Delamination Avoidance in Epoxy Wet-Wound REBCO Coils by Release Agent Coating

Currently, the REBCO coated conductors are playing more important roles in various superconducting applications, such as high-field magnets, compact fusion tokamaks, etc. But the delamination issue of epoxy-impregnated REBCO coils still challenges the reliability of REBCO applications. In this work, a novel delamination avoidance method that coating a release agent layer on the REBCO tape surface was introduced. The release agent layer could decouple the REBCO tapes and cured epoxy resin to prevent delamination and degradation. The delamination strengths
$\sigma _\mathrm{{d}}$
of REBCO tapes at 77 K were measured by anvil testing method. Then the interface bonding strengths
$\sigma _\mathrm{{b}}$
between REBCO tapes and Stycast 2850FT epoxy at room temperature were also measured. Finally in the controlled experiment the epoxy wet-wound REBCO coil wound by the raw REBCO tapes without paraffin layers degraded significantly after cooling, while the one wound by the tapes with paraffin layers preserved well even after ten thermal cycles. The result indicated the effectiveness of this delamination avoidance method.