H−ions formed by volume processes have been extracted from a multicusp ion source. It is shown that a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H−ions available for extraction. A further reduction in electron current is achieved by installing a pair of small magnets at the extraction aperture. An H−ion current density of 38 mA/cm2was obtained with a discharge current of approximately 350 A. Different techniques to increase the H−ion yield have also been investigated.