Universal, non-monotonic structure in the saturation curves of a linear Paul trap

A common technique to measure ion-atom collision rates in a hybrid trap if the ions have no optical transitions (e.g. alkalis) is to monitor the fluorescence of the neutrals in the presence of a saturated linear Paul trap (LPT). We present numerical simulations, analytical calculations, and experimental results that show that the steady-state ion capacity of an LPT, N_s, exhibits nonlinear, nonmonotonic behavior as a function of ion loading rate, Λ. The steady state as a function of loading rate, N_s(Λ) , shows four distinct regions. In Region I, at the lowest Λ, N_s(Λ) increases monotonically. Then, N_s(Λ) reaches a plateau in Region II, before decreasing to a local minimum in Region III. Finally, in Region IV, N_s(Λ) once again increases monotonically. This behavior appears universal to any Paul trap, regardless of geometry or species trapped. We examine this behavior experimentally as a function of the q stability parameter of the Paul trap and simulate numerically the effect of the particular trap geometry on the onset of each of the four regions.

Funding from NSF Grant PHY-1307874.