Experimental and theoretical investigation of mechanical disturbances in epoxy-impregnated superconducting coils. 1. General introduction

A self-monitoring, SMART (RE)Ba2Cu3O7−x (REBCO) conductor has been created by integrating optical fibers into the solder fillet of the current REBCO conductor architecture. By interrogating the integrated optical fiber by Raleigh backscattering, a spectral shift signal as a function of time and position along the conductor is obtained. Due to the direct integration into the solder fillet, intimate, consistent contact between fiber and conductor is obtained, while the optical fiber is protected and does not take up any space in the magnet winding. Therefore, the SMART conductor enhances the benefits of the co-wound fiber approach and provides ultimate sensitivity and practicality. Several samples of SMART REBCO conductor have been manufactured and characterized. The strain self-sensing capabilities have been demonstrated as well as thermal perturbation detection and localization with 2.56 mm spatial resolution. Results show that a key feature of the SMART conductor concerns its sensitivity to thermal perturbation; unlike in the case of a coil with co-wound optical fiber, the SMART REBCO sensitivity increases as the temperature decreases. A series of quench measurements have been performed, both on straight samples and on a pancake coil, at temperatures as low as 14.6 K. Using the data collected by the SMART REBCO during quench experiments, the temporal evolution of the size of a normal zone and the instantaneous normal zone propagation velocity have been calculated.

https://iopscience.iop.org/article/10.1088/1361-6668/aa8762/pdf

Self-monitoring ‘SMART’ (RE)Ba2Cu3O7−x conductor via integrated optical fibers

High-temperature superconductors (HTS) are being increasingly used for magnet applications. One of the known challenges of practical conductors made with high-temperature superconductor materials is a slow normal zone propagation velocity resulting from a large superconducting temperature margin in combination with a higher heat capacity compared to conventional low-temperature superconductors (LTS). As a result, traditional voltage-based quench detection schemes may be ineffective for detecting normal zone formation in superconducting accelerator magnet windings. A developing hot spot may reach high temperatures and destroy the conductor before a practically measurable resistive voltage is detected. The present paper discusses various approaches to mitigating this problem, specifically focusing on recently developed non-voltage techniques for quench detection.

/pdf/quench-detection-and-protection-for-high-temperature-2s8l0fj2gm.pdf

Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

submitter : Acoustic emission during quench training of superconducting accelerator magnets

In this paper we report results of two series of experiments, one performed on a double-pancake coil wound with Bi2223/Ag tape and the other on coated YBCO samples to demonstrate that an acoustic emission (AE) technique is a promising diagnostic tool to detect the presence of a "hot spot" in HTS devices. The AE technique may be used as complement to standard voltage technique to facilitate early detection of the presence of a "hot spot" in HTS devices and thus help to protect the HTS devices from permanent damage.

Detection of 'hot spots' in HTS coils and test samples with acoustic emission signals

Locations of disturbances and quenches in a superconductor and a superconducting magnet have been determined by using a multiple set of acoustic emission (AE) sensors. The letter presents an AE triangulation technique and experimental results.

O. Tsukamoto

Papers

Acoustic emission triangulation of disturbances and quenches in a superconductor and a superconducting magnet