Extending the binary collision algorithm to non-Spitzer systems and application to laser heating and damage

Abstract

We have generalized the Nanbu collision algorithm to accommodate arbitrary collision rates, enabling accurate kinetic modeling of short range particle interactions in non-Spitzer systems. With this extension, we explore the effect of different collision models on the simulation of how ultraintense lasers first begin to heat a target. The effect of collisions on plasma evolution is crucial for treating particle slowing, energy transport, and thermalization. The widely used Nanbu collision algorithm provides a fast and computationally efficient method to include the effects of collisions between charged particles in kinetic simulations without requiring that the particles already be in local thermal equilibrium. However, it is "hardwired" to use Spitzer collision rates appropriate for hot, relatively dilute plasmas. This restriction prevents the Nanbu collision algorithm from accurately describing the initial heating of a cold target, a key problem for the study of laser damage or the generation of the warm dense matter state. We describe our approach for modifying the Nanbu collision algorithm and demonstrate the improved accuracy for copper targets.

Ultrafast Laser Material Damage Simulation—A New Look at an Old Problem

“…We also neglect the Auger recombination, since the strong reduction of its rate with the increase of band gap [83] suggests that this process is not significant for the wide-band-gap dielectrics under consideration. Similar treatment can be found in the simulations by the PIC methods, but the "hard" collision component is introduced in the scattering parameter, and the regimes for different collision mechanisms are separated by a threshold velocity [84]. Nevertheless, Equation (15) does not take the electron-phonon or the electron-defect collisions into consideration [85].…”