Effect of emission aperture shape upon ion optics

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.