Digital computer simulation of three-dimensional ion beam extraction and transport systems

SNOW, a program for the simulation of ion beam extraction from plasmas, has been extended into three dimensions. Basic relaxation techniques are employed, alternately solving for voltages (using Poisson´s equation expanded in difference form) and computing trajectories through the device. Electrodes are laid out on a large three-dimensional array for the simulation of voltages. The plasma is simulated on a second array (that may be finer than the voltage matrix) by using a background (Boltzmann) electron distribution balanced with the ion space-charge density at the injection plane. The plasma is determined by its electron temperature and the ion drift energy and spatial distribution. The program automatically determines the shape and location of the plasma surface. It is written in generic FORTRAN 77 and can be run on virtually any computer.<>