Manoj Thevalappilly Paulose

REBCO tapes exhibit considerable potential for application in high magnetic field devices such as compact fusion reactors and particle accelerators; next-generation electric machines such as high-efficiency industrial motors and high-power wind turbine generators; and electric aircraft. Our group had previously demonstrated an advanced metal organic chemical vapor deposition (A-MOCVD) method to produce 50-meter-long REBCO tapes with film thickness over 4 µm in a single pass, and a uniform critical current (I_c) over 1,750 A/12 mm at 65 K, 0.25 T. Further, for high magnetic field applications, 40-meter-long tapes have been made by A-MOCVD with an I_c over 4,000 A/12 mm at 4.2 K and 13 T, as well as over 1,400 A/12 mm at 20 K and 20 T. A laminar vapor path design in the A-MOCVD reactor enabled the growth of thick REBCO films with a high precursor-to-film conversion efficiency up to 45% (4x the conversion efficiency of conventional MOCVD of REBCO tapes). Subsequent advancements in the A-MOCVD process enabled simultaneous deposition of REBCO films on both sides of a double-sided buffered substrate, in a single pass. This yielded double-sided, 30-cm-long REBCO tapes with 3.4-µm-thick films on each side, which showed I_c over 530 A/4 mm at 20 K, 20 T. This paper reports our recent work on next-generation A-MOCVD design to scale up double-sided REBCO tapes to long lengths, with superior performance and an increased precursor-to-film conversion efficiency beyond 70%. Tape heating and precursor delivery methods incorporated in the new design aims to facilitate the scale-up of A-MOCVD for multi-track deposition for higher tape throughput.

Rare Earth Barium Copper Oxide (REBCO) superconducting thin films on dielectric substrates are being developed for microwave and radio frequency applications such as transmission lines for quantum computing. Our group previously demonstrated the growth of REBCO thin films on short, flexible, yttria-stabilized-zirconia (YSZ) substrates. In this study, we report high-quality REBCO films on 12-cm-long flexible YSZ substrates. We planarized the surface of 40-µm-thick flexible YSZ substrate by vertical dip coating in n-propanol solution to achieve average surface roughness R _a3 (LMO) cap layer. The out-of-plane and in-plane texture values of the LMO films were 3.9° and 6.9° respectively. REBCO films of a thickness of 350 nm were grown on these 12-cm-long flexible YSZ substrates by metal organic chemical vapor deposition (MOCVD) and a critical current density (J _c) of 1.06 MA/cm² was achieved at 77 K, 0 T. We are also developing an electrically conductive buffer architecture for defect-tolerant REBCO tapes, to shunt current from the REBCO film to substrate. This buffer architecture is based on conductive titanium nitride buffer on Hastelloy C276 substrate, with an oxide cap layer deposited by magnetron sputtering. REBCO films, about 350 nm thick, have been grown by MOCVD on this buffer architecture with a J _c greater than 1 MA/cm² at 77 K, self-field. Texture, microstructure, composition and critical current density of REBCO tapes on electrically conductive buffers will be presented.