A permanent magnet excited synchronous machine comprising: - a stator, said stator having a plurality of circumferential stator teeth; - a rotor configured to rotate in said stator; - a rotary shaft supporting said rotor for rotation on its axis; - a salient pole on said rotor, said salient pole including a shank, said salient pole including a shoe on said shank; - a rectangular cross-section cavity in said salient pole, said rectangular cavity having a cross-section major axis coincident with a chord of a circle delimited by the rotor diameter, said rectangular cavity having a radially-outer top wall parallel to said chord and said major axis; - an exciter permanent magnet in said rectangular cavity; - a plurality of selective flux barrier slots in said salient pole, said plurality of slots disposed radially outwardly of said permanent magnet and between said radially-outer top wall of said rectangular cavity and an external surface of said shoe; characterised in that: - said plurality of slots are disposed in a fan arrangement relative to said chord so that slots of said plurality that are located circumferentially nearer to a main axis of said pole are inclined at a lesser absolute value of inclination angle relative to the main pole axis than are others of said slots relatively located circumferentially farther from the main pole axis; and, - said plurality of slots is a number selected to correspond to the number of said stator teeth radially opposite to said shoe. - a stator, said stator having a plurality of circumferential stator teeth; - a rotor configured to rotate in said stator; - a rotary shaft supporting said rotor for rotation on its axis; - a salient pole on said rotor, said salient pole including a shank, said salient pole including a shoe on said shank; - a rectangular cross-section cavity in said salient pole, said rectangular cavity having a cross-section major axis coincident with a chord of a circle delimited by the rotor diameter, said rectangular cavity having a radially-outer top wall parallel to said chord and said major axis; - an exciter permanent magnet in said rectangular cavity; - a plurality of selective flux barrier slots in said salient pole, said plurality of slots disposed radially outwardly of said permanent magnet and between said radially-outer top wall of said rectangular cavity and an external surface of said shoe; characterised in that: - said plurality of slots are disposed in a fan arrangement relative to said chord so that slots of said plurality that are located circumferentially nearer to a main axis of said pole are inclined at a lesser absolute value of inclination angle relative to the main pole axis than are others of said slots relatively located circumferentially farther from the main pole axis; and, - said plurality of slots is a number selected to correspond to the number of said stator teeth radially opposite to said shoe. - said plurality of slots are disposed in a fan arrangement relative to said chord so that slots of said plurality that are located circumferentially nearer to a main axis of said pole are inclined at a lesser absolute value of inclination angle relative to the main pole axis than are others of said slots relatively located circumferentially farther from the main pole axis; and, - said plurality of slots is a number selected to correspond to the number of said stator teeth radially opposite to said shoe.