EXTERNAL-ION ACCUMULATION IN A PENNING TRAP WITH QUADRUPOLE EXCITATION ASSISTED BUFFER GAS-COOLING

A pulsed ion beam from an external source is injected into a Penning trap and accumulated by repeatedly lowering the electric potential of the entrance end cap. This lowering is performed only partially, i.e. a trapping well is retained during ion capture to prevent the ions already captured from escaping. For the same reason the newly captured ions have to be cooled, which is achieved by buffer gas collisions. To prevent radial ion loss, the ions are exposed to azimuthal quadrupole excitation. By choosing the appropriate frequency (range) this method (selective quadrupole excitation assisted capture and centering (SQUEACE)) allows a mass selection during the capture process and leads to a centering of those ions in the Penning trap. The multiple ion bunch capture results in a significant improvement in signal-to-noise ratio and a decrease in experiment duration.