Sympathetic cooling and reactions in an ion-neutral hybrid trap.*

We investigated the sympathetic cooling of $Na^{+}$ ions by collisions with cold Na atoms in a hybrid trap consisting of a MOT and a linear Paul trap. Since $Na^{+}$ is a closed shell ion and lacks optically accessible transitions from the ground state, we applied four general non-optical techniques for thermometry in a hybrid trap. Simulations using SIMION 7.0 and also our experimental results suggest that there is a cooling effect, but this effect is modest for large numbers of ions $(\sim 10^{4})$. When we attempted to use the Na MOT to cool $Ca^{+}$ ions, there was evidence of a surprisingly large charge exchange rate, to be discussed.