Basic processes of negative hydrogen ion production and destruction in sources and beams (invited)

This article contains the discussion of new discoveries and ideas relevant to volume H- ion sources and beams. Recent research in laser irradiated H2 by Pinnaduwage and Christophorou has shown that the rates of dissociative attachment are strongly dependent on electronic excitation involving superexcited states and possibly Rydberg states. The observation of anomalous attenuation of a 15 keV H- beam in a hydrogen gas target led us to consider the possibility of secondary H- stripping processes, related to low-energy interactions between primary H- ions and the secondary H+, H0, and electron beams produced by primary stripping. The results of the investigation by electrostatic probes and by photodetachment of the properties of a hydrogen/deuterium multicusp ion source plasma when seeded with cesium vapor are reported. We found that the negative ion/electron density ratio is enhanced by cesium seeding, particularly at low pressure (a factor of 4 at 1 mTorr), while both the electron temperature and the electron density are reduced. copyright 1996 American Institute of Physics