ION FOCUSING BY AN EXPANDING, 2-DIMENSIONAL PLASMA SHEATH

The temporal evolution of the collisionless, pulsed plasma sheath arou nd a square bar is studied using a two-dimensional particle-in-cell co de. It is found that the incident ion dose is peaked near to, but not on, the corner. This effect is explained physically by considering ion trajectories across the sheath, yielding an estimate for the dose in good agreement with the simulation results. The present results are co mpared to those from a fluid simulation [T. E. Sheridan and M. J. Alpo rt, Appl. Phys. Lett. 64, 1783 (1994)], and it is found that the fluid simulation erroneously underestimates the ion dose near the corner of the bar. (C) 1996 American Institute of Physics.