Modeling the electron collision frequency during solid-to-plasma transition of polystyrene ablator for direct-drive inertial confinement fusion applications

Abstract

Within the inertial confinement fusion (ICF) framework, the solid-to-plasma transition of the ablator arouses increasing interest, in particular due to the laser-imprint issue. Phase evolution of the ablator is linked to the evolution of the electron collision frequency, which is of crucial importance since it drives electron heating by laser energy absorption and lattice-ion heating due to collisions between electrons and the lattice-ion system. Thus, an accurate description of electron collisions over the whole temperature range occurring in ICF, starting from a few tens of kelvins (solid state) up to tens of millions of kelvins (plasma state), is necessary. In this work, a polystyrene ablator is considered, and a model of chemical fragmentation is presented to describe the heated polystyrene evolution. Electron collisions are described by electron–phonon collisions in the solid state and by electron–ion and electron–neutral collisions in the plasma state. An effective electron collision frequency valid over the whole range of temperatures reached in ICF experiments is established and discussed. Thermal conductivity is also deduced from collisions in the plasma state and shows a good agreement with the one evaluated by ab initio calculations.