Ordered ion structures in a quadrupole storage ring

Laser-induced cooling nowadays allows to cool stored ions down to temperatures in the millikelvin range, or even below that. Thus novel experiments can be performed with ordered, strongly coupled ion structures. The article reports on experiments with a quadrupole storage ring 115 cm across, in which ordered structures of laser-cooled Mg+ ions have been produced. In the course of the experiment, the first structure observed is a linear ion chain, which with increasing ion density develops into a zic-zac structure and eventually into helical structures. Further increased ion densities lead to multiple, concentric shell structures. All these structures observed are similar to those expected to be produced through cooling in high-energy storage rings. (orig.)