D C HOMOPOLAR MACHINES WITH SUPERCONDUCTING FIELD COILS

Rotor 13 carries conductors 14 connected between sets of slip rings 19 and 20 which co-operate with brush sets 21 and 22. Fixed superconducting field coils 15 and 16 are each split into axially-spaced sections 15A, B and C and 16A, B and C to increase the uniformity of the field at the surface of the slip rings and minimize the field component perpendicular to that surface. The number, length and spacing of the field coil sections is chosen to give the required field. Rings of ferromagnetic material may be disposed to further modify the field. At the outer ends of the slip ring sets the slip ring surfaces may be inclined to follow the field lines more closely.