An optimized tandem two‐chamber negative‐ion source system is discussed. In the first chamber high energy (E≳20 eV) electron collisions provided for H2vibrational excitation, while in the second chamber negative ions are formed by dissociative attachment. The gas density, electron density, and system scale length are varied as independent parameters. The extracted negative ion current density passes through a maximum as electron and gas densities are varied. This maximum scales inversely with system scale length, R. The optimum extracted current densities occur for electron densities near nR=1013electrons cm−2and for gas densities, N2R, in the range 1014to 1015molecules cm−2. The extracted current densities are sensitive to the atomic concentration in the discharge. The atomic concentration is parametrized by the wall recombination coefficient, &ggr;, and scale length, R. As &ggr; ranges from 0.1 to 1.0 and for system scale length of one centimeter, extracted current densities range from 8.0 to 80. mA cm−2.