pulsed power generators with stored energy of several hundred kilojoules, a pressure of several megabar can be achieved at the axis of implosion.
The results of the characterization of large-scale RF plasma for studying nonlinear interaction with a high-power (∼400 MW) short duration (∼0.8 ns) microwave (∼10 GHz) beam are presented. The plasma was generated inside a Pyrex tube 80 cm in length and 25 cm in diameter filled by either Ar or He gas at a pressure in the range 1.3-13 Pa using a 2 MHz RF generator with a matching system and a quadruple antenna. Good matching was obtained between the plasma parameters, which were determined using different methods including a movable Langmuir probe, microwave cut-off, interferometry, and optical emission spectroscopy. It was shown that, depending on the gas pressure and RF power delivered to the antenna, the plasma density and electron temperature can be controlled in the range 1×10 10 -5×10 12 cm −3 and 1-3.5 eV, respectively. The plasma density was found to be uniform in terms of axial (∼60 cm) and radial (∼10 cm) dimensions. Further, it was also shown that the application of the quadruple antenna, with resonating capacitors inserted in its arms, decreases the capacitive coupling of the antenna and the plasma as well as the RF power loss along the antenna. These features make this plasma source suitable for microwave plasma wake field experiments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.