Fast growth process of long-length YBCO coated conductor with high critical current density

On the basis of previously reported 10 m long YBCO tape with over 100 A/cm performance, we are working toward scaling up the YBCO coating process to 100 m lengths. We are using a high tape speed of 15 m/h for fabrication of long lengths. To understand the mechanism of high growth rates of YBa₂Cu₃O_7-x (YBCO) on buffered metal substrates, the relationship between critical current density and YBCO film thickness has been systematically investigated. When YBCO thickness was below one micrometer, the critical current density (J_c) was over 2 MA/cm². As YBCO thickness was increased, J_c decreased gradually. However, J_c still remained 0.91 MA/cm² at a YBCO thickness of 4.2 μm. Critical current (I_c) was 380 A across 1 cm wide tape at 77 K. To scale up the YBCO coating process, the deposition rate was increased to a growth rate of 70 nm/s, corresponding to a tape speed of 15 m/h. The average phi-scan rocking curve of YBCO films was ∼3° on 11° buffered metal tape. The omega scan rocking curve (FWHM) was just 1.5°. J_c of 2 MA/cm² at 77 K and self-field was achieved at a high deposition rate of 70 nm/s and a tape speed of 15 m/h by optimizing deposition parameters. The high rate process has been transferred to long lengths and results will be discussed in this manuscript.