EFFECTS OF THE ENERGY-DISTRIBUTION OF FAST ELECTRONS ON H-2 VIBRATIONAL-EXCITATION IN A TANDEM NEGATIVE-ION SOURCE

The population distribution of vibrationally excited hydrogen molecules H-2(upsilon"), and the H- production are investigated theoretically by solving numerically a set of particle balance equations in a steady-state pure hydrogen plasma. In particular, the enhancement of the H-2(upsilon") distribution is discussed for different energy distributions of fast electrons e(f). Whether the energy distribution for e(f) is a delta function type or a plateau type, collisional excitation of H-2(upsilon") caused by e(f) is very effective to enhance the H- production and a resultant vibrational distribution becomes the plateau distribution. Besides these, if e(f) with energies higher than 30-40 eV are present, both H-2(upsilon") excitation and then H- yield hardly depend on the form of the energy distribution of e(f).