Spatial and temporal resolution requirements for quench detection in (RE)Ba₂Cu₃O_xmagnets using Rayleigh-scattering-based fiber optic distributed sensing

Abstract

One of the key remaining challenges to safe and reliable operation of large, high temperature superconductor (HTS)-based magnet systems is quench detection and protection. Due to the slow quench propagation in HTS systems, the conventional discrete voltage-tap approach developed for NbTi and Nb 3 Sn magnets may not be sufficient. In contrast, a distributed temperature profile, generated by a distributed temperature sensor and facilitating continuous monitoring of the temperature at any monitored locations within a magnet with high spatial resolution, may be required. One such distributed temperature sensing option is the use of Rayleigh-based fiber optic sensors (FOS), which are immune to electromagnetic interference. The detection of a quench via Rayleigh-based FOS relies on converting the spectral shifts in the Rayleigh scattering spectra into temperature variations. As a result, the higher the spatial sampling resolution the larger the data processing volume, and thus the lower the temporal sampling resolution. So, for effective quench detection, which requires the quick and accurate identification of a hot spot, it is important to find a balance between the spatial and temporal resolutions executable on a given data acquisition and processing (DAQ) system. This paper discusses a method for finding an appropriate DAQ technology that matches the characteristic of a superconducting coil, and determining the acceptable resolutions for efficient and safe quench detection. A quench detection algorithm based on distributed temperature sensing is proposed and its implementation challenges are discussed.

Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

“…Continuous fiberoptic sensors based on Rayleigh scattering [52][53][54] are an attractive alternative to their discreet counterparts, as they allow for both a distributed measurement of temperature along the entire length of superconducting coil winding and for the [44]). (b) A practical implementation of same technique in a form of a Hall array embedded in the current terminals of the CORC ® cable.…”

“…Continuous fiberoptic sensors based on Rayleigh scattering [52][53][54] are an attractive alternative to their discreet counterparts, as they allow for both a distributed measurement of temperature along the entire length of superconducting coil winding and for the precise localization of the developing hot spots. For this technique, thermal sensitivity scales inversely with the probed length of the optical fiber, and thermal sensitivities greater than 7 K/cm [52], as well as a minimally detectable size of the normal zone of less than 5 mm [53], have been reported. It should be noted, however, that distributed optical sensing requires substantial computational power to achieve real-time quench detection in long lengths of HTS conductor.…”

Superconducting accelerator magnet technology in the 21st century: A new paradigm on the horizon?

“…Another proposed technique to monitor and detect quenches in high current REBCO cables is by integration of optical fibers in the cable architecture using Rayleigh-backscattering interrogated optical fibers, resulting in a self-monitoring cable with both strain and temperature sensing capabilities as a function of position along the cable length and in time [59][60][61]. Work to date has been done under carefully controlled experimental conditions but there are plans to explore the technique in a more realistic environment.…”

Quench Detection for High-Temperature Superconductor Conductors Using Acoustic Thermometry

“…Various non-voltage quench detection and localization alternatives were proposed in the past, based on transient variation of stress [9][10][11], magnetic field [12]- [14], and acoustic emission [15]- [18]. More recently, techniques involving interferometry [19], Rayleigh [20]- [23] and Raman scattering [24] in optical fibers, and stray capacitance monitoring [25] specifically aimed at HTS applications were demonstrated. However, all those techniques detect hot spot indirectly: either through mechanical or electromagnetic manifestation, or by relying upon a temperaturedependent property of another body (optical fiber, liquid cryogen) thermally coupled to the quenching conductor.…”