20 years of cesium catalysis for negative ion production in gas discharges (invited)

<jats:p>Cesium catalysis, considerable acceleration of negative ion production in a gas discharge by injecting a small admixture of cesium or other substances with low ionization potential (for example, the first or the second group elements), is used now very widely in ion sources. The cesium injection turns on the catalysis of negative ion production on the electrodes surface, bombarded by particles from discharge plasma. The cesium adsorption significantly increases the probability of the electron capture from the electrode surface to the electron affinity levels of sputtered and reflected particles by decreasing the surface work function from 4–5 eV up to 1.5 eV. It increases considerably negative ion containment in particle flux from the surface. Ion sources using cesium catalysis have been named surface plasma sources (SPS), because for their operation a strong interaction of gas discharge plasma with a surface is very important. However, volume negative ion production depends on cesium admixture and surface processes also. Highly efficient cesium catalysis has been discovered in Novosibirsk Institute of Nuclear Physics on July 1, 1971. During 20 years in many laboratories around the world wide investigations of physics processes in surface-plasma sources have been executed. Various types of SPS, optimized for different applications in accelerators, in plasma physics and thermonuclear research, in technology, have been developed. The distinctive features of physical processes in SPS and technological development for high efficient SPS operation are reviewed in presented papers.</jats:p>