US Patent 9000364 Electrostatic ion trap

An electrostatic ion trap confines ions of different mass to charge ratios and kinetic energies within an anharmonic potential well. The ion trap is also provided with a small amplitude AC drive that excites confined ions. The mass dependent amplitudes of oscillation of the confined ions are increased as their energies increase, due to an autoresonance between the AC drive frequency and the natural oscillation frequencies of the ions, until the oscillation amplitudes of the ions exceed the physical dimensions of the trap, or the ions fragment or undergo any other physical or chemical transformation.