REBCO coated conductors are now in mass production as unique practical wires available for emerging high field or liquid helium free applications. Although various manufacturing methods have been proposed, the IBAD/PLD method, which has been studied since the inception of coated conductors, is currently the most widely used for those high field applications such as high-end NMR systems and "compact" nuclear fusion, etc., which could not be achieved by LTS wires such as Nb3Sn [1].
Pulsed laser deposition (PLD) is a non-equilibrium vapour process characterised by a high growth rate under largely supersaturated conditions, though it also has excellent controllability of varied deposition conditions for complex multi-element oxide films even at sufficiently high oxygen pressure. It allows the production of stable conductors with high in-field performance, with densely dispersed pinning centres in sharply textured REBCO films growing at extremely high rates, also with high yield due to its high reproducibility, resulting in sufficient mass production throughput.
In order to improve the longitudinal uniformity and lot-to-lot variation of these optimised process conditions, we had designed and developed "hot-wall" reel-to-reel PLD equipment, which achieved quite robust and reproducible temperature uniformity by means of a furnace-like heating system [2]. We have succeeded in commercialising long length and uniform REBCO wires including BaHfO3 nanorods and have developed the productivity of these wires towards cost reduction without compromising quality control and uniformity for long piece length. It has also allowed us to expand the variety of wire widths to ensure sufficient single length conductors. We currently offer lineups of BaHfO3 doped EuBaCuO wires and undoped GdBaCuO wires in widths from 2mm to 12mm. Additional improvements are undergoing to explore further productivity, piece length, and quality of transporting and mechanical strength.
We are now expanding production capacity with Hot-Wall PLD. Although scale-up costs associated with UV pulsed lasers are unavoidable, they are decreasing and now acceptable enough to achieve mass production of affordable REBCO wires with reliable enough quality and throughput.
[1] P. Wikus, et.al., "Commercial gigahertz-class NMR magnets", Supercond. Sci. Technol. vol. 35, Art. no. 033001, (2022)
[2] Y. Iijima, et.al., "BMO-Doped REBCO-Coated Conductors for Uniform In-Field Ic by Hot-Wall PLD Process Using IBAD Template", IEEE Trans. Appl. Supercond.,vol. 27, no. 4, Art. no. 6602804, (2017)
A part of this work is based on results obtained at the High Field Laboratory for Superconducting Materials, IMR, Tohoku University.
Keywords: REBCO coated conductors, IBAD, Hot-Wall PLD, BaHfO3 BMO doped REBCO