A multiaperture ion source with adjustable optics to provide well-collimated, high-current-density, low- to medium-energy ion beams

The design, operation, and characterization of a new, adjustable-grid, multiaperture ion source are described. The capability for in situ relative lateral motion of the grids allows beam steering and alignment during source operation. The maximum beam deflection angle is ~ 10° at a beam acceleration voltage Vb = 1000 V. The grid separation distance dg is also adjustable in situ, allowing independent control over beam current and voltage while maintaining a minimum beam divergence. Decreases in beam divergence angle a, by as much as a factor of 3 over a comparable fixed-grid source, were obtained. Beam accelerating voltages Vbranging from 200 to 1000 V were investigated for dg values between 1 and 4 mm with a grid hole diameter of 2 mm. Minimum a values ranged from 4° to 7°. The total current density at minimum a for dg = 1 mm and Vb = 1000 V was 2.2 mA cm-2. The dependence of the measured beam divergence on source operating conditions and grid geometry is explained using a simple ion-optics model.