On the use of intentionally-designed defect distributions in REBCO superconducting cables and magnets

Abstract This paper challenges the conventional wisdom that mechanical defects are always a negative feature in superconductors and that a superconducting cable’s steady-state electrical behavior is an inherent characteristic that cannot be controlled. Intentionally-designed mechanical defect distributions are demonstrated as a technique for modifying the current distribution of high-temperature superconductor cables using a defect characterization platform that enables numerical prediction and experimental measurement in a five-tape rare-earth barium copper oxide (REBCO) cable ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mtext>c</mml:mtext> </mml:msub> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 438 A at 77.4 K, self-field). A new technique for tuning local critical current in REBCO tapes using intentional mechanically-induced partial defects is developed and validated. A cable containing a model-guided configuration of partial defects is studied, demonstrating numerically and experimentally the use of defects as a tool for controlling current distribution, in this case by forcing significantly improved current uniformity as a function of both operating current and axial position compared with a no-defect cable, which is shown to be accomplished with modest additional defect-induced power dissipation. Intentional defects have several other potential applications in superconducting cables and magnets, such as improvement of defect tolerance, prediction of the power law exponent, efficient dissipation of screening currents, and quench diagnostics.