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Description
This work presents a graded parallel-wound (GPW) coil technique for high temperature superconductor (HTS) magnet consisting of multiple pancake coils. The coil is wound by parallel-stacked HTS tapes, all the coils are connected in series, so that they have a same transport current. The key idea is to assign number of parallel-stacked tapes to pancake coils on different position of the magnet: the top and bottom pancakes have most parallel-stacked tapes as well as lowest overall current density, and the middle pancakes have least parallel-stacked tapes as well as highest overall current density. The GPW technique minimizes the detrimental anisotropy in current-carrying capacity of HTS tape, and enable all the HTS pancake coils on different position have similar ratio of transport current to critical current. It enables HTS magnets to be highly compact, minimum tape usage as well as magnet price. A 25T@20K HTS magnet is developed to validate the GPW technique. The magnet generates a 25 T field at the center, a record high in magnetic fields for operating temperature upon 20 K. The total tape usage is reduced more than 40% in comparison to its counterpart wound with single tapes. The results demonstrate strong potential of GPW technique for HTS high field magnets.
