Influence of high energy electrons on negative ion density in a hot cathode discharge

This study investigates the influence of high energy electrons on the negative ion density along with the effect of filament current, discharge voltage, pressure, and magnetic filter field strength by carrying out measurements of negative ion density in a hot cathode discharge system in the double plasma device using a Langmuir probe technique. In the volume production technique, negative ions are formed by the dissociative attachment of low energy electrons to metastable hydrogen molecules and among the negative ion loss mechanisms; the presence of high energy electrons in the plasma is one of the important factors. Although the magnetic filter could reduce the temperature of the electrons in the target region considerably, high energy electrons were still present in the diffusion region, which could reduce the negative ion density. Negative hydrogen ion density measured by using Langmuir probe in the target region is also compared with the particle balance model considering the set of reactions involved in the production and destruction of negative ions, and a reasonably good match between them has been observed.