Hm. Katsch et al., COMPARISON OF TIME-RESOLVED H- DENSITY-MEASUREMENTS IN A HYDROGEN DISCHARGE AND MODEL-CALCULATIONS, Journal of physics. D, Applied physics, 28(3), 1995, pp. 493-499
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.