|Ph.D Student||Yanuka David|
|Subject||Generation of Strong Converging Shock Waves by Underwater|
Electrical Explosion of a Wire Array
|Department||Department of Physics||Supervisor||Professor Yakov Krasik|
|Full Thesis text|
Research of warm dense matter and high energy density matter characterized by high values of temperature, pressure and density, attracts much attention due to its importance for confinement fusion, astrophysical problems, studies of equations of state and conductivity models at extreme parameters. In earlier research, carried out in the Plasma Laboratory, Physics Department, Technion, it was shown that underwater electrical explosions of a single wire and a wire array can be applied for the formation of such extreme states of matter. In addition, the explosions of cylindrical and spherical wire arrays are accompanied by the generation of converging strong shock waves which implosion leads to extremely high values of pressure, density and temperature of the water in the vicinity of the shock wave implosion axis or origin.
This PhD thesis considers experimental and numerical research of underwater electrical explosions of wire arrays for the generation of strong converging shock waves in a super-spherical geometry which could allow one to obtain superior parameters of water in the vicinity of the shock wave implosion origin. In addition, super-strong pulsed magnetic field generation experiments using a high-current discharge through a coil immersed in water were carried out. Pulsed power generators with stored energies in the range 0.4-6 kJ, current amplitude in the range 40 - 600 kA and operating in nanosecond - microsecond timescales were used for the electrical wire explosions and the magnetic field generation. Different types of electrical, optical, and spectroscopic diagnostics were applied to determine the parameters of the wires and generated shock waves. The spectroscopic measurements were the first attempt to directly measure the “water” plasma parameters in the vicinity of implosion as opposed to non-direct methods used in earlier research.
1D and 2D hydrodynamic simulations coupled with equations of state for copper and water were carried out for the determination of the parameters of water in the vicinity of implosion of the shock wave.
To realize a super-spherical geometry of the shock wave convergence, different wire arrays and boundary geometries were designed and applied in the experiments. These included spherical wire arrays, planar wire arrays above straight and parabolic walls in contact with each other, and cylindrical wire arrays with conical and parabolic walls placed inside the wire array.
The time- and space-resolved spectroscopic measurements of compressed and heated water in the vicinity of implosion resulting from the converging shock wave generated by an underwater explosion of a spherical wire array showed that the temperature of water exceeds 1 eV. The measurements were both fitted to a Planckian distribution assuming uniform thermodynamic parameters, and a more accurate calculation was made using the radiative transfer equation.
Strong pulsed magnetic fields were generated in non-destructive methods using single-, double-, and triple-turn stainless steel and copper coils. The magnetic fields up to 60 T were generated by passing a high current pulse through the coils which were immersed in water. The fields were measured using the non-disturbing method of Faraday rotation.