Influence of a geometrical perturbation on the ion dynamics in a 3D Paul trap

In ion traps, the purity of the Quadrupole potential is essential. Any perturbations in potential caused by geometrical imperfections or the presence of other ions alter the dynamics of trapped ions. In this paper the effect of a particular perturbation on dynamics of trapped ions in a 3-D quadrupole trap is analyzed and we have compared the experimental findings with simulations. To see the effect of geometrical perturbation, the position of a filament reaching into the trap (which acts as the perturbing element) is altered. The equi-frequency line on the a−qa−q Mathieu plot was scanned at different filament insertion heights. We studied the effect of filament current and the duration of loading. The distorted potential within this trap has been theoretically calculated and simulated using SIMION. An analytical expression for potential inside the trap is fitted to the potential values obtained from the simulation and the numerical solutions of the equation of motion of trapped ions is obtained. The 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.