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

Abstract

Fusion magnets made from high temperature superconducting ReBCO CORC® cables are typically protected with quench detection systems that use voltage or temperature measurements to trigger current extraction processes. Although small coils with low inductances have been demonstrated, magnet protection remains a challenge and magnets are typically operated with little knowledge of the intrinsic performance parameters. We propose a protection framework based on current distribution monitoring in fusion cables with limited inter-cable current sharing. By employing inverse Biot-Savart techniques to distributed Hall probe arrays around CORC® Cable-In-Conduit-Conductor (CICC) terminations, individual cable currents are recreated and used to extract the parameters of a predictive model. These parameters are shown to be of value for detecting conductor damage and defining safe magnet operating limits. The trained model is then used to predict cable current distributions in real-time, and departures between predictions and inverse Biot-Savart recreated current distributions are used to generate quench triggers. The methodology shows promise for quality control, operational planning and real-time quench detection in bundled CORC® cables for compact fusion reactors.

A 6-around-1 cable using high-temperature superconducting STAR ® wires for magnet applications

“…The first is a circuit model following the previous work [25,36,[39][40][41][42][43]. Each star ® wire was represented by a termination resistance, a nonlinear voltage source, and a self inductance.…”

Quench protection for high-temperature superconductor cables using active control of current distribution

“…Another positive consequence of current balancing was that the voltage drop implies that, on average, current flow through the brass spacer is also reduced, yielding reduced heat dissipation in the assembly. The shown in figure 11(b) current redistribution between individual HTS conductors can be readily used to detect an onset of tape resistance, analogously to the earlier proposed Hall sensor-based quench detection method [17,18] also based on detecting the current imbalance. Furthermore, in the future, the current variation data, together with the in-situ measured current-voltage characteristics, may be fed into the real-time field-programmable gate array (FPGA)-based hardware implementing the network model and providing continuous tape voltage estimates.…”

“…At the same time, an algorithm solving for power dissipation in cable components will generate the output for the active controls aimed at reducing the dissipated power. The algorithm could be based on real-time solving of a network model for the multicomponent cable system on a microprocessor or FPGA, as discussed in [18], and further speed-enhanced by a machine learning component that is pre-trained on a set of the network model solutions.…”

“…The limited current sharing challenges quench protection when a hot spot appears in one of the components, and no current can bypass it locally through sharing with the neighboring component. At the same time, it also brings opportunities for implementing new quench detection approaches, such as those based on measuring the current imbalance between components at terminations [17][18][19], enabling access to intricate details of current re-distribution within the cable prior to the quench that is otherwise unavailable to other detection techniques that monitor the HTS cable as a single entity. As these novel detection techniques mature, it becomes increasingly evident that adding a capability of actively modifying current distribution in addition to passively measuring them can bring substantial advantages for cable diagnostics, improve quench protection, and broaden operational stability margins.…”

Review of commercial nuclear fusion projects

“…Moreover, the best arrangement of HTS tapes in cables and then in coils and magnets is an open field of research (Uglietti, 2019) and different solutions are explored for different fusion projects. Another crucial issue that is the focus of an intense research activity is that of magnet quench (Heller et al, 2019;Wolf M. J. et al, 2019;Zappatore et al, 2020;Bykovskiy et al, 2022;Teyber et al, 2022): in fact, a thermo-magnetic instability can lead to a permanent damage to the system.…”