Transverse Laser Cooling of a Fast Stored Ion Beam through Dispersive Coupling

Transverse laser cooling of a fast stored ⁹Be⁺ ion beam based on a single-particle force independent of the ion density is demonstrated at the Heidelberg Test Storage Ring. The cooling scheme exploits longitudinal-horizontal coupling through ring dispersion and the transverse intensity profile of the longitudinally merged laser beam. By linear betatron coupling the horizontal force is extended to the vertical degree of freedom resulting in true 3D laser cooling. The observed transverse-cooling mechanism represents an important step towards crystalline ion beams.