Effect of emission aperture shape upon ion optics

Abstract

Several different axisymmetric aperture shapes have been studied, experimentally and theoretically, for use in the plasma electrode employed in extracting ions from a plasma. Compared to a cylindrical bore aperture, a class of shapes opening away from the source plasma resulted in smaller beam divergence (due to reduced aberration fields), while a class opening toward the source plasma resulted in higher beam power density at optimum divergence. The minimum half-width-half-maximum divergence obtained for the former class was 0.57° at a beam energy of 27 kV, as compared to 1° obtained for a conventional cylindrical bore aperture.