The Performance of a Practical Size Epoxy Impregnated Pancake Coil Wound With a Polyimide Electro-Deposited (PIED) YBCO-Coated Conductor

A practical size epoxy impregnated single pancake coil, 30 mm in inner diameter and 73 mm in outer diameter, was fabricated using a polyimide electro-deposited (PIED) YBCO-coated conductor. The voltage-current characteristics achieved at 77 and 4.2 K reached coil critical currents without any degradation of coil performance. We reported similar results for a miniature test double pancake coil operated at 77 K. Because the thickness of the polyimide coating was as thin as 10-20 μm, the fraction of the YBCO-coated conductor in the coil winding was greater than 70%, and therefore high overall current density of greater than 500 A/mm² was achieved at 4.2 K. The 3-D digital micrograph of the top end surface of the PIED YBCO-coated conductor single pancake coil winding infers that debonding of the epoxy from the polyimide coating reduces cleavage stress on the YBCO-coated conductor and results in no degradation in coil performance. PIED YBCO-coated conductors are reliable, easy to handle, and extensible to longer conductors; they are applicable to dry winding and soft polymer impregnated winding, in addition to epoxy impregnated winding as is widely used in Formvar-coated NbTi conductors used for nuclear magnetic resonance and magnetic resonance imaging, etc.