During the past 25 years, worldwide R&D efforts were concentrated on development of REBCO coated conductor (C.C.), which was expected to have the strongest pinning properties in wide temperature/field range. The in-field performance for REBCO conductors still have growth potential by using artificial pinning centers (APC), as BMO doping technology with nanometer size rod-like structure, etc. But it was a tough challenge to get end-to-end uniformity even for non-APC REBCO conductors, because c.c. is essentially characterized as reel-to-reel sequential process for single-crystalline-like triaxially textured films on flexible metal substrate, where it is still the only way to avoid intergrain weaklinks for REBCO wires.
In order to obtain good longitudinal Ic homogeneity of c.c., we had chosen hot-wall type pulsed-laser-deposition (PLD), which realized quite homogeneous crystalline growth conditions for REBCO deposition by furnace-like, nearly equilibrium substrate heating, on sharply textured buffer layers formed by using large-area ion-beam- assisted-deposition (IBAD). As a results, reliable production line of homogeneous non-doped REBCO tapes with lengths over 500 m had been developed with typical Ic performances over 500 A/cm at 77 K in the self-field and over 1000 A/cm (Jc=5-6 MA/cm2) at 30 K in 2 T. Recent years we applied the process for introduction of rod-like APC as BaMO3 (BMO, M : Zr or Hf) -doped REBCO conductors and found a productive process condition of BMO-doped high-performance tapes with good longitudinal homogeneity. 300-600m long class uniform BaHfO doped EuBCO tapes were formed with productive high growth rate of 20-30 nm/sec, being faster than commercial non-doped conductors, which had also large Ic of 1700-2000A/cm (Jc=7-8 MA/cm2) at 30K, 2T. The angular dependence of in-field Jc properties were investigated in wide temperature range, and strongly c-axis correlated flux pinning were observed over 30K, especially in those films with the growth rate limited lower than 5 nm/sec, where the minimum values of Jc were not so different from high growth rate over 20 nm/sec. These results indicate reliable controllability of deposition parameters on high-rate APC introduction by using hot-wall PLD process. Ic homogeneity analysis of long-length BMO-REBCO c.c. and the microstructural analysis for the growth of BMO rod-structure would be discussed correlated with growth speed, BMO composition, etc.
This Paper includes the results supported by the New Energy and Industrial Technology Development Organization (NEDO).