Publications
Modeling electrode plasma effects in particle-in-cell simulation of high power devices
A new method for including electrode plasma effects in particle-in-cell simulation of high power devices is presented. It is not possible to resolve the plasma Debye length, {lambda}{sub D} {approx} 1 {mu}m, but using an explicit, second-order, energy-conserving particle pusher avoids numerical heating at large {delta}x/{lambda}{sub D} >> 1. Non-physical plasma oscillations are mitigated with Coulomb collisions and a damped particle pusher. A series of 1-D simulations show how plasma expansion varies with cell size. This reveals another important scale length, {lambda}{sub E} = T/(eE), where E is the normal electric field in the first vacuum cell in front of the plasma, and T is the plasma temperature. For {delta}x/{lambda}{sub E} < {approx}1, smooth, physical plasma expansion is observed. However, if {delta}x/{lambda}{sub E} >> 1, the plasma 'expands' in abrupt steps, driven by a numerical instability. For parameters of interest, {lambda}{sub E} << 100 {mu}m. It is not feasible to use cell sizes small enough to avoid this instability in large 3-D simulations.