A Measurement Method of AC Losses in Superconducting Coils Using Poynting's Vector Method

A new measurement method to determine ac losses in superconducting coils has been proposed, and its validity confirmed experimentally. In this method, the ac losses in the coil can be obtained from measured Poynting's vectors around the coil windings. The Poynting's vectors can be obtained by local magnetic fields and electric fields around the coil. Local magnetic fields and electric fields are measured by pick-up coils and potential leads, which are mounted around the sample coil. These pick-up coil and potential lead pairs are arranged on the inner side, outer side, top, and bottom of the coil windings to cover the entire coil windings. This measurement method has the benefit that ac losses in a coil in a superconducting coil system consisting of multiple coils can be measured. Not only ac losses in the coils but also information on local electromagnetic phenomena in the coils can be obtained from profiles of the Poynting's vectors. In this paper, the details of the measuring method are described, and experiments using a coil wound with Bi-2223 multifilamentary tapes were carried out in liquid nitrogen to confirm the validity of the measurement method.