BASIC PROCESSES OF NEGATIVE HYDROGEN-ION PRODUCTION AND DESTRUCTION IN SOURCES AND BEAMS

This article contains the discussion of new discoveries and ideas rele vant to volume H- ion sources and beams. Recent research in laser irra diated H-2 by Pinnaduwage and Christophorou has shown that the rates o f dissociative attachment are strongly dependent on electronic excitat ion involving superexcited states and possibly Rydberg states. The obs ervation of anomalous attenuation of a 15 keV H- beam in a hydrogen ga s 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+, H-0, and electron beams produced by primary stri pping. The results of the investigation by electrostatic probes and by photodetachment of the properties of a hydrogen/deuterium multicusp i on source plasma when seeded with cesium vapor are reported. We found that the negative ion/electron density ratio is enhanced by cesium see ding, particularly at low pressure (a factor of 4 at 1 mTorr), while b oth the electron temperature and the electron density are reduced. (C) 1996 American Institute of Physics.