טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSheftman Daniel
SubjectElectrical Conductivity and Equations of State Metals at
Extreme Conditions and Fast Processes
DepartmentDepartment of Physics
Supervisors Professor Yakov Krasik
Professor Emeritus Joshua Felsteiner
Full Thesis textFull thesis text - English Version


Abstract

  The research presented in this thesis addresses the physical properties of warm, dense, non-ideal plasma generated through underwater electrical explosion of Copper, Aluminum and Tungsten wires. Pulsed power generators with current amplitudes of 30-300kA and rise times of 60-1200 nanoseconds were used to generate the warm, dense matter through the explosion process. The main aim of this research was to study the electrical conductivity and equations of state (EOS) of non-ideal plasma at the extreme conditions (pressure, density and temperature) obtained during underwater electrical explosions. Through the use of visible range spectroscopy it was found that the temperature of the surface and interior of the wire material cannot be measured due to the formation of a thin, dense column of plasma generated in the water adjacent to the wire-water boundary. The electrical conductivity and equations of state of the tested materials were studied through electrical waveform measurements and fast framing and streak photography of the exploding wires. In addition, a 1D magneto-hydrodynamic simulation was used to recreate the explosion process and complement the experimental data. Through matching between experimental and simulated results of current and voltage waveforms and wire expansion, the values of the electrical conductivity and EOS were found. The latter values were compared to theoretical models of conductivity and tabulated EOS data. It was found that at slower explosions (microsecond timescale) the experimental results of electrical conductivity and EOS fit well with modern conductivity models and tabulated EOS data, respectively. However, at faster explosions (nanosecond timescale) a large deviation between the experimental and theoretical values of conductivity and EOS was found. Several possible sources to this deviation are suggested: fast superheating of the wire material, uncertainty in the values of the ionic contribution to the tabulated EOS data and uncertainty in the ionization degree of the material at the physical conditions present during the explosion, which could affect the electronic contribution to the EOS. A Time- and space- resolved hard x-ray source was used to obtain x-ray images of an exploding wire. It was shown through comparison to optical self-light images that the radius of the wire was accurately measured from x-ray imaging. Modification and improvement of the x-ray source is planned in order to achieve high resolution radial profiles of the exploding wire and to detect possible instability occurrence.