Use of Axially Symmetric Electrostatic Fields for Ion Beam Focussing

The l/r electric field obtained between charged coaxial cylindrical electrodes is useful for focussing hollow ion beams in ion microprobe and ion implantation applications. The focussing strengths are mass independent at nonrelativistic energies. Focussed particle densities can be enhanced by using a diverging-converging pair to flatten the dependence of focal length on incoming beam radius. Transport of 425 keV and 1 MeV protons has been simulated and results are presented.