Numerical simulation of laser-produced plumes

Summary form only given. We have conducted numerical simulations of laser-produced plumes to model its generation and dynamics. In laser-ablation experiments, we can change the input heat flux into material by controlling laser intensities and pulse durations, and thus we can easily obtain conditions for a wide range of the density and temperature of ablated materials. In order to model generation of plumes, we have developed a radiation hydrodynamic simulation code. We will show the dependence of density and temperature of generated plumes on ablated material. The atomic number-Z dependence of the dynamics of expanding plumes results from different sound velocities and radiation energy losses in different Z material. We compared carbon (Z=6) and tungsten (Z=74), and investigated the profile of those plumes. We confirmed that the radiation energy loss affects the plume temperature and density. Also, we simulated dynamics in rarefied gas such as the plume expanded into vacuum from the wall. The conventional hydrodynamic equations deal with highly dense plasma or gas. However, the approach is not valid for expanded low density plasma or gas. Therefore, we have developed a Direct Simulation Monte-Carlo code (DSMC). The initial conditions of the plumes in DSMC are calculated using the hydrodynamic code. We will present the initial conditions and successive DSMC simulation results of plume properties in a chamber, and demonstrate that changing the collision rate, we can observe transition of the dynamics from the collision-less plume dynamics to collisional one in the cases of carbon and tungsten plumes.