Large-scale applications of coated superconductors are being increasingly pursued with larger stored energy and tape lengths in kilometre lengths. For small-scale superconducting magnets, the use of voltage taps as a reliable quench protection methodology has been dominant. However, this method is unlikely to be successful for large-scale HTS magnets with much larger stored energy because the electromagnetic environment is noisy and with coated conductors, any localised hot spot is slow to propagate and can rapidly lead to thermal runaway and uncontrolled quench.

To address the need for rapid hot-spot detection in an electromagnetically noisy cryogenic environment, the use of optical fibre sensors has been proposed to measure thermal events rapidly. In this work, we examine the rapid response rate of two classes of optical fibre sensors: discrete Fiber Bragg Gratings (FBGs) and distributed continuous FBGs (cFBG) in the presence of a localised hot spot in a coated conductor tape. In a short sample of high-temperature superconducting tape, we induced thermal pulses ranging from 5 J to 26 J, and we compare the delay between the initiation of the disturbance and the initial temperature response of all sensors under both cryogenic and room temperature conditions. Experiments were repeated with transport current in the conductor in order to investigate quench behaviour.

We present the results of the experimental studies comparing the response time of conventional PT100 temperature sensors, FBG and cFBG. We discuss the implications of applying this rapid (< 500 ms) optical sensing technology as a protection methodology for large-scale magnets.

Keywords: quench, fiber, optical, hts protection