Figure 10: (a) Photograph of two double-sided YBCO wafers on 7 1 × 7 5  mm² 𝑟 -plane sapphire substrates with CeO2 buffer layers. Obvious is the mirror-like, homogeneous appearance of the YBCO films. (b) Mapping of the critical current density (77 K) of such a 7 1 × 7 5  mm² YBCO wafer with two YBCO films at both wafer sides, demonstrating the very good homogeneity of 𝑗 c using the “ 𝑗 c -scan Leipzig.” As much as 15 consecutively deposited 7 1 × 7 5  mm² YBCO wafers showed such excellent 𝑗 c -homogeneity, indicating a high reproducibility of the “space qualified” large-area PLD process [911].