Beam cooling with ionization losses

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 568; no. 2; pp. 475 - 487
• Main Authors: Rubbia, C., Ferrari, A., Kadi, Y., Vlachoudis, V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2006
• Subjects: Beta beams; Ionization cooling; Radioactive ion beams; 29.20.−c; Ionization cooling; 41.75.Ak; 41.75.Lx; 12.15.Ff; Beta beams; 29.25.Rm; Radioactive ion beams
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2006.02.161

This novel type of Ionization Cooling is an effective method in order to enhance the (strong) interaction probability of slow (few MeV/A) ions stored in a small ring. The many traversals through a thin target strongly improve the nuclear reaction rate with respect to a single-pass collision, in a steady configuration in which ionization losses of a target “foil” (typically few hundred μg/cm 2 thick) are continuously recovered by an RF-cavity. With a flat foil, betatron oscillations are “cooled”, but the momentum spread diverges exponentially, since faster (slower) particles ionize less (more) than the average. In order to “cool” the beam also longitudinally, a chromaticity has to be introduced with a wedge-shaped “foil”. Therefore, in equilibrium conditions, multiple scattering and straggling are both balanced by phase-space compression. Classic Ionization Cooling [A.A. Kolomensky, Atomnaya Energiya 19 (1965) 534; Yu.M. Ado, V.I. Balbekov, Atomnaya Energiya 31(1) (1971) 40–44; A.N. Skrinsky, V.V. Parkhomchuk, Sov. J. Nucl. Phys. 12 (1981) 3; E.A. Perevendentsev, A.N. Skrinsky, in: Proceedings of the 12th International Conference on High Energy Acceleration, 1983, p. 485] is designed to cool the direct beam until it has been compressed and extracted for further use. In practice, this limits its applicability to non-interacting muon beams. Instead, in this new method, applicable to strongly interacting collisions, the circulating beam is not extracted. Ionization cooling provides “in situ” storage of the beam until it is converted by a nuclear interaction with the target. Simple reactions—for instance 7 Li + D → 8 Li + p —are more favourably produced in the “mirror” kinematical frame, namely with a heavier ion colliding against a gas-jet D 2 target. Kinematics is generally very favourable, with angles in a narrow angular cone (around ∼10° for the mentioned reaction) and with a relatively concentrated outgoing energy spectrum which allows an efficient collection of 8Li as a neutral gas in a tiny volume, a technology perfected by ISOLDE at high temperatures. The method should be capable of producing a “table top” storage ring with an accumulation rate in excess of 10 14 8Li radioactive ion/s. It has however a much more general applicability to many other nuclear reactions.