Spectroscopic measurements of neutral hydrogen level populations in a multipole plasma H-source

Abstract
Both active and passive spectroscopic techniques have been used to investigate the excited state populations in a multiple hydrogen plasma device typical of those under development for negative ion production. Laser fluorescence measurements have been used to obtain the hydrogen n=2 level population directly, and a simple model of the relevant atomic and molecular processes has been used to estimate from this the total atomic density. The density obtained is sufficiently high that lowering of the obtainable H- density by atomic processes cannot be ruled out. Measurements of emitted visible line radiation have demonstrated the existence of a strong atomic spectrum originating from close to the extraction aperture of the source. This may provide a spectroscopic method of measuring the H- density.

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