A dc negative ion facility has been built to study both the mechanisms controlling H−production in multipole volume sources and the design of accelerators for negative ion beams. After a 7.5‐cm movement of the extraction aperture position within the ion source, the arc current and source gas pressure were optimized, and an H−current of 10 mA was extracted from a 0.5‐cm2circular aperture in a 30‐s pulse from a 100‐A, 90‐V discharge run at 18.8 mT. This is the first operation of such sources to provide a quasi‐dc current of 20 mA cm−2. The installation of an octupole electron trap in the beam forming electrode has lowered the electron current extracted simultaneously with the H−beam by approximately a factor of 4, and this has led to a low H−beam divergence. The application of a small bias voltage of up to 2 V between the beam forming electrode and the anode has reduced this electron current still further (by more than a factor of 10) while maintaining the extracted ion current. It is now possible to extract ion currents from such a source/accelerator configuration that are larger than the accompanying electron current.