A parametric study was made of the pulsed hollow discharge duoplasmatron, operating as a negative hydrogen ion source in the pure hydrogen mode and in the mixed hydrogen–cesium mode. Effects of the arc current, gas pressure, and the magnetic field on the extracted H−current were investigated for different electrode geometries and potentials. In the hydrogen mode a maximum H−beam current of 11 mA was obtained from an anode extraction aperture of 2.45‐mm diameter, with a normalized emittance of 0.1&pgr; cm mrad. In the mixed hydrogen–cesium mode an H−beam current of 60 mA was obtained from the same aperture. At a current of 40 mA the normalized emittance was 0.23&pgr; cm mrad. An analysis of the results points to the volume production of H−ions in the hydrogen mode and to the surface production in the hydrogen–cesium mode.