Review on AC losses in superconductors

Paper presents principal results obtained during the last years in the research of AC losses in superconductors with regard to the magnet technology. Special emphasis is given on these aspects which are important in demonstrating the technical feasibility and economical advantages of AC superconducting windings. In the domain of hysteresis losses paper reports mainly on the extension of the theory of losses in superconducting cylinder placed in transverse alternating and/or rotating magnetic field of arbitrary amplitude as well as on the problems related to the case when the field is not perpendicular to the cylinder axis and the anisotropy of pinning force is important. The progress in substantial reducing of the filament diameter by improving existing technologies of multifilamentary superconductors as well as by elaborating new ones /in situ/ and its impact on hysteresis losses is presented. Results obtained in the research of eddy current and coupling current losses at high amplitudes and rates of field variation, as well as at presence of DC and/or AC transport current in multifilamentary conductors in transverse alternating and/or rotating fields are discussed. Some problems arising in high current monolithic and/or multistage assembled cables with regard to AC losses are briefly reviewed. Resuming the mentioned theoretical and experimental results and using the practical experience of pulsed superconducting magnets for frequencies of about 1 Hz main lines of a program of developing AC superconducting windings for higher frequencies are outlined. The author is with Electrotechnical Institute of the Electro-Physical Research Center, Slovak Academy of Sciences, Dúbravská cesta, 809 32 Bratislava, Czechoslovakia