Absorbing boundaries for space plasma simulations

Summary form only given, as follows. For the simulation of plasma phenomena in infinite space, the computational domain must be surrounded by boundaries that absorb radiation. For spherical computational domains a rigorous absorbing condition can be formulated and implemented. This requires working in spherical polars and expanding surface data in spherical harmonics. A history of the past L steps must be kept for each Lth-order harmonic in order to predict its value at the next step. For Cartesian meshes and box-shaped boundaries, E.C. Lindman´s method (J. Comput. Phys., vol.18, p.66, 1975) can be applied on each of the six surfaces. However, it is arithmetic-intensive and it still leaves problems in the eight corners. Opting for the lowest order Lindman scheme and restricting angles of incidence to less than 45 degrees from vertical achieves albedos lower than 0.00003. Since finite-difference methods for Maxwell´s equations in vacuo are highly efficient, a wide buffer region can be allowed between radiating plasma sources and boundaries, thereby reducing angles of incidence. A simple PC program using the low-order method has demonstrated how an expanding wave is apparently fully absorbed at the boundaries.<>