Collection, cooling and delivery of ISOL beams

The collection of an ISOL beam in a Penning trap using implantation on a surface that is subsequently manipulated so as to become part of an end electrode of a Penning trap and reionization of the implanted material by heat has already been very productive for high-precision nuclear-mass measurements, even though it is limited to elements that are surface ionizable and the collection efficiencies are never better than about 0.1%. More recently, in 1990 a Paul trap system for electric collection of ions was installed at the ISOLDE-3 facility and collection was demonstrated for a 60 kV beam of 132Xe ions. The purpose of this test setup was to determine the relationship between phase space volume of a typical trap and the collection efficiency that could be obtained in direct capture. For the modest trap used, collection efficiencies of up to 0.2% were achieved. A beam of negative bromine ions was collected by simply reversing the polarities of all voltages used. From the experience with this system it appears feasible to build a Paul trap which is about three times as large in linear dimensions as the existing one and which could be driven at up to 10 kV peak at 1 MHz using a modest rf amplifier (300 W). With moderate prebunching of the injected beam at 1 MHz, this system should achieve collection efficiencies approaching 100%. Based on these results, preliminary design work is being carried out on the collection system to be installed at the ISOLDE Booster facility. Suggestion for other uses of a Paul trap collection system for ISOL beams are presented. (orig.)