A duoplasmatron has been constructed specifically to produce negative ion beams of less than 5 keV energy. Design parameters are given for construction and operation of the source. Ion beam energy analyses indicate an energy full width at half maximum of less than 10 eV, and when the ion beam energy is extrapolated to zero, a full width at half maximum of 3 eV is observed. Ion beams of H−, O−, OH−, F−, CN−, and NO2−were produced at 2 keV with beam intensities between 3×10−7and 10×10−7A, measured behind a 0.63 cm diam aperture 140 cm downstream from the source.