Beam Cooling with ionisation losses

This novel type of particle “cooling”, called Ionization Cooling, is applicable to slow ( ) ions stored in a small ring. The many traversals through a thin foil enhance the nuclear reaction probability, in a steady configuration in which ionisation losses are recovered at each turn by a RF-cavity. For a uniform target “foil”, typically few hundred v ≈ 0.1c μg cm thick, transverse betatron oscillations are “cooled”, while the longitudinal momentum spread diverges exponentially since — in the case of dE dx — faster (slower) particles ionise less (more) than the average. In order to “cool” also longitudinally, a chromaticity has to be introduced with a wedge shaped “foil”, such as to instead increase (decrease) the ionisation losses for faster (slower) particles. Multiple scattering and straggling are then “cooled” in all three dimensions, with a method similar to the one of synchrotron cooling, but valid for low energy ions. Particles then stably circulate in the beam indefinitely, until they undergo for instance nuclear processes in the thin target foil. This new method is under consideration for the nuclear production of a few MeV/A ion beams. Simple reactions — for instance Li + D → Li + p — are more favourably produced in the “mirror” kinematical frame, namely with a heavier ion colliding against a gas-jet D2 target. Kinematics is generally very favourable, with angles in a narrow angular cone (around ≈ 10 degrees for the mentioned reaction) and a relatively concentrated outgoing energy spectrum which allows an efficient collection as a neutral gas in a tiny volume with a technology at high temperatures perfected at ISOLDE. It is however of a much more general applicability. The method appears capable of producing a “table top” storage ring with an accumulation rate in excess of 1014 Li-8 radioactive ion/s.