SMART conductor on round core (CORC®) wire via integrated optical fibers

Abstract

Superconducting cables based on high temperature superconductors (HTS) are necessary for applications requiring large currents and low inductance, such as compact fusion reactors. In this paper, we report the proof-of-concept of a SMART Conductor on Round Core (CORC®) wire realized via integration of optical fibers into the copper core. A SMART CORC® wire with integrated optical fibers was manufactured and its capabilities have been experimentally demonstrated. Results show that by interrogating the optical fibers via Rayleigh backscattering, a Spectral Shift signal as a function of time and position along the cable can be used to detect and locate hot-spots that are developed within the wire or its terminations. It has been found that highly localized current injection into the terminations could initiate hot-spots within the cable at locations where current redistribution between tapes occur. This effect is virtually eliminated when adequate current connections are used that inject current evenly along the cable terminations. Normal zone propagation velocities have been calculated as a function of time using Spectral Shift data for a heater-induced quench as well as a quench induced by overcurrent. In both cases the normal zone propagation velocity was about 6 cm s−1, but in the heater-induced experiment it was preceded by 500 ms of slower propagation at 2.5 cm s−1.