Ultra-Small Diameter Round REBCO Wire With Robust Mechanical Properties

The compressive bend diameter (REBa
₂
Cu
₃
O
_x
(REBCO) layer facing inward in all cases) dependence of critical current (Ic) of commercial (stabilizer free, 50-μm substrate) and thin (22-μm substrate) REBCO tapes has been compared after copper electroplating only on REBCO side and on both sides of the tape. We have experimented with different substrate and stabilizer thickness of the REBCO tape to maximize high I
_c
retention while the tape is bent into smaller diameter forms. Single-layer round wires made by winding the most robust REBCO tapes on 0.81-mm copper former have been tested for its critical current at different twist pitches under combined torsion and compressive strains. Using the best tape, the critical current of a multilayer round wire of 1.6-mm overall diameter (0.81-mm core) has been tested under bending over a range of diameters from 12 to 3 cm. These studies confirm the superior retention of critical current under combined effect of high torsion and compressive bend strain of our ultra-small diameter REBCO wires.