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

High Temperature Superconducting (HTS) materials have excellent mechanical and electrical properties. They are very attractive for various industrial applications such as power cables and high field, high current superconducting magnets. Magnets made with these materials could play a key role in the commercialization of fusion energy machines. However, HTS materials have very slow normal zone propagation velocities (NZPV) compared with practical Low Temperature Superconductors (LTS) such as NbTi and Nb3Sn. NZPV is 2-3 orders of magnitude lower in HTS compared to LTS. Therefore, it is critically important to develop a reliable quench detection 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. In addition, this technique allows for an accurate identification of the location of the incident. The quench detection proposed will be particularly attractive for fusion magnet Cable In-Conduit Conductors (CICC) made with high temperature superconductor (HTS) such as Rare Earth Barium Copper Oxide (REBCO) tapes. The array of acoustic sensors 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 (gas or liquid). During Phase-I, the proposed acoustic sensor method will be first evaluated experimentally for HTS tapes and cables using commercially available MEMS sensors. With the experimental results we will investigate and develop an appropriate design of a new or modified MEMS acoustic sensor suitable for quench detection of a superconductor in low temperature cryogenic environments such as liquid nitrogen, helium gas and liquid helium.The proposed quench detection and superconductor monitoring method using a MEMS sensor array will not only be applicable to a large fusion magnet made with CICC cables but will also have broader applicability. Due to its expected low-cost and low-power operation, this quench detection method could be implemented across a wide variety of industrial magnet devices such as: compact synchrocyclotrons, MRI, NMR, SMES, transformers, fault current limiters and generators, accelerator magnets including dipoles, quadrupoles, and corrector magnets, as well as for electric power transmission superconducting cables.