Fiber-Optics Quench Detection Schemes in HTS Cables for Fusion Magnets

In this article, we report the results from two test campaigns conducted to evaluate the feasibility of implementing a commercially available optical fiber-based distributed sensing technology for Quench Detection (QD) purposes. We successfully characterized the temperature response and sensitivity achievable by this technique when using a bare single mode fiber within a cryogen free cooling system operating in the temperature range from 4 K to 300 K. A fiber was also incorporated into a sample featuring an High-Temperature Superconductor (HTS) stack mounted onto an extruded Aluminum slotted-core cable. Quench-like events were triggered by locally lowering the critical current using the magnetic field produced by a set of permanent magnets placed near the center of the stack. The experiments were carried out at 77 K by cooling the sample through the central channel of the Aluminum core with a forced flow of liquid nitrogen. The test results indicate the viability of this technology as a suitable alternative for QD in long-length HTS cables and motivate further work to develop distributed sensing systems able to work in the conditions foreseen for HTS fusion coils.