Energy transfer and its effects on laser-plasma instability PIC simulations using variable charge weights*

Using variable charge weights to represent density variations in Particle-in-Cell (PIC) simulations can maintain good statistics while being computation efficient and is a common practice. But how energy transfer between different charge weights affects simulation results has not been systematically studied. We developed a methodology of quantitatively comparing PIC simulations with variable and constant charge weights, by performing a simulation multiple times to separate random fluctuations from the actual effects. We apply the methodology on a PIC simulation of laser-plasma instabilities (LPI) in shock ignition where the density varies from 0.016 to 0.4 n_c (n_c the critical density). The variable- and constant-charge-weight runs, their computation loads differing by 6 times, were repeated 20 times and a series of important quantities such as laser reflectivities, plasma wave amplitudes, electron temperatures and hot electron generation were compared. Overall we found no physically significant differences but statistically significant difference did exist.