Localization of Quenches and Mechanical Disturbances in the Mu2e Transport Solenoid Prototype Using Acoustic Emission Technique

Abstract

Acoustic emission (AE) detection is a noninvasive technique allowing the localization of the mechanical events and quenches in superconducting magnets. Application of the AE technique is especially advantageous in situations where magnet integrity can be jeopardized by the use of voltage taps or inductive pickup coils. As the prototype module of the transport solenoid (TS) for the Mu2e experiment at Fermilab represents such a special case, we have developed a dedicated six-channel AE detection system and accompanying software aimed at localizing mechanical events during the coil cold testing. The AE sensors based on transversely polarized piezoceramic washers combined with cryogenic preamplifiers were mounted at the outer surface of the solenoid aluminum shell, with a 60 • angular step around the circumference. Acoustic signals were simultaneously acquired at a rate of 500 kS/s, prefiltered and sorted based on their arrival time. Next, based on the arrival timing, angular and axial coordinates of the AE sources within the magnet structure were calculated. We present AE measurement results obtained during cooldown, spot heater firing, and spontaneous quenching of the Mu2e TS module prototype and discuss their relevance for mechanical stability assessment and quench localization.

Feasible voltage-tap based quench detection in a Ag/Bi-2212 coil enabled by fast 3D normal zone propagation

“…However, such a low detection threshold can easily be confused with the often-seen voltage spikes caused by the mechanical motions of the coil such as stick-and-slip. Therefore for the mullite coil, the effectiveness of quench detection using voltage taps is severely compromised, consistent with the usual concern that quench detection in coils made from high-temperature superconductors can no longer rely on voltage taps [13,14] and more advanced but more complex and perhaps also currently less reliable methods such as fiber optics [15] or acoustic emission [16,17] need to be developed. As a result, the coils will be restricted to working at low operating current density regions as it becomes increasingly more dangerous to work at high operating current density regions, despite the fact that wire J E of up to 1000 A mm −2 is becoming available in REBCO-coated conductors [4] and Bi-2212 round wires [3].…”

Mu2e Transport Solenoid Prototype Tests Results

“…Another small fraction of the heater power is taken away by the efficient cooling system of this magnet. These heaters were also used for the verification of quench localization using acoustic emission technique [11].…”

CORC $^{\circledR}$ cable terminations with integrated Hall arrays for quench detection

“…If a heat source is sufficiently powerful to locally transition the conductor, these properties are no longer advantageous and catastrophic levels of energy can be dissipated before the slow-moving quench wave is detected with traditional techniques. Numerous methods have been explored to supplement voltage measurements in detecting normal zone transitions, including optical fibers [8,9], acoustic emission monitoring [10,11], stray capacitance monitoring [12], diffuse ultrasound thermometry [13][14][15], quench antennas [16][17][18] and Hall sensors [19], to name a few. Promising results have been reported, although few are non-invasive and provide real-time quench protection.…”