Numerical simulation on volume production of negative ions in hydrogen plasmas, 2

Dependence of H- production on plasma parameters (i.e. electron density ne, electron temperature Te and hydrogen gas pressure p) is studied by using a set of particle balance equations in a steady state hydrogen plasma. The model includes six species of vibrationally excited hydrogen molecules H2*(vibrational level v'' = 5 - 10) which are important for H- production. Particular attention has also been paid to wall effects on H- production. So, both the wall recombination coefficient γ1 for H and the wall de-excitation collision parameter γ2 for H2*(v'') are treated as numerical parameters. With increasing Te, H- yield decreases. Both ne and p have some optimum values for H- production. The most significant point is that ion species ratios depend strongly not only on plasma parameters but also on wall parameters, i.e. γ1 and γ2. For H- production, the optimum condition is that γ1 ≅ 1 and γ2 << 1. (author)