Observation of instabilities in a Paul trap with higher-order anharmonicities

Systematic measurements of the relative ion number stored in a Paul trap within the stability diagram given by the solution of the equation of motion reveal many lines, where only few or no ions can be confined. The observations can be explained by the presence of perturbations from higher-order components in the trapping potential, which is a quadrupole potential in the ideal case. The resonances follow the equation (n_r/2)_r + (n_r/2)_z = 1,n_r +n_z =N, where 2N is the order of the perturbation,n_r,n_z are integer and_r,_z are stability parameters of the trap. The experiments were performed on H⁺ and H₂⁺ ions, which are detected after a storage time of 0.3 s by ejection from the trap.