Comparison of time-resolved H-density measurements in a hydrogen discharge and model calculations

Time-resolved mass spectrometry of negative ions and time-resolved Langmuir probe measurements are carried out in a pulsed hydrogen discharge. Both diagnostics show a strong increase of the H - density in the post-discharge. The measured transient shape of the H - density in the hydrogen post-discharge is compared with an advanced theoretical model. This comparison shows that the H - slope is mainly influenced by the density distribution of vibrationally excited molecules and the transient drop of the electron temperature in the post-discharge. In accordance with our model, no influence of positive ions and atomic hydrogen on the H - density is observed up to plasma densities of 10 11 cm -3 . Measurements of the maximum H - density in the post-discharge in dependence on the duration of the single pulse indicate the density evolution of vibrationally excited molecules during the discharge. At plasma densities between 10 10 and 10 11 cm -3 a saturation of the density distribution of the vibrationally excited molecules is observed after 200-500 mu s. By variation of the pause duration with a fixed short discharge pulse (40 mu s) the lifetime of the vibrational excited molecules in the post-discharge is found to be approximately 1-4 ms.