Patent ID: 7554240

Claim:
A tubular electrical machine comprising: a radially outer member having a substantially cylindrical inner surface; a radially inner member that is coaxially disposed within the outer member such that the inner member is reciprocally movable relative to the outer member in an axial direction; a plurality of axially spaced armature coils that are electrically insulated from one another and are formed as part of one of the outer member and the inner member; and a plurality of axially spaced superconducting coils that are formed as part of the other one of the outer member and the inner member, each super conducting coil, during operation of the tubular electrical machine, being maintained in a superconducting state, and an electrical current being supplied to each superconducting coil in such a manner that a current flowing around each superconducting coil is in an opposite direction to a current flowing around the axially adjacent superconducting coil or coils.