Kinetische Diagnose des Helium-Niederdruckfunkens

In a short spark discharge (energy release time < 0,5 μs) at pressures between 10 and 100 Torr a pure helium plasma was created and investigated by spectroscopic techniques. The following time dependent plasma parameters could be determined (0,5 ≦ t ≦ 5 μs): pressure p from hydrodynamic considerations, electron density n_e from the line profiles and gas temperature T_g from the Boltzmann population of the higher levels, i ≧. The population densities of the levels 3 and 4 deviated from the Boltzmann-T_g-straight line and thus indicated a strong disturbance of thermal equilibrium. For the determination of the electron temperature T_e an ionization rate equation was formulated, which took into consideration electron impact ionization, three body recombination and radiation recombination. The deviation from thermal equilibrium of the spark plasma was nearly constant in the investigated pressure-time region: the ratio T_g/T_e gave ≈ 0,06; the ration n_e/n_o was about 7 orders of magnitude below the corresponding Saha ratio.