Recent results from laser cooling experiments in ASTRID – real-time imaging of ion beams

We describe the latest results from laser cooling experiments using Mg ions in the ASTRID storage ring. In particular, we focus on the transverse dynamics of the longitudinally cooled beam. We have developed a direct imaging technique, using the laser fluorescence to determine the horizontal and vertical distributions in the beam. The beam can now be imaged in real time, using an image intensifier and a fast-sampling CCD camera. The sensitivity and resolution of this system allow direct observation of beams which are well below the longitudinal charge density corresponding to a “string” of particles. We have observed space-charge limitations to the transverse beam sizes, as well as intriguing instabilities of very low-current beams.