An ion guide for guiding an ion beam along an ion path, said ion guide having a centerline corresponding to said ion path, and a plurality of electrodes extending along said centerline, wherein said electrodes are formed by conductive electrode plates which are radially arranged around said centerline , wherein each of said electrode plates has a radially inner edge that is closest to the centerline , and wherein an inner envelope of the radially inner edges defines an ion guide volume, wherein said electrode plates are connected or connectable with an RF voltage source for applying voltages collectively confining ions within said ion guide volume, and wherein the electrode plates have a wedge-like profile with a thickness increasing in a radially outward direction characterized in that the radially inner edges of the electrode plates are, at least in a section along the length of the ion guide , conically converging or diverging from the centerline , wherein the average angle between the radially inner edges of the electrode plates and the centerline within said section is less than 45° and is 0.1° or more, and in that the ratio of the thickness of each electrode plate close to its radially inner edge and the inter-plate distance, at any given position along the centerline , is between 0.5 and 6.0, wherein the inter-plate distance is defined as the distance between the radially inner edges of adjacent electrode plates at a given position along said centerline , wherein in case the radially inner edge of the electrode plates is not rounded, said thickness close to the radially inner edge corresponds to the thickness at the radially inner edge, and in case the radially inner edge is rounded, the thickness is to be determined sufficiently away from the apex to be outside the rounded portion, wherein at any given circle around and along the centerline, the ratio between the width of the wedge-like electrode plate in circumferential direction and the width of the adjacent gap is identical, or deviates from the average ratio by less than 20% . said electrodes are formed by conductive electrode plates which are radially arranged around said centerline , wherein each of said electrode plates has a radially inner edge that is closest to the centerline , and wherein an inner envelope of the radially inner edges defines an ion guide volume, wherein said electrode plates are connected or connectable with an RF voltage source for applying voltages collectively confining ions within said ion guide volume, and wherein the electrode plates have a wedge-like profile with a thickness increasing in a radially outward direction characterized in that the radially inner edges of the electrode plates are, at least in a section along the length of the ion guide , conically converging or diverging from the centerline , wherein the average angle between the radially inner edges of the electrode plates and the centerline within said section is less than 45° and is 0.1° or more, and in that the ratio of the thickness of each electrode plate close to its radially inner edge and the inter-plate distance, at any given position along the centerline , is between 0.5 and 6.0, wherein the inter-plate distance is defined as the distance between the radially inner edges of adjacent electrode plates at a given position along said centerline , wherein in case the radially inner edge of the electrode plates is not rounded, said thickness close to the radially inner edge corresponds to the thickness at the radially inner edge, and in case the radially inner edge is rounded, the thickness is to be determined sufficiently away from the apex to be outside the rounded portion, wherein at any given circle around and along the centerline, the ratio between the width of the wedge-like electrode plate in circumferential direction and the width of the adjacent gap is identical, or deviates from the average ratio by less than 20% . <EOS>