Relevance of Volume and Surface Plasma Generation of Negative Ions in Gas Discharges

Abstract

The relative contribution of volume and surface-plasma generation of extracted Нions in gas discharge sources is analyzed. By present time, it is well known that surface-plasma generation of extracted Нion is dominate above volume processes in discharges with admixture of cesium or others catalysts with low ionization potential. From the analysis presented below, it follows that contrary to the standard opinion repeated in tens of publications, in the optimized discharge sources without cesium and small currents of accompanying electrons, named by authors as "pure volume sources", a surface-plasma generation of extracted Нion also dominate above volume processes. For the effective generation of Нion beams in discharge without cesium, it is necessary to optimize surface-plasma generation of extracted Н-, Dion that, as a rule, leads to suppression of volume production. Such optimization allows considerably improving characteristics of Н-, Dsources for accelerators and for neutral beam injectors in magnetic confinement fusion.

Vibrational kinetics, electron dynamics and elementary processes in H2and D2plasmas for negative ion production: modelling aspects

“…Moreover, in addition to the Padua presentation, we will add a section dedicated to the elementary processes promoted by caesium in the so-called surface sources. Present negative ion sources (arc and rf) in fact achieve ITER relevant current densities of negative ions only by optimizing the surface formation which produces negative ion yields several times higher than the volume mechanism [5].…”