Trapping ions from a fast beam in a radio-frequency ion trap: Exploring the energy exchange with the longitudinal radio-frequency field

Abstract

The possibility of injecting ions from an initially fast moving beam into a multipole radio-frequency (RF) ion trap without the use of buffer gas is described. The chosen trap geometry gives rise to an oscillating electric field along the direction of the incoming ions, and through an analytical model as well as numerical simulations it is demonstrated that the energy exchange between the injected ions and this oscillating field governs the trapping dynamics. Most notably, if ions arrive at the trap during specific phases of the RF field, they can be effectively decelerated and stored with low kinetic energy even if their kinetic energy initially exceeds the depth of the trapping potential well. An experimental apparatus for trapping ions from a fast beam is described, and experimental investigations demonstrating the described trapping dynamics are presented.