Fabrication and Electromagnetic Characterization of Ultrasmall Diameter REBCO Wires

Using ultrathin RE-Ba-Cu-O (REBCO, RE = rare earth) superconductor tapes, we have fabricated of a multilayer round wire with an outer diameter of 1.6 mm on a flexible copper former of 0.8 mm diameter with a critical current of 283 A at 77 K, self-field. A single-layer round wire's angular dependence of critical current in a magnetic field shows near isotropic characteristics. The critical current of a single-layer round wire has been measured over a temperature range of 30-77 K in magnetic fields up to 9 T.

I. Introduction

Superconducting magnets are irreplaceable in particle accelerators [1], nuclear fusion devices [2] and other high-field applications. Nb-Ti and Nb ₃Sn wires have been exclusively used in these applications. Recently significant progress has been made in doped RE-Ba-Cu-O (REBCO, RE = rare earth) superconductor tapes with superior in-field critical current performance at 4.2 K [3]–[5]. Engineering current densities () as high as have been achieved at 4.2 K, 21 T which is more than six times higher than that of Nb₃Sn. Additionally, the superior mechanical property and high critical temperature of REBCO tapes make them a competitive candidate for high-field magnets which operate above 20 T or at a temperature higher than liquid helium. Commercially-available REBCO tapes are flat shaped, with a critical current of a few hundred amperes at 77 K in self-field. One way to use REBCO tape in high-field magnet is to wind the tape directly into a magnet with a large number of turns. This will result in a high inductance, making the quench protection and fast charging of the magnet very hard. This method also places a high demand on the uniformity of the tape.