Abstract Body

The uniformity of long REBa₂Cu₃O_7-δ (REBCO, where RE is rare earth element) tapes is a pivotal factor for their practical applications. This uniformity along the length or over the width, affected by variations in growth conditions during the deposition process, such as temperature, plume direction, local oxygen pressure and so on. As the demand for REBCO tapes escalates, addressing this issue has become a pressing concern. This work focuses on a REBCO tape produced using a multi-plume, multi-turn pulsed laser deposition system. The microstructure and current carrying capacity of the tape were characterized to understand the causes of uniformity in the transverse direction of the REBCO layer. Following the measurement of the critical current(I_c) distribution along transverse dimension of the tape, a significant disparity in I_c was observed between the edges and the central region of the tape. Microstructure wise, several typical defects were identified at the edges: 1) REBCO layer on the surface decomposed into some flower-like formations with a radius of about 100 μm; 2) several buffer layers expanded, presenting an arch-like structure, which led to a varying orientation of REBCO phases on the top. The helical travelling of the tape causes uneven tension along the transverse dimension, which affects difference thermal contact. This would result in a considerable temperature difference between the edge and the center of the tape. This study offers valuable insights for enhancing the transverse uniformity of tapes deposited by reel-to-reel manner, paving the way for future improvements in the production of REBCO tapes.

Acknowledgment

This work was financially supported by the National Key R&D Program of China of National Natural Science Foundation of China (Grant No. 2022YFE03150201), the National Natural Science Foundation of China (Grant No.52277027). The authors would like to acknowledge Professor Satoshi Awaji, Associate Professor Yuji Tsuchiya and Assistant Professor Tatsunori Okada from Tohoku University for their invaluable assistance with I_c distribution measurement conducted at 77 K.

Figure 1. (a) the I_c distribution along transverse dimension (b) the cross-sectional TEM image at the edge of tape (c) the SEM image of REBCO layer at the edge

Keywords: High-temperature superconductor, Pulsed laser deposition, homogeneity along width, Structure