Generating Ultralow-Emittance Ion Beams in a Storage Ring

Abstract

Laser cooling of heavy-ion beams in a storage ring is systematically studied with a multiparticle simulation code where not only exact lattice characteristics and space-charge forces but also realistic laser-ion interactions can be incorporated. The resonant coupling method is applied in order to extend the powerful longitudinal photon pressure to the transverse degrees of freedom. It is shown that, in spite of a space-charge-induced tune shift, the synchrobetatron resonance mechanism required for fast damping of transverse oscillations operates throughout the cooling process. Extremely efficient three-dimensional cooling of stored ion beams is thus feasible. It is demonstrated that, at low line density, normalized root-mean-squared emittances of the order of 10(-12) m.rad can be reached in all three directions by employing only existing technologies.

Resonance coupling induced enhancement of indirect transverse cooling in a laser-cooled ion beam

“…Too low a transverse cooling rate simply makes it impossible to overcome various heating sources including Coulomb collisions (IBS), space-charge-induced collective resonances, lattice-imperfection-induced resonances, and the vertical instability pointed out by Madsen et al In the MD study cited above [29], the total number of 24 Mg þ ions in S-LSR is only about a thousand, 4 orders of magnitude smaller than the present experiment. With 10 7 ions in the ring, Coulomb collisions strongly affect the attainable beam temperature as demonstrated in Fig.…”

“…MD simulations by Yuri and Okamoto, assuming the S-LSR lattice [28,29], suggest that it is possible to generate (1), which means that the horizontal beam temperature is reduced to $200 K by indirect laser cooling. 1 In this regard, the S-LSR lattice has a relatively good beamdynamic feature compared to the lattices of other cooler storage rings.…”

Crystalline beams in dispersion-free storage rings

“…Consequently, even a 1D string crystal oscillates periodically on the horizontal plane. 3D shell crystals also execute horizontal head-tail oscillations that have the same periodic pattern as in the case of 1D strings [21,28]. This strongly suggests that rf cavities should be placed symmetrically in every lattice period to stabilize a large bunched crystalline beam.…”

“…As pointed out in previous papers [16,21,28], the dynamic behavior of a bunched Coulomb crystal is much more complicated than that in a Paul ion trap. Since individual particles either gain or lose energy at rf cavities, the transverse motion is seriously affected by the energy modulation through the dispersive coupling, in other words, the cross term xp z in the Hamiltonian.…”

“…III. The MD code CRYSTAL [21] is employed in Sec. IV to show that multidimensional crystalline beams can be generated in dispersion-free rings without tapering the cooling force.…”