A storage ring for neutral molecules

Electrostatic hexapoles are common tools in physical chemistry for performing state-selection and focusing of molecules. A hexapole can be viewed as a 2D-trap for polar molecules in low-field seeking states. Therefore, by bending such a hexapole into a torus a storage ring for neutral molecules can be formed. We here review our experiments on such a prototype storage ring. The ring is loaded by a decelerated ammonia beam. The forward velocity as well as the longitudinal and transverse velocity spread of this beam can be adjusted prior to injection into the ring. Using a phase-space description it is detailed how loading of a molecular packet into the storage ring can be performed optimally. Various techniques are used to investigate the motion of the molecules in the ring. The stored molecules can be observed for up to 50 round trips, at which point the packet fills up the entire ring. A design is presented for a sectional storage ring in which the longitudinal spreading of the packet inside the ring can be controlled.