Characteristics of an HTS Pancake Coil in Persistent Current Mode Using Wind-and-Flip Winding Method

It has been well known that a coated conductor (CC), 2G superconducting tape, shows a higher critical current and better performance than the 1G, BSCCO one. However, there has still been no way to make a superconducting joint with CC, so it has been almost impossible to build a CC superconducting magnet in persistent current mode. As a viable solution for this, we have proposed a special winding technology called the Wind-and-Flip method. It shows a new possibility for the generation of a persistent current mode in a magnet with CC. First, we partially cut a wide CC tape into two pieces along the tape except at both end parts like cutting the abdomen of a fish. Then we wind two pancake coils with the cut but connected CC tape. Finally, one of the two coils is turned over, and then the magnetic fields from both coils would have the same direction with each other. In this paper, we made two high-temperature superconducting double pancake windings by the Wind-and-Flip method. One has turn-to-turn insulation layers while the other does not. They both have oxygen-free copper bobbins for the conduction cooling. First, they were magnetized by field cooling within a fine background magnet, and operated in persistent current mode at 77 K. As a result of the experiment, we measured and compared temporal stabilities for both pancake windings to investigate the possible use of these windings for magnetic resonance imaging or nuclear magnetic resonance applications. We have future plans of measuring the temporal stabilities of similar windings under lower temperatures and confirm the possibility of a high-field high-temperature superconducting magnet, which will be fabricated by stacking these pancake coils with larger cold bore size.