  The effect of geometrical perturbations on ion oscillation frequencies in a
3-D quadrupole trap is analyzed by theoretical simulations and compared with
the experimental results. Theoretically, the distorted potential within this
non-ideal trap caused by the insertion of filament has been simulated. An
analytical expression for the potential is then fitted and numerical solution
of the equations of trapped ion motion is obtained. Motional frequencies are
then calculated from the Fourier transformation of the simulated ion
trajectories at any given trapping potential and compared with our experimental
findings. The shift in the secular frequency with respect to the level of
insertion of the filament within the trap is evaluated.
