Rapid assessment of REBCO CC angular critical current density J <sub>c</sub>(B, T = 4.2 K, θ) using torque magnetometry up to at least 30 tesla
J. Jaroszyński, A-M Constantinescu, George E. Miller, Aixia Xu, Ashleigh Francis, T. P. Murphy, D. C. Larbalestier
Abstract
Abstract Detailed design of REBa 2 Cu 3 O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi/> <mml:mrow> <mml:mn>7</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:math> (REBCO)-based magnets ideally relies on knowledge of the full angular and wide temperature range characterization of the critical current <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:math> of the REBCO coated conductors (CC) at high magnetic fields. In practice, however, obtaining <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>B</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>,</mml:mo> <mml:mi>θ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> data by the commonly used electrical transport technique is expensive, tedious, and difficult, due to high critical current values that exceed 2000 A for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>|</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>|</mml:mo> </mml:mrow> <mml:mi>a</mml:mi> <mml:mi>b</mml:mi> </mml:math> -plane ( θ = 90 deg). The conductors are often damaged during angular transport measurements at angles approaching the ab -plane. Therefore, so far, REBCO magnets have been designed without full <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>B</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>,</mml:mo> <mml:mi>θ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> data sets. Here, we present <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>J</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mi>B</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>,</mml:mo> <mml:mi>θ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:math> results for more than twenty samples of CC all made to the same advanced pinning specification produced by SuperPower Inc. For this, we employed torque magnetometry, benchmarking the results to transport <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> </mml:msub> </mml:math> measurements mostly made away from ab -plane, finding good agreement with scaling factors ≈1–1.3. What is striking is the huge variety of properties exhibited by the samples, even for CC made recently. Given the huge attention now being paid to the effects of screening currents and to the torques generated by offsets between the tape plane and the local magnetic field vector, our data set suggests some caution in detailed design of such magnets without having data of the type presented here.