The operating characteristics of an ion source of the type described by Kistemaker and Dekker are given. The dependence of the total ion output on the ion source pressure, magnetic field, anode voltage, filament emission, and probe voltage is described. When hydrogen gas was used the ion· source operated stably for pressures in the range of 1.5 to 2.5 microns of Hg producing maximum ion currents of 3 to 5 ma. Its gas consumption was relatively high (22.5 cc/hr, STP) and the proton percentage of the ion beam was of the order of 8%. The best focusing gave a beam diameter of 5 mm on a target 2 meters from the ion source. The filament lifetimes varied from 50 to more than 100 hours. The power consumption for ion beams of 3 ma or less was found to be about 0.15 watts/ua
