Basic approach to AC losses in HTS wires exposed to various types of electromagnetic configuration

AC loss in superconducting materials can be estimated, in general, by consi dering Poynting's vector, electromagnetic power flow, on a closed surface s urrounding the sample in a cyclic electromagnetic environment. On the basis of energy conservation, the total amount of the power now that penetrates into the sample during the period of the electromagnetic environment is equ ivalent to the AC loss. By using this basic concept of the AC loss, errors in AC loss measurement with three types of pickup coil methods are first co nsidered in relation with the geometrical configuration of the sample coil and the pickup coils. It is indicated from the analytical formulation of th e AC loss measured that the error is strongly affected by the arrangement o f the cancel coil and that the most proper arrangement is the coaxial type, where the sample coil is set coaxially and concentrically between the inne r cancel coil and the outer main pickup coil. Secondly, the geometrical err or in a simple method proposed to measure various types of AC loss is also discussed. It is suggested by the analytical consideration that this method has a high accuracy in the AC loss measurement even in comparison with the coaxial type of pickup coil method. Finally, experimental results measured by the simple method for various types of AC loss in Bi-2223 tapes are com pared with numerical simulation with the measured E-J characteristic. (C) 2 000 Elsevier Science B.V. All rights reserved.