|M.Sc Thesis||Department of Physics|
|Supervisors:||Prof. Krasik Yakov|
|Prof. Emeritus Felsteiner Joshua|
|Full Thesis text|
The subject of this research is the process of underwater electrical wire explosion (UEWE) accompanied by generation of strong shock waves (SSW) in the surrounding water. During this process, the metal wire material undergoes several phase transitions, namely melting, evaporation and the formation of plasma. These transformations occur during short time (10-7-10-5 seconds) and lead to rapid expansion of the wire in dense, impeding water, resulting in the conditions of extremely large pressure (≥109Pa) and relatively low temperature (of several eV). The metal plasma formed during this process is of the strongly coupled type, i.e., this plasma is characterized by a coupling parameter Γ>1. The physical conditions obtained during UEWE provide an opportunity to conduct basic physics research of transport parameters of different metals at the above mentioned extreme conditions. This research is related to space and planetary physics, and also proves to be a useful tool for the construction of new, or validation of existing equation of state (EOS) and conductivity models.
The main purpose of this thesis is investigation of the thermo-physical properties and electrical conductivity of metals during UEWE. A straightforward measurement of electrical conductivity of metal wire during UEWE is not possible because of electromagnetic noise, temperature and density gradients inside the wire, as well as wire and water plasma opacity. Therefore, the experimental data must be complemented by a numerical magneto-hydrodynamic (MHD) simulation, coupled to the equation-of-state (EOS) and conductivity data.
The experiments were carried out using a sub-microsecond high-current pulse generator, with stored energy of 4.7kJ and typical current rise time of 450ns. The maximum obtained current amplitude and the energy density deposition rate reached ~250kA and ~0.2eV/(atom?ns), respectively. Two types of diagnostics were employed, namely electrical measurements of the discharge current and voltage, and time- and space-resolved optical observations by shadow and direct imaging of the exploding wire. Explosions of Al, Cu and W wires were studied, with the wires having the same length but different diameters, which resulted in different values of deposited energy density and energy density deposition rates. The obtained waveforms of the discharge current and voltage, the trajectory of the strong shock wave and discharge channel expansions were compared with the results of MHD modeling coupled with EOS data base for the exploding materials and water.