Effects of the energy distribution of fast electrons on H2 vibrational excitation in a tandem negative ion source

The population distribution of vibrationally excited hydrogen molecules H2(v″), 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 H2(v″) distribution is discussed for different energy distributions of fast electrons ef. Whether the energy distribution for ef is a delta function type or a plateau type, collisional excitation of H2(v″) caused by ef is very effective to enhance the H− production and a resultant vibrational distribution becomes the plateau distribution. Besides these, if ef with energies higher than 30–40 eV are present, both H2(v″) excitation and then H− yield hardly depend on the form of the energy distribution of ef.