Effect of Winding Tension, Support Material, and Epoxy Impregnation on the Strain and Critical Current of YBCO Coil

The critical current (
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_c
) of epoxy impregnated YBCO coil is prone to degrade due to the cumulative radial tensile stress. Winding tension has the advantage to reduce the amount of epoxy resin and decrease the radial tensile stress during cool down process. In this paper, the dry and wet coils wound on copper and polytetrafluoroethylene (PTFE, Teflon) bobbin materials with various winding tensions were manufactured and tested. With increasing the winding tension, the winding strain increased but the thermal strain reduced. The low coefficient of thermal expansion for bobbin and epoxy impregnation could decrease thermal contraction of the innermost layer of coil. The winding tension effectively reduced the degradation of epoxy impregnated YBCO coil. The bobbin materials and winding tension of 10–50 N had no effect on the degradation of
I
_c
. A proper winding tension of 20 N was successfully used to fabricate an epoxy impregnated YBCO coil of 30 turns without degradation