Studies of the hollow discharge duoplasmatron as a source of H− ions

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 0.1π 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 0.23π 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.