Spatial modulation of Joule losses to increase the normal zone propagation velocity in (RE)BaCuO tapes

Abstract

This paper presents a simple approach to increase the normal zone propagation velocity in (RE)BaCuO thin films grown on a flexible metallic substrate, also called superconducting tapes. The key idea behind this approach is to use a specific geometry of the silver thermal stabilizer that surrounds the superconducting tape. More specifically, a very thin layer of silver stabilizer is deposited on top of the superconductor layer, typically less than 100 nm, while the remaining stabilizer (still silver) is deposited on the substrate side. Normal zone propagation velocities up to 170 cm/s have been measured experimentally, corresponding to a stabilizer thickness of 20 nm on top of the superconductor layer. This is one order of magnitude faster than the speed measured on actual commercial tapes. Our results clearly demonstrate that a very thin stabilizer on top of the superconductor layer leads to high normal zone propagation velocities. The experimental values are in good agreement with predictions realized by finite element simulations. Furthermore, the propagation of the normal zone during the quench was recorded in situ and in real time using a high-speed camera. Due to high Joule losses generated on both edges of the tape sample, a "U-shaped" profile could be observed at the boundaries between the superconducting and the normal zones, which matches very closely the profile predicted by the simulations.