A method for processing ions in a multipole ion trap, comprising: introducing ions into a first multipole rod set positioned in tandem with a second multipole rod set, each rod set having a first end and a second end, the ions being introduced into the first and second rod sets through said first end of said first rod set; generating RF fields within the first and second rod sets (ST, Q1) so as to radially confine the ions, said RF fields within the first and second rod sets interacting in an interaction region between the second end of the first rod set and the first end of the second rod set to produce a fringing field; generating a barrier field at the second end of said second rod set so as to repel at least a portion of said ions away from the second end of the second rod set and toward the first rod set; and energizing said repelled ions within said second rod set so that at least a portion of said energized ions are repulsed by the fringing field back toward the second end of the second rod set, wherein energizing said repelled ions comprises applying an auxiliary excitation signal to said second rod set so as to resonantly excite ions having a selected m/ z, wherein the auxiliary excitation signal comprises an auxiliary AC waveform having a frequency that substantially matches a secular frequency of said ions having said selected m/z, wherein the auxiliary AC waveform generates a dipolar excitation field, wherein, for the ions having a selected m/z, a q value for the first rod set is greater than a q value for the second rod set such that said ions having the selected m/z are repulsed by the fringing field. introducing ions into a first multipole rod set positioned in tandem with a second multipole rod set, each rod set having a first end and a second end, the ions being introduced into the first and second rod sets through said first end of said first rod set; generating RF fields within the first and second rod sets (ST, Q1) so as to radially confine the ions, said RF fields within the first and second rod sets interacting in an interaction region between the second end of the first rod set and the first end of the second rod set to produce a fringing field; generating a barrier field at the second end of said second rod set so as to repel at least a portion of said ions away from the second end of the second rod set and toward the first rod set; and energizing said repelled ions within said second rod set so that at least a portion of said energized ions are repulsed by the fringing field back toward the second end of the second rod set, wherein energizing said repelled ions comprises applying an auxiliary excitation signal to said second rod set so as to resonantly excite ions having a selected m/ z, wherein the auxiliary excitation signal comprises an auxiliary AC waveform having a frequency that substantially matches a secular frequency of said ions having said selected m/z, wherein the auxiliary AC waveform generates a dipolar excitation field, wherein, for the ions having a selected m/z, a q value for the first rod set is greater than a q value for the second rod set such that said ions having the selected m/z are repulsed by the fringing field.