Acoustic Sensor Development for Quench Detection in HTS Conductors

A MEMS (Micro Electro-Mechanical System) acoustic sensor-array quench detection method has been proposed for quick, unobtrusive, and precisely localized detection of quench events in superconducting magnets. A cryogenic probe was designed and built to study the quench event in a gaseous coolant induced in a segment of an HTS tape and verify the effectiveness of acoustic MEMS sensors in detecting such events. Prior work characterized the performance of a commercially available Vesper MEMS microphone, and associated amplifiers, in cryogenic conditions which were utilized in this work. Critically, the application specific integrated circuit (ASIC) used to amplify the MEMS piezo-sensor output signal fails to operate at temperatures below 110 K. Thus, the ASIC was removed from the microphone package and replaced with a custom low temperature preamplifier which we have shown performs with no loss of function at temperatures as low as 10 K. The quench experiment is conducted using the probe within a two-stage Gifford-McMahon (GM) cryocooler in a gaseous helium environment, at cryogenic temperatures between 20 K to 60 K. Three temperature sensors within the sample region monitor temperature of the HTS sample tape and environment. The HTS sample, a 2 mm wide REBCO tape, is mounted within a square G10 tube. A linear array of the repackaged sensors is mounted to the tube to detect the quench event. The quench detection behavior using the sensors is compared with the readings from voltage taps on the sample. The response characteristics of the Vesper acoustic piezo-sensor with the newly identified, cryogenic-safe preamplifier in detecting quench events of REBCO tapes in gaseous helium are presented.