The density of negative ions in a low-pressure hydrogen plasma has been investigated as a function of neutral gas pressure, plasma density, and electron temperature. The comparison of the experimental data, obtained by the photodetachment technique, with theoretical results derived from computed reaction rates, seems to indicate that hydrogen negative-ion production occurs mainly through the process of electron attachment on vibrationally excited hydrogen molecules.

The temperature dependence of the electrical conductivity and of the Seebeck coefficient of NiO samples with various Ni3+ concentrations is determined. These samples are obtained from a nickel salt, using various decomposition temperatures. The temperature dependence of the hole concentration, pα, is calculated from the Seebeck coefficient. Since pα is constant up to about 500 °K, the exponential temperature variation of the conductivity must be attributed to the temperature dependence of the mobility. It seems, therefore, that at least up to the Néel temperature non‐stoichiometric NiO exhibits a similar conduction mechanism to Li‐doped NiO, with holes hopping between Ni2+‐ions. The discrepancies between the values of the hole concentration determined from the Seebeck coefficient and those given by the chemical analysis are discussed in terms of a simplified model, taking into account the non‐uniform distribution of the excess‐oxygen atoms throughout the volume of the NiO grains. The results confirm that for NiO samples of high excess oxygen content the electrical conduction is mainly due to grain boundaries.

The density of negative hydrogen ions and the plasma characteristics are investigated as a function of the discharge current and the neutral gas pressure for several configurations of the magnetic multi pole, and in the absence of magnetic containment fields. It is shown that the hybrid magnetic multi pole configurations, characterized by a relatively low lifetime for wall losses of prim~~y electrons (10-7 s) contain high relative densities (10%-50%) of negative ions. The transition from the low density to the high density regime has been observed.

The results of an investigation on the extraction of volume-produced H -ions from severa] plasma sources, characterized by different magnetic multicusp configurations, as well as from a plasma source with no magnetic containment field, are presented. In all these configurations the extracted negative ion current can be increased and the electron current reduced by a suitable choice of the plasma electrode area and positive bias and of the extraction aperture area. This indicates that the variation of the extracted negati ve ion current due to the plasma electrode bias is an electrostatic effect. A significant effect of the plasma electrode bias upon the electron density and temperature is only observed in the neighborhood of the plasma electrode, while in the plasma center the negative ion and electron density are unaffected.