Ion guide with varying multipoles

An ion guide, comprising:

• an ion entrance end;
• an ion exit end;
• and
• a plurality of electrodes,
• wherein at least one electrode of the plurality of electrodes is elongated along an ion guide axis from the ion entrance end to the ion exit end,
• wherein the at least one electrode of the plurality of electrodes includes a cross-section that includes a quadrilateral shape,
• wherein a size of the cross-section increases at a constant taper along the ion guide axis from the ion extrance end to the ion exit end,
• wherein the plurality of electrodes are spaced from each other around the ion guide axis to surround an ion guide interior,
• wherein the plurality of electrodes include inside surfaces that are disposed at a variable radius from the ion guide axis, and
• wherein the inside surfaces inscribe a variable circle on the ion guide axis.