Production of a Li− ion beam from a thermal contact–ionization plasma source

Abstract

The beam source is composed of a thermal contact–ionization plasma source and an accelerating lens system. The plasma source is made of a rhenium-foil cylinder 5 mm in diameter and it can be heated up to about 3000 K. A Li+ beam current over 500 μA has been obtained with this source. For the production of a Li− beam, an additional reservoir is attached to the source to supply Cs vapor into the plasma. The ion species can be examined by the time-of-flight (TOF) technique. In the case of Li+ production, ions of alkaline impurities, Na and K, in the Li metal have been observed in the TOF spectra. In the case of Li− ion production, the current intensity of negative ions also changes with the passage of operating time from K−, Na− to H− or H−2. This is also attributable to alkaline impurities in Li metal. A negative ion beam, which has been observed after the evaporation of impurities amounting to 200 nA, is very likely attributable to the Li− beam, though the corresponding TOF signal is very noisy.