Recent development and mass production of high Je 2G-HTS tapes by using thin hastelloy substrate at Shanghai Superconductor Technology

Abstract

Over the past few years, emerging applications such as high current conductors for magnets in compact fusion systems and ultra-high field insert magnets require higher engineering current density (Je) of the second generation high temperature superconductor (2G-HTS) tapes. In this paper, the state-of-art of 2G-HTS tapes with 30 μm Hastelloy substrate at Shanghai Superconductor Technology (SST) are presented. RE1Ba2Cu3O7 (REBCO, RE = rare earth) films with strong artificial pinning centers (APCs) are deposited on 30 μm thick Hastelloy substrate. Compared to those with 50 μm thick substrate, higher average critical current (Ic), better Ic homogeneity and better Ic linearity with film thickness increase are also achieved at 77 K self-field for tapes with 30 μm substrate, where piece lengths are up to 1 km. For a 4 mm wide tape with a total thickness of 35 μm, Ic and non-copper Je values reach 600 A and 450 kA cm−2 at 4.2 K, 10 T (B//c), respectively. Transmission electron microscopy observation reveals formation of mixed landscape defects mainly including high density of splayed nanoroads and stacking faults in the REBCO film thickness direction, which is attributed to the extremely high REBCO growth rate of over 50 nm s−1. The pinning force density (Fp) at 4.2 K, 12 T (B//c) reaches over 800 GN m−3, and the lift factors (defined as the ratio of Ic at 4.2 K, 10 T to Ic at 77 K, self-field) of tapes with large Ic range (100 to 500 A cm−1-w at 77 K, self-field) also show good consistency. The annual production of 10 mm wide tapes with such pinning centers can exceed 200 km for a single set of facility at SST. No significant Ic reduction is observed at bending diameter of 3 mm and the proof strength (Rp0.2_0) is 812 MPa, both measured at liquid nitrogen temperature.