simulation software

I am currently entertaining an idea for a science project that will use a system similar to chathod ray tubes in order to deposit a thin layer of coating on a metal surface. the system will generate a ray of posivite ions using UV light on vapour, which in turn will be accelerated by a static electrical field of charged plates. i want to find a way to experiment with different configurations using simulation software that is capable of calculating electric potential at any given point for a system of charged plates.

the advantage of this method as that it will allow the creation of a constant level of kinetic energy in the beam (just like CRT's do with electrons), rather then a multi stage, percicly calculated magnetic field like those used in particle accelerators.

can anyone advise?