“White-light” Laser Cooling of a Fast Stored Ion Beam

We report the experimental demonstration of ``white-light'' cooling of a high-velocity ⁷Li⁺ ion beam stored at 6.4% of the speed of light in a storage ring. In a direct comparison with single-mode laser cooling, we show that white-light cooling is much more efficient to counteract strong intrabeam heating and leads to lower longitudinal beam temperatures at higher ion densities, i.e., much higher densities in longitudinal phase space.