DYNAMIC AND SELECTIVE CONTROL OF THE NUMBER OF PARTICLES IN KINETIC PLASMA SIMULATIONS

An algorithm for the dynamic control of the number of particles in a p article-in-cell (PIC), plasma simulation is presented. The algorithm s electively splits and coalesces particles to control the number of par ticles in each grid cell. It is designed for multiple-length scale pro blems where an adaptive grid can be applied and for PIC simulations on parallel computers where a constant number of particles per cell is u seful for computational efficiency. The algorithm preserves the charge assignment at grid points while splitting one particle into two, or w hile coalescing two particles into one. Errors in momentum or energy c onservation are controlled by a simple, a priori test. The accuracy of the algorithm is demonstrated in several simulations in one dimension , including a collisionless slow-shock, where an adaptive grid calcula tion with dynamic number control gives comparable accuracy to a unifor mly zoned calculation without dynamic control with just 50% of the eff ort. (C) 1994 Academic Press, Inc.