Effects on Jc of pinning center morphology for multiple-in-line-damage in coated conductor and bulk, melt-textured HTS

The properties of discontinuous aligned pinning centers (PCs) created by high-energy heavy-ions are compared for bulk melt-textured and coated conductor HTS. Properties of PCs, which increase Jc (pinning potential and entanglement), and negative properties which decrease Jc (e.g., decreased Tc and percolation paths) are evaluated. Mechanisms are proposed to explain the very large increases in Jc resulting from multiple-in-line-damage (MILD) compared to continuous columnar pinning centers (CCPC). In particular, a mechanism which results in fluxoid entanglement, even for parallel (unsplayed) PCs, is discussed. The same mechanism is found to also account for restoration of much of the pinning potential expected to be lost due to the gaps in MILD PCs. It also accounts for the fact that at high fluence, Jc increases as fluence is increased, instead of decreasing as expected. The very low self-field in coated conductor permits separation of the negative and positive effects of PCs. It is found that parameters developed to quantify the negative effects in bulk melt-textured YBCO, by 63 GeV U238 ions, successfully describe damage to 2.1 μm thick coated conductor by 1 GeV Ru44 ions. Coated conductor at 77 K and self-field is generally known to have Jc about 100 times that of melt-textured YBCO. However, at 77 K and applied field of 1 T, when both forms of HTS are processed with comparable numbers of near-optimum MILD PCs, the difference in Jc is reduced to a factor of 1.3–2. Whereas Jc for melt-textured YBCO increased sharply, by a factor of up to 16.8 for high-fluence MILD PCs, Jc in coated conductor increased by a smaller factor of 2.5–3.0. Nevertheless, 2.1 μm thick coated conductor, with near-optimum MILD PCs, exhibits Jc = 543 kA/cm2 at 77 K and applied field of 1.0 T, and Ic = 114 A/cm-width of conductor. This is the highest value we find in the literature. The phenomenology developed indicates that for optimum MILD PCs in coated conductor, Jc ∼ 700 ± 70 kA/cm2 should be achievable at 77 K, 1.0 T.