Speaker
Description
Physical properties of a guiding cone for fast ignition in an inertial confinement fusion system are one of the key issues to understand the behavior of laser-generated fast electrons. The guiding cone will be changed from a solid state to a region of warm dense matter (WDM) irradiated by an intense-laser. The conversion efficiency, which is defined by the ratio of the energy of fast electrons to the heated implosion core, relies on the thermal and electrical conductivities of the cone. However, the thermal and electrical conductivities are not explained in WDM. To evaluate the behavior of fast electrons in the guiding cone, the thermal and electrical conductivities in WDM region are required.
To measure the thermal and electrical conductivities of fusion materials in WDM region, we have developed a simultaneous measurement method of both conductivities. The method is an isochoric heating using pulsed-power discharge with a ruby capillary. The electrical conductivity is estimated from the shape of WDM and the measured voltage-current waveform. The thermal conductivity is estimated by measurement of the thermal conduction from WDM to ruby capillary based on the temperature dependences with laser-induced ruby fluorescence. The WDM of gold was generated, and the temperature and density dependences of the thermal and electrical conductivities were measured. As a result, the electrical conductivity of WDM had about 4$\times 10^{4}$ to 9 $\times 10^{4}$ S/m with the temperature from 1.5$\times 10^{4}$ to 1.5$\times 10^{5}$ K. The electrical conductivity dependence on the temperature has an inflection point as a metal-non-metal transition.
