An ion trap comprising elongate rods, electrodes, a first circuit, and a second circuit. The rods are for defining the radial extent of a trapping volume. The first circuit is connected to the rods for applying thereto a first RF signal that generates adjacent the trapping volume a radial RF containment field that radially contains ions of different polarities within the trapping volume. The electrodes define the axial extent of the trapping volume. The second circuit is connected to the electrodes for applying thereto a second RF signal that generates adjacent the trapping volume an axial RF containment field that axially contains the ions of different polarities within the trapping volume. The axial RF containment field is independent of the radial RF containment field.