NEGATIVE-ION VOLUME PRODUCTION-MODEL - STATE OF THE EXPERIMENTAL CONFIRMATION

We report the results of simulating two multicusp volume negative ion sources in which plasma parameters, hydrogen vibrational spectra, and in one case the negative ion density, have been measured. We find gene rally good quantitative and qualitative agreement between experiment a nd theory for the basic discharge parameters. Good agreement is also f ound for atomic density, although the wall recombination coefficient g amma(H) is 0.05 in one source and 0.5 in the other. The calculated den sities of vibrationally excited states with upsilon'' greater-than-or- equal-to 5 are higher than the measured densities, but the calculated negative ion densities are lower than available measurements. Possible causes for these discrepancies are suggested. Fundamental modificatio ns to the model may be necessary, and we have discussed two possibilit ies: a suprathermal rotational spectrum, and a spatial gradient in vib rational excitation (due to elastic collisions which can localize the effect of vibrational wall cooling near the wall).