New concepts for the ion guide technique

Abstract

The technique of using noble gases to cool energetic beams offers fast extraction times, very little sensitivity to chemical properties of the ions and very low-energy spreads. A variant of this method is based on the selective laser ionization of radioactive species after they have been thermalized in gas as neutral atoms. The laser ion source in Jyväskylä is used to highlight the importance of buffer gas purity using yttrium, a particularly chemically reactive element. The time distribution profiles obtained on-line illustrate the competing factors that create and destroy the ion of interest during evacuation from the ion guide. A review of the extraction efficiencies of gas catchers of different volumes, buffer gases, projectile energies and electric fields all show a common decrease as a function of ionization-rate density. The reasons for this decline and possible solutions to tolerate higher primary beam intensities are discussed.