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Evaluations of various sources for accelerator use at proton currents above 10 ma indicate that a variation of Von Ardenne's Duo Plasmatron will give performance superior to that of any other source presently available. Operating characteristics for various sizes of the source have been examined for H1+, H2+, H3+, H1−, He+, and He++ ions and electrons. Experience with protons in the current range from 1 to 30 ma indicates that the Duo Plasmatron can deliver up to 100 amp/cm2 of exit aperture area. Current densities such as this cannot be maintained in the accelerator-extractor section because of space charge forces, even at the highest gradients normally available for well-polished electrodes in vacuum; thus it can be said that proton current densities will be space-charge-limited by the accelerator rather than emission-limited by the source. Operation for He+ ions and electrons is similar to proton operation. Currents of 11 μa of H1− ions and 5 μa of He++ ions were extracted directly from a source which had been designed for a proton current of several milliamperes. The most striking features of the Duo Plasmatron are its remarkably high brilliance, high gas efficiency, good power economy, and compactness.