VUV emission spectroscopy combined with H− density measurements in the ion source Prometheus I

Abstract

“Prometheus I” is a volume H− negative ion source, driven by a network of dipolar electron cyclotron resonance (ECR; 2.45 GHz) modules. The vacuum-ultraviolet (VUV) emission spectrum of low-temperature hydrogen plasmas may be related to molecular and atomic processes involved directly or indirectly in the production of negative ions. In this work, VUV spectroscopy has been performed in the above source, Prometheus I, both in the ECR zones and the bulk (far from ECR zones and surfaces) plasma. The acquired VUV spectra are correlated with the negative ion densities, as measured by means of laser photodetachment, and the possible mechanisms of negative ion production are considered. The well-established H− formation process of dissociative attachment to vibrationally excited molecules is evaluated, while an additional production path (i.e. neutral resonant ionization) is tested due to the recently attracted interest. The obtained results indicate that for the source Prometheus I, the dominant formation process is dissociative attachment.