Ac Losses in Type-II Superconductors

This paper discusses the physics of ac losses in type-II superconductors and in multifilamentary superconducting-normal composite conductors. As an introduction, the ac eddy-current losses in a homogeneous normal conducting cylindrical specimen subjected to an alternating applied magnetic field are briefly reviewed. The ac losses in a superconducting cylindrical specimen are discussed in detail next, with emphasis on the losses in a specimen subjected to an alternating applied longitudinal magnetic field. In general, dissipation occurs via both flux-flow losses, which are analogous to eddy-current losses in the normal state, and hysteretic losses, which arise from bulk and surface pinning as well as annihilation of vortices of the opposite sense. Tests are suggested by which the dominant loss mechanisms can be identified. Special considerations are noted for the case of the high-temperature superconductors. Finally, the losses in multifilamentary superconducting-normal composite conductors are discussed.

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