Cylindrical expansion of a ultra-high density plasma for X-Ray laser source (1st report, effect of coulomb collisions)

Particle-in-cell simulation is carried out for the expansion of a multi-charged dense plasma for X-ray laser systems. All Coulomb collisions among charged particles are taken into consideration by using Nanbu's theory of Coulomb collisions [Phys. Rev. E 55 (1997) 4642], together with our recent extension to the case when the weight assigned to a simulated particle varies from particle to particle [Trans. Jpn. Soc. Mech. Eng. 64, B (1998), 2512]. The effect of Coulomb collisions on the expanding plasma is found to be very large, e. g. the splitting of temperature components during the expansion is largely reduced. The electron temperature is nearly spatially uniform, and it decreases with time. The charge neutrality condition is broken near the ion front, and the electric field reaches its peak at the ion front. In the expanding region, the ion density decreases exponentially with radius r, and the ion flow velocity increases linearly. These features of ions agree well with the self-similar hydrodynamic solution for the planar expansion.