Properties of recent IBAD–MOCVD coated conductors relevant to their high field, lowtemperature magnet use

Abstract

BaZrO3 (BZO) nanorods are now incorporated into production IBAD–MOCVD coated conductors. Here wecompare several examples of both BZO-free and BZO-containing coated conductors using critical current(Ic) characterizations at 4.2 K over their full angular range up tofields of 31 T. We find that BZO nanorods do not produce anyc-axis distortion of the critical current densityJc(θ) curve at 4.2 K at any field, but also that pinning is nevertheless strongly enhancedcompared to the non-BZO conductors. We also find that the tendency of theab-planeJc(θ) peak to become cusp-like is moderated by BZO and we define a new figureof merit that may be helpful for magnet design—the OADI (off-axis doubleIc), which clearly shows that BZO broadens theab-plane peak andthus raises Jc 5°–30° away from the tape plane, where the most critical approach toIc occurs in many coil designs. We describe some experimental procedures that may make critical currentIc tests of these very high current tapes more tractable at 4.2 K, whereIc exceeds 1000 A even for 4 mm wide tape with only1 µm thickness of superconductor. A positive conclusion is that BZO is very beneficial for theJc characteristics at 4.2 K, just as it is at higher temperatures, where the correlatedc-axis pinning effects of the nanorods are much more obvious.