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Theory and Applications of Superconductivity
Academic Editor: Boris Ya. Shapiro
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Updated time: 13 May 2021
Submitted by: Hongye Zhang
Definition: Alternating current (AC) loss is generated due to the movement of magnetic vortices within the superconductor when experiencing time-varying currents or magnetic fields (or both). AC loss can be categorized into transport current loss and magnetization loss based on the AC source. Particularly, when a superconductor carries a direct current (DC) and is simultaneously exposed to an AC field, dynamic resistance occurs and leads to dynamic loss. Quantification and minimization of AC loss are crucial because the produced heat can not only present severe challenges to the cryogenic systems but also impair the reliability of superconducting devices, leaving a safety hazard. To quantify the AC loss of superconductors, analytical formulae, numerical models, and experimental measurements have been widely adopted. Concerning AC loss minimization techniques, the modification of superconductor structures (filamentation and twisting), flux diverters, as well as winding techniques have been widely exploited. This entry serves to clarify the characteristics and quantification methods of AC loss as well as its minimization techniques in superconductors. It is believed to help deepen the understanding of AC loss and deliver a helpful guideline for future research efforts.