A permanent magnet rotor arrangement comprising: a rotor drum having a radially outer surface; a circumferential array of magnet carriers (8; 104) secured to the rotor drum for rotation therewith, each magnet carrier (8; 104) having a radially outer surface and a laminated construction; and at least one pole piece (10; 106) made of permanent magnet material located on the radially outer surface of each magnet carrier (8; 104); wherein the magnet carriers (8; 104) are mounted in abutment with each other in the circumferential direction to form a continuous, annular, magnet carrier assembly; wherein each magnet carrier (8; 104) extends axially along the rotor drum; wherein each magnet carrier (8; 104) is releasably affixed to the rotor drum by at least one non-magnetic fixing member (16; 112); wherein each magnet carrier (8; 104) is supported at both of its circumferential edges by one of: at least one non-magnetic support member, at least one magnetic support member integrally formed with the magnet carrier and wherein a non-magnetic spacer is positioned between each support member and the rotor drum to prevent magnetic flux from entering the rotor drum, and at least one magnetic support member integrally formed with the rotor drum and wherein a non-magnetic spacer is positioned between each support member and the magnet carrier to prevent magnetic flux from entering the rotor drum; wherein the non-magnetic fixing members (16; 112) and the support members (18; 114) space the magnet carriers (8; 104) apart from the radially outer surface of the rotor drum in the radial direction to define a space or void therebetween. a rotor drum having a radially outer surface; a circumferential array of magnet carriers (8; 104) secured to the rotor drum for rotation therewith, each magnet carrier (8; 104) having a radially outer surface and a laminated construction; and at least one pole piece (10; 106) made of permanent magnet material located on the radially outer surface of each magnet carrier (8; 104); wherein the magnet carriers (8; 104) are mounted in abutment with each other in the circumferential direction to form a continuous, annular, magnet carrier assembly; wherein each magnet carrier (8; 104) extends axially along the rotor drum; wherein each magnet carrier (8; 104) is releasably affixed to the rotor drum by at least one non-magnetic fixing member (16; 112); wherein each magnet carrier (8; 104) is supported at both of its circumferential edges by one of: at least one non-magnetic support member, at least one magnetic support member integrally formed with the magnet carrier and wherein a non-magnetic spacer is positioned between each support member and the rotor drum to prevent magnetic flux from entering the rotor drum, and at least one magnetic support member integrally formed with the rotor drum and wherein a non-magnetic spacer is positioned between each support member and the magnet carrier to prevent magnetic flux from entering the rotor drum; at least one non-magnetic support member, at least one magnetic support member integrally formed with the magnet carrier and wherein a non-magnetic spacer is positioned between each support member and the rotor drum to prevent magnetic flux from entering the rotor drum, and at least one magnetic support member integrally formed with the rotor drum and wherein a non-magnetic spacer is positioned between each support member and the magnet carrier to prevent magnetic flux from entering the rotor drum; wherein the non-magnetic fixing members (16; 112) and the support members (18; 114) space the magnet carriers (8; 104) apart from the radially outer surface of the rotor drum in the radial direction to define a space or void therebetween.