Density limitations in a stored laser-cooled ion beam

We present a new technique for transverse beam profile diagnostics of a stored ion beam, imaging the fluorescence light from a laser-excited ion beam onto a high resolution charge-coupled device detector. This technique has much higher sensitivity and spatial resolution than conventional techniques. Using this method we have obtained evidence for space-charge-dominated behavior of a stored, laser-cooled beam of Mg-24(+) ions. However, the transverse size of the longitudinally cooled beam is larger than that expected for a space-charge limited beam. This seems to confirm expectations from molecular dynamics simulations, showing that to reach a crystalline beam, other techniques have to be applied.