Characterization of a cryogenic ion guide at IGISOL

A small volume cryogenic ion guide has been characterized at the IGISOL facility, Jyväskylä, as a prototype to verify whether there are any major obstacles to the use of high-density cryogenic helium gas for the stopping and extraction of high-energy ions from a large volume cryogenic ion catcher. The expected temperature scaling of the mass flow through the ion guide has been confirmed, showing that for the same helium density, the differential pumping requirements are less stringent for cryogenic operation. At 90K a clear reduction in the mass-analyzed impurities is achieved, although lower temperatures are required to freeze out oxygen and nitrogen. This is supported by the reduction in the measured secondary beam current exiting the ion guide in the presence of primary beam. Despite this reduction, the activity of 20Na (t1/2=446ms) at primary beam intensities above 1μA is rather similar to that achieved at room temperature. A constant extraction efficiency of a beam of 58Ni+ ions, with initial energy 340MeV, spanned approximately five orders of magnitude of ionization-rate density. In summary, the cryogenic ion guide is a promising new tool to support the improvement of low-energy beam production at the IGISOL-4 facility which is expected to be operational in 2012.