Quench detection using Hall sensors in high-temperature superconducting CORC^®-based cable-in-conduit-conductors for fusion applications

Abstract

Advanced magnet systems for fusion applications would greatly benefit from the use of high-temperature superconductors (HTS). These materials allow fusion magnets to operate at higher magnetic fields, allowing for more compact fusion machines, and allow for operation at elevated temperatures, enabling demountable coils that provide access for maintenance of the fusion reactor. Quench detection remains a major challenge in the protection of HTS magnets that are vulnerable to localized conductor burnout due to their low quench propagation velocities. One of the methods explored is the use of Hall sensors that are incorporated in or near the magnet terminations that can detect local field variations that occur as a result of current redistribution within the conductor to bypass a hotspot within the magnet winding. This method is potentially well suited for Cable in Conduit Conductors, such as those made from Conductor on Round Core (CORC) cables, in which sub-cables containing HTS tapes are connected to the terminations at a low resistance. To demonstrate the technique, a CORC® triplet consisting of three sub-cables, rated for 4 kA operation at 77 K, was manufactured and Hall sensors were used to measure local field variations next to the terminations due to current redistribution between the cables. The Hall response was compared to voltages that developed over the cables and terminations as a local hotspot was applied to different cables in the triplet. It was found that the Hall sensors were faster and more sensitive than voltage contact measurements and were able to reliably detect current redistribution of only a few amperes caused by a hotspot, well before the triplet exceeded its critical current. The method also allowed the detection of heater-induced hotspots during high ramp rates of 2 kA s−1 relevant for fusion applications. Hall sensors have a distinct benefit of being less sensitive to inductive pickup of AC interference compared to voltage contact measurements that make quench detection through voltage measurements in magnets especially challenging. The method can also be used for diagnostic measurements of current redistribution caused by other sources such as inhomogeneous current injection from faulty joints, or localized conductor damage. The Hall sensors are likely capable of detecting the onset of a quench that may occur a far distance away from the sensor location, presenting a breakthrough in HTS quench detection that potentially removes one of the remaining barriers to reliable operation of large HTS magnet systems.

Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

“…However, in a case where several individual CORC ® conductors are used to form a cable (cable-in-conduit geometry), the approach is expected to be efficient for any practical length. This has been recently demonstrated experimentally [46]. Further experiments aimed at justifying this approach for long lengths of HTS cable are currently in progress.…”

Current distribution monitoring enables quench and damage detection in superconducting fusion magnets

“…The methodology relies on the ability to predict current distributions in CICC with limited inter-cable current sharing, that applies to CORC ® CICC concepts such as the ribbon CICC 26 and 6-around-1 10 shown in Fig. 1 .…”

“…This can be used to identify a poor joint or conductor damage; this is of importance for quality control in fusion magnets. Using the previously published data of Weiss et al 26 , the trained model is then used to predict CICC current distributions, and departures between predictions and inverse Biot-Savart recreated current distributions are used to generate quench triggers.…”

“…Finally, the quench detection capabilities are presented using the previously published three-cable Ribbon CICC of Ref. 26 at 2000 A/s.…”

Advancing Superconducting Magnet Diagnostics for Future Colliders

“…In addition to identifying defects, such knowledge facilitates real-time monitoring and predictive operation where improved high-speed modeling tools capable of near-real-time prediction are desired; fault triggers can be generated when magnet measurements depart from model predictions. This "hardware-in-loop" magnet operation scheme relies on continued improvements in diagnostics aimed at probing current distributions in real time [13,[34][35][36], which can be considered for both inter-tape redistribution in single cables (Fig. 3) and for inter-cable redistribution in cable bundles (e.g.…”