Correlation of H- density and work function of a plasma electrode in H2+alkali (Rb, Cs) plasma

The work function of the plasma electrode of an H^- ion source was measured photoelectrically in H² plasma, which contains vapor of an alkali metal. The measured work function was correlated with the H^- density obtained by a laser photodetachment technique. As the work function of the plasma electrode was reduced due to rubidium injection, the ratio of H^- density to electron density, n/n_e increased gradually. The n/n_e ratio became maximum when the work function reached the minimum value. The same result was obtained in the case of cesium injection