**Figure 12.**

*Photograph from above a 350 mm broad vertical argon ribbon beam of 120 mA at 3 keV. The beam at left is emerging from the third electrode of the triode. Divergence is +/ 20 mrad. Scale is about 50%.*

suppression voltage can be adjusted to minimize this current, but then differential gas flow adjustments (made with the total beam current or arc current held constant) can be made to further reduce the unwanted suppression current, which is to effectively make the beam divergence—and hence its uniformity—more uniform. A second method, as discussed above, is to place a hot cathode at each end. If the ion source is well over 2 m long, it may be beneficial to add an additional hot cathode at a central location.
