Within an ion pump, accelerated ions leave the center portion of an anode tube due to the anode tube symmetry and the generally symmetrical electric fields present. The apparent symmetry within the anode tube may be altered by making the anode tube longitudinally segmented and applying independent voltages to each segment. The voltages on two adjacent segments may be time varying at different rates to achieve a rasterizing process. In various embodiments, one or more wire internal to the anode structure and having a time-varying electric potential may alter the trajectory of the ions leaving the anode tube, as may the shape of the anode near the ends of the anode tube.