Quench Detection Method for Large Superconducting Magnets using Robust MEMS Acoustic Sensor Arrays

High Temperature Superconducting (HTS) materials have excellent mechanical and electrical properties that are attractive for various applications such as power cables and high field, high current superconducting magnets, particularly playing a key role in the commercialization of fusion energy machines. However, HTS materials have very slow normal zone propagation velocities (NZPV) (2-3 orders of magnitude lower) compared with Low Temperature Superconductors. Therefore, it is critical to develop a reliable Quench Detection (QD) and magnet monitoring system for HTS magnets. We propose to develop a new, low-cost, low-power-consumption method to detect a quench in a superconducting magnet utilizing an acoustic/pressure sensor technique based on micro-electro-mechanical system (MEMS) sensors. The method uses acoustic MEMS sensors, built into a sensor array, to allow detection and diagnosis of abrupt changes of a superconductor in real time. This technique allows for an accurate identification of the location of the incident. The QD proposed will be particularly attractive for fusion magnet Cable In-Conduit Conductors (CICC) made with HTS, such as Rare Earth Barium Copper Oxide (REBCO) tapes. The sensor array is installed in a channel along the superconducting cable and detects a quench by sensing the abrupt conductor temperature changes which produce an acoustic signature propagating in the coolant. The team evaluated experimentally commercial MEMS sensors and amplifiers for low temperature operation (to 12K). A test bed for quench detection was constructed and a single MEMS microphone on a REBCO tape in LN2 demonstrated a strong response to an induced quench event, validating the performance of the MEMS sensor approach for QD. System topologies and signaling were explored for use in a notional MEMS-based quench detection arrayed system for toroidal field magnets of a Fusion Tokamak. We will develop MEMS sensors, functionally-integrated with conditioning electronics and packaging, and deploy into an array system to demonstrate quench detection, tested with REBCO cables. The goal of this program is to demonstrate the proposed MEMS QD technology and show it is suitable for QD of HTS superconducting magnets operating in cryo-fluids. The proposed MEMS sensor array QD and superconductor monitoring method will not only be applicable to CICC large fusion magnets made but, due to its low-cost and low-power, will have broader applicability across a variety of magnet devices such as: compact synchrocyclotrons, MRI, NMR, SMES, transformers, fault current limiters and generators, accelerator magnets, as well as electric power transmission superconducting cables.