Apparatus for detecting ions (4a, 4b), comprising: an ion trap having a first electrode, preferably a ring electrode and also having at least one second electrode, preferably a cap electrode (7a, 7b), a storage signal generator for generating an RF storage signal (U RF), which can be coupled into the at least one first electrode (3; 3a, 3b) in order to generate an electric storage field in the ion trap, an excitation device (6a, 6b) for generating an excitation signal (U stim1, U stim2) for exciting ions (4a, 4b) stored in the ion trap, and also a detector for detecting an ion signal (I Ion1, I Ion2), generated by the excited ions (4a, 4b) wherein the storage signal generator comprises an input for receiving at least one control signal, the storage signal generator configured to set a waveform and at least one of an amplitude (A RF) and a frequency (f RF) of the RF storage signal (U RF) in dependence upon the at least one control signal characterized by further comprising: an electron beam generating device for generating an electron beam that can be fed to the ion trap in order to generate ions (4a, 4b), wherein the electron beam generating device is designed for feeding the electron beam into the ion trap in a pulsed manner, where the electron beam generating device is synchronized with the storage signal generator in order to feed the electron beam to the ion trap only during at least one partial interval (ΔT i, ΔT i+1) of the period duration of the RF storage signal (U RF) in which the RF storage signal (U RF) has a constant amplitude, the at least one partial interval having a duration of between 1% and 10% of the period duration of the RF storage signal. an ion trap having a first electrode, preferably a ring electrode and also having at least one second electrode, preferably a cap electrode (7a, 7b), a storage signal generator for generating an RF storage signal (U RF), which can be coupled into the at least one first electrode (3; 3a, 3b) in order to generate an electric storage field in the ion trap, an excitation device (6a, 6b) for generating an excitation signal (U stim1, U stim2) for exciting ions (4a, 4b) stored in the ion trap, and also a detector for detecting an ion signal (I Ion1, I Ion2), generated by the excited ions (4a, 4b) wherein the storage signal generator comprises an input for receiving at least one control signal, the storage signal generator configured to set a waveform and at least one of an amplitude (A RF) and a frequency (f RF) of the RF storage signal (U RF) in dependence upon the at least one control signal characterized by further comprising: an electron beam generating device for generating an electron beam that can be fed to the ion trap in order to generate ions (4a, 4b), wherein the electron beam generating device is designed for feeding the electron beam into the ion trap in a pulsed manner, where the electron beam generating device is synchronized with the storage signal generator in order to feed the electron beam to the ion trap only during at least one partial interval (ΔT i, ΔT i+1) of the period duration of the RF storage signal (U RF) in which the RF storage signal (U RF) has a constant amplitude, the at least one partial interval having a duration of between 1% and 10% of the period duration of the RF storage signal.