Cryogenic testing of microphones and preamplifiers for MEMS quench detection in superconducting magnets

High Temperature Superconducting (HTS) tapes are needed for high field magnets in high-energy physics and nuclear fusion. However, quench events, in which the superconductor loses its superconductivity, can cause significant and costly damage to the device if allowed to propagate. Consequently, rapid quench detection methods are crucial. Existing methods such as voltage taps can be less effective in HTS applications, as the normal zone propagation velocities of HTS devices are slow, drastically increasing quench detection time (Iwasa, Cryogenics, 2003). We propose an alternative method that utilizes a linear array of MEMS microphones embedded in the cryogenic coolant channel (Takayasu, IEEE Transactions on Applied Superconductivity, 2019). The system requires amplifiers and acoustic sensors capable of operation at cryogenic temperatures as low as 4.2 K, although operation at 20 K may be sufficient. We report on cryogenic testing of the Vesper microphone preamplifier ASIC, as well as opamp based preamplifiers using the OPA838, LT1464, AD8591, and AD8057 ICs. The amplifiers are being used with the Vesper VM4 MEMS microphone to achieve acoustic measurements in gaseous helium at temperatures as low as 8 K. A charge amp scheme using the AD8591 achieved the best results to date. [Support from DOE STTR DE-SC0019905.]