A method of manufacturing a device for manipulating charged particles using an axial electric field as they travel along a longitudinal axis of the device, said method comprising: selecting an electrical potential profile desired to be established along the longitudinal axis of the device for manipulating the charged particles; arranging at least a first plurality of electrodes along the longitudinal axis of the device, wherein the lengths of the electrodes in the direction along the longitudinal axis of the device vary as a function of the distance along the longitudinal axis of the device; connecting one or more first DC voltage supplies to said first plurality of electrodes, wherein the one or more DC voltage supplies are configured to apply one or more DC voltages to the first plurality of electrodes in use; arranging a second plurality of electrodes along the longitudinal axis of the device, wherein one of the second plurality of electrodes is arranged between each longitudinally adjacent pair of electrodes in the first plurality of electrodes; connecting one or more second DC voltage supplies to said second plurality of electrodes, wherein said one or more second DC voltage supplies are configured to maintain each of the second plurality of electrodes at a DC voltage in use; and selecting said lengths of the electrodes in said first plurality of electrodes, the voltages applied to the first and second plurality of electrodes and the locations of said electrodes along the longitudinal axis of the device so that said electrical potential profile is established along the longitudinal axis of the device in use; characterized in that said one or more first DC voltage supplies and/or said one or more second DC voltage supplies are configured to be pulsed on and off for pulsing the electrical potential profile on and off. selecting an electrical potential profile desired to be established along the longitudinal axis of the device for manipulating the charged particles; arranging at least a first plurality of electrodes along the longitudinal axis of the device, wherein the lengths of the electrodes in the direction along the longitudinal axis of the device vary as a function of the distance along the longitudinal axis of the device; connecting one or more first DC voltage supplies to said first plurality of electrodes, wherein the one or more DC voltage supplies are configured to apply one or more DC voltages to the first plurality of electrodes in use; arranging a second plurality of electrodes along the longitudinal axis of the device, wherein one of the second plurality of electrodes is arranged between each longitudinally adjacent pair of electrodes in the first plurality of electrodes; connecting one or more second DC voltage supplies to said second plurality of electrodes, wherein said one or more second DC voltage supplies are configured to maintain each of the second plurality of electrodes at a DC voltage in use; and selecting said lengths of the electrodes in said first plurality of electrodes, the voltages applied to the first and second plurality of electrodes and the locations of said electrodes along the longitudinal axis of the device so that said electrical potential profile is established along the longitudinal axis of the device in use; characterized in that said one or more first DC voltage supplies and/or said one or more second DC voltage supplies are configured to be pulsed on and off for pulsing the electrical potential profile on and off.