Simple optics description of the plasma sheath and plasma electrode region

摘要

A simple model of the optics of an ion source has been developed and compared with the exact Poisson solution calculated by computer code SNOW. The model replaces the Poisson potential by a Laplacian potential that is calculated by replacing the plasma and plasma sheath by a planar plate. This Laplacian potential is then used with and without a linear space-charge correction to calculate particle trajectories. In this model the only free parameter is the distance between the planar plate and the plasma electrode. In general, there is good agreement between emittance curves calculated by the model and the SNOW results even when no space-charge correction is used. This implies for the geometry we studied, that the effects of the plasma sheath and non-linear space-charge forces are small compared to aberrations introduced by the plasma aperture.