Space-charge effects in the catcher gas cell of a rf ion guide

Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities