Measurement of the Low-Energy Rb$^+$–Rb Total Collision Rate in an Ion-Neutral Hybrid Trap

An ion-neutral hybrid trap is built to study low-energy ion-atom collisions. The ion-neutral hybrid trap is combined with two spatially concentric traps: a linear Paul trap for the ionic species and a magneto-optical trap (MOT) for the neutral species. The total ion-atom collision rate coefficient k(ia) between Rb-87 atoms and optically dark Rb-87(+) ions is measured by monitoring the reduction of the steady-state MOT atoms by sequentially introducing various mechanisms, namely photoionization and ion-atom collisions. In contrast to other experiments, a concise experimental procedure is devised to obtain the loss rates of the MOT atoms due to photoionization and ion-atom collisions in one experimental cycle, and then the collision rate k(ia) of cold Rb-87 atoms with Rb-87(+) ions is deduced to 0.94(+/- 0.24) x 10(-13) m(3)/s with T-i = 3770(+/- 100) K measured by the time of flight of the ion signal. The measurements show good agreement with the collision rate derived from the Langevin model.