Numerical methods for particle simulations at extreme densities and temperatures: Weighted particles, relativistic collisions and reduced currents

We present a fully relativistic energy-conserving binary collision model for particle simulations with large density scale plasmas. Our model deals with collisions between weighted particles of arbitrary species, conserving energy perfectly in each collision while momentum is conserved on the average. We also discuss a new method to model extremely high densities, applicable to a wide range of plasmas from the cold, non-relativistic to the ultra-relativistic regime in the high energy density physics.