Octupolar excitation of ion motion in a Penning trap—A study performed at LEBIT

The excitation of the motion of ions in a Penning trap at twice their cyclotron frequency, 2νcνc, by means of an azimuthal octupolar rf field has been studied. Presented is the first experimental verification of such an rf octupolar excitation. Compared to ion excitation at νcνc by means of quadrupolar fields an increased resolving power is observed in the cyclotron resonance curves, which may have important implications for Penning trap mass measurements. Numerical simulations have been used to characterize important properties of this type of excitation in detail and to predict the behavior of the ion motion under realistic conditions. Good agreement with the experimental observations is observed. Furthermore, the quadrupolar excitation of the ion motion at νcνc has been revisited and its dependence on the phase of the ion motion and the rf field been studied.