[en] H/sup /minus// and D/sup /minus// ions have useful applications in high-energy accelerators and in neutral beam heating, or for current drive of fusion plasmas. Among the different techniques for producing H/sup /minus// ions, direct extraction from a hydrogen discharge is the most attractive. This method requires no cesium and the H/sup /minus// ions generated by volume processes have lower average energy than those formed by surface conversion or by charge exchange processes. For this reason, intensive research and development of volume H/sup /minus// sources are now being conducted at various accelerator and fusion laboratories