Negative ion production for neutral (deuteron) beam injectors is considered for a general system utilizing charge-exchange production in alkali metals. Experimental results provide parameters and show good correlation with calculations using known atomic cross sections, so that beam behavior can be predicted. It is found that coupling into the high voltage accelerator poses significant constraints on optimization of the system, e.g., to determine its minimum size. A typical design for 200-ke V final energy provides D− at 1.5 keV from charge-exchange in rubidium, with an average current density of 23 mA/cm2 and a total current of 20 A.