Finite Element Analysis of AC Losses in Pancake Coils Wound Using Two-Ply Bundle Conductor

AC losses in stacked bundle conductors exposed to external magnetic fields are numerically evaluated using a two-dimensional finite element method formulated with a self-magnetic field owing to currents induced in an analysis region. The bundle conductor is composed of two pieces of (Re)BCO coated conductors without electrical insulation to improve the thermal stability. In the analysis models, an idealized copper layer is sandwiched between a pair of superconducting layers in every bundle conductor. The external magnetic fields are increased monotonically from zero to simulate the electromagnetic responses in parts of a single pancake coil for a high field magnet. To understand only the geometrical effect on AC loss, the superconductors are assumed to be subject to the Bean model, in which the critical current density is independent of the local magnetic field. The influences of the number of bundle conductors, gap between bundle conductors, and applied angle of the magnetic field on AC loss are investigated.