Theoretical expressions for AC losses of superconducting coils in externalmagnetic field and transport current with phase difference

We propose generalized expressions for AC losses in solenoidal coils of sup erconducting wires without twisting, to which both alternating transport cu rrent and AC magnetic field are applied with a phase shift. We assume that the coils can be approximated by a homogeneous superconducting sheet and th at the electromagnetic behavior can be described by the Bean's critical sta te model, in which the magnitude of local current density is equal to the c ritical current density or zero. The results show that the AC losses are pl otted on a master curve independent of the phase shift for the maximum magn etic field applied to the coil, and that the AC loss properties for the max imum field are similar to those of transverse-field losses. (C) 2001 Elsevi er Science B.V. All rights reserved.