Study on a Stacked REBCO Coil Composed of Six Single Pancakes With Electrically Conductive Epoxy Resin

A coil without turn-to-turn insulation, called a no-insulation (NI) coil has been developed. The NI winding technique has been reported to be a promising method of quench protection. In order to apply the NI winding technique to a conduction-cooled REBCO coil, we developed a coil using an electrically conductive epoxy resin. The conductive epoxy resin, in which silver powder was mixed, was applied to the edge of the winding. If thermal runaway of the coil is observed, the excessive current could be automatically bypassed through the conductive epoxy resin. In order to confirm the effect of a larger coil with higher stored energy when using the conductive epoxy resin, we fabricated and tested a stacked coil composed of six single pancakes whose inner diameters and outer diameters were 501 mm and 567 mm, respectively. The coil was tested in liquid nitrogen and under conduction cooling conditions. When the operating current was 256 A at 40 K, the stored energy was 29 kJ, and burn-out of the coil could be avoided. These results show that thermal runaway can be avoided in larger coils with higher stored energy by using conductive epoxy resin.