COMPARISON OF TIME-RESOLVED H- DENSITY-MEASUREMENTS IN A HYDROGEN DISCHARGE AND MODEL-CALCULATIONS

Time-resolved mass spectrometry of negative ions and time-resolved Lan gmuir probe measurements are carried out in a pulsed hydrogen discharg e. Both diagnostics show a strong increase of the H- density in the po st-discharge. The measured transient shape of the H- density in the hy drogen post-discharge is compared with an advanced theoretical model. This comparison shows that the H- slope is mainly influenced by the de nsity distribution of vibrationally excited molecules and the transien t drop of the electron temperature in the post-discharge. In accordanc e 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). M easurements of the maximum H- density in the post-discharge in depende nce on the duration of the single pulse indicate the density evolution of vibrationally excited molecules during the discharge. At plasma de nsities between 10(10) and 10(11) cm(-3) a saturation of the density d istribution of the vibrationally excited molecules is observed after 2 00-500 mu s. By variation of the pause duration with a fixed short dis charge pulse (40 mu s) the lifetime of the vibrational excited molecul es in the post-discharge is found to be approximately 1-4 ms.