Quench Detection for High-Temperature Superconductor Conductors Using Acoustic Thermometry

Abstract

Abstract-Detecting local heat-dissipating zones in hightemperature superconductor (HTS) magnets is a challenging task due to slow propagation of such zones in HTS conductors. For long conductor lengths voltage-based methods may not provide a sufficient sensitivity or redundancy, and therefore non-voltage based detection alternatives are being sought. One of those is the recently proposed method of Eigen Frequency Thermometry (EFT), which is an active acoustic technique for a fast and non-intrusive detection of "hot spots", utilizing temperature dependence of the conductor elastic moduli. In the present work, we demonstrate efficiency of EFT for detecting localized heating in a 1.2 m-long sample of REBCO tape immersed in liquid nitrogen, and benchmark sensitivity of the acoustic detection with respect to voltage, hot spot temperature, and power dissipation in the conductor. Modifying the original technique for differential mode of operation enables a much improved sensitivity, and adds a hot spot localization capability. Furthermore, we adapt this technique to subscale coils wound with REBCO CORC® conductor built in the framework of US Magnet Development Program. A successful thermal-based detection of dissipation onset at the critical current for a two-layer canted CORC® dipole assembly is discussed. Index Terms-Acoustic sensors, temperature sensors, superconducting coils, high-temperature superconductors, quench detection.

Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

“…Thermal sensitivity is expected to be proportional to ∆t [81], and thus one can benefit from the large mechanical Q-factor of the coil by increasing ∆t further into the "tail" of the coda. Some recent examples of applying this technique for detecting hot spots in HTS conductors are experiments on a HTS tape stack [82], as well as a single ReBCO tape and coils wound with CORC ® cable [83]. A similar waveform monitoring approach was proposed in [84] for the thermal mapping of biological tissues with medical ultrasound.…”

“…(Left) Principle of active acoustic thermometry: diffuse ultrasonic wave (coda) is being monitored for a time shift caused by local temperature variations in the interior of a monitored object. (Right) Demonstration of the active acoustic quench detection in a 1.2 m long ReBCO tape conductor in liquid nitrogen, where time shift associated with a hot spot formation is clearly detected along with the resistive voltage (adopted from[83]).…”

Dipole Magnets above 20 Tesla: Research Needs for a Path via High-Temperature Superconducting REBCO Conductors

“…As part of the USMDP's effort to develop underpinning technology to advance the magnet science, LBNL and collaborators are developing advanced quench detection and diagnostic techniques for HTS magnets. One example is to use the acoustic thermometry to detect quenches that have been successfully demonstrated in REBCO tapes and small coils [166,220]. A promising concept based on the stray capacitance between the coil and its structural elements has also been successfully tested in Bi-2212 racetrack coils in collaboration with CERN [221,222].…”

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

“…Eigen Frequency Thermometry (EFT) is an active acoustic technique that can be used to monitor changes in the elastic modulus of an HTS coil due to temperature changes making the conductor a distributed temperature sensor [58]. Acoustic pulses are transmitted through the magnet by a piezoelectric transducer.…”