Fields and losses in high T/sub c/ conductors

The hysteresis losses in simple shapes and wires are reasonably well understood. Transport losses in tapes follow the Norris equation well. However it is not clear how cables should be treated since agreement with both a cylindrical model and an isolated tape model have been reported. Coupling losses depend on whether the tapes are insulated. If the layers are in contact current distributes itself over a few centimetres length to minimise the central field. For currents close to I/sub c/ the resistance must be taken into account. Changes in spacing between layers lead to significant redistribution, and losses due to the field from other phases could be large. A continuous change of pitch allows current to penetrate to the centre without cutting filaments.