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.

Interest in low voltageCs-H2 discharge is stimulated by the prospect of utilizing it as a source of H-ions. In this paper we discuss the results of created by means of Cs ionization, and H-generation is due to dissociative attachment of heated thermal electrons to vibrationally excited H2(X'E9+, v ) levels. Two modes of the discharge are analysed: the discharge in dense hydrogen plasma, where both electron-vibration and vibration-vibration pumpings of excited HP levels are important, and Knudsen discharge, where the high vibrational level population is due to the electron-vibration exchange alone. The dependence of H-concentration on the discharge characteristics and the optimum parameters for H-generation are discussed. A self-consistent theory of the discharge is presented. The results of the first experimental investigation of a low voltage Cs-H2 discharge are given. It is shown that there is good agreement between the experimental and theoretical plasma parameters and that the optimum parameters for H-generation may be achieved in an experimental device.

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