Generation of negative hydrogen ions in low voltage caesium-hydrogen discharge

Interest in low voltage Cs-H2 discharge is stimulated by the prospect of utilizing it as a source of H- ions. The authors discuss the results of theoretical and experimental investigations of the discharge. The plasma is created by means of Cs ionization, and H- generation is due to dissociative attachment of heated thermal electrons to vibrationally excited H2(X' Sigma g+,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 H2 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.