Measurement of low-energy Na^+ -- Na total collision rate in an ion--neutral hybrid trap

We present measurements of the total elastic and resonant charge-exchange ion-atom collision rate coefficient $k_{\mathrm{i}\mathrm{a}}$ of cold sodium (\ce{Na}) with optically-dark low energy \ce{Na+} ions in a hybrid ion-neutral trap. To determine $k_{\mathrm{i}\mathrm{a}}$, we measured the trap loading and loss from both a \ce{Na} magneto-optical trap (MOT) and a linear radio frequency quadrupole Paul trap. We found the total rate coefficient to be $7.4\pm 1.9\times {10}^{-8}$ cm${}^3$/s for the type I \ce{Na} MOT immersed within an $\approx 140$ K ion cloud and $1.10\pm 0.25\times {10}^{-7}$ cm${}^3$/s for the type II \ce{Na} MOT within an $\approx 1070$ K ion cloud. Our measurements show excellent agreement with previously reported theoretical fully quantal $\mathit{\text{ab}}\mathit{\text{initio}}$ calculations. In the process of determining the total rate coefficient, we demonstrate that a MOT can be used to probe an optically dark ion cloud’s spatial distribution within a hybrid trap.