Peripheral hill sector design for cyclotron

The present disclosure relates to a magnet pole for an isochronous sector-focused cyclotron having hill and valley sectors alternatively distributed around a central axis, Z, each hill sector having an upper surface bounded by four edges: an upper peripheral edge, an upper central edge, a first and a second upper lateral edges. The upper peripheral edge of a hill sector may be an arc of circle whose center is offset with respect to the central axis, and whose radius, Rh, is not more than 85% of a distance, Lh, from the central axis to a midpoint of the upper peripheral edge. Furthermore, the midpoint may be equidistant to the first and second upper distal ends.