The elliptical Penning trap: Experimental investigations and simulations

The application of an additional azimuthal quadrupolar electrostatic field to a Penning trap leads to a field configuration referred to as an elliptical Penning trap. The resulting changes of the radial ion motions have been investigated experimentally and by use of simulations. The eigenfrequencies, i.e., the magnetron frequency ω˜− and the reduced cyclotron frequency ω˜+, are found to be shifted with respect to those of the standard Penning trap ω−ω−, ω+ω+, respectively. As the shift of the magnetron frequency ω˜− is larger than that of the reduced cyclotron frequency ω˜+ their sum ω˜++ω˜− is also a function of the ellipticity and no longer equal to the cyclotron frequency in the absence of an electric trapping field ωc=qB/mωc=qB/m. The frequency shifts were investigated for argon and fullerene ions. The experimental studies were performed by time-of-flight (ToF) analysis of the ion cyclotron resonance and by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The experimental and simulated values are in agreement with theoretical predictions [M. Kretzschmar, this issue] when the influence of higher multipole terms is taken into account.