An ion guide is disclosed comprising a first array of electrodes and a second array of electrodes and one or more apertures or ion exit regions. The first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions. The ion guide comprises a first device arranged and adapted to apply an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays, and a second device arranged and adapted to apply one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a second (r) direction towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions.