UNIVERSITY OF CALIFORNIA

Acoustic Emission Characterization in Superconducting Magnet Quenching Arnaldo Rodriguez-Gonzalez Instrumentation Meeting Presentation September 11 th, 2015

Background Superconducting magnets are ubiquitous in nearly every high- energy accelerator on the planet. Zero electrical resistivity -> higher current density -> higher field -> better bending/focusing. Thermal perturbations can briefly make a local section of magnet go into the normally resistive state. Huge current densities lead to huge power dissipation in the magnet; thermal conduction triggers runaway quantum phase transition (quench). Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting3 An example of quench: I o =160 A (70% I c ), 37 K YBCO superconductor Conduction-cooled, nearly adiabatic situation T peak = 450 K in 2 sec 50% I c degradation Mbaruku et al., IEEE Trans. Appl. Supercond , (2007) A meltdown in an LHC main bending magnet due to a quench. J. Schwerg, PhD thesis, 2010

Section 1: Berkeley Lab Mission SUBTITLE HERE IF NECESSARY Acoustic emissions from quenches Passive The majority of quenches are caused by transient mechanical phenomena (cracks, slip-stick, etc.) These events should generate distinct elastic waves in the magnet infrastructure that can be picked up through an acoustic receiver. Active A hot spot in the magnet will generate thermal strains & stresses, along with material property changes. All of these should contribute to modulating an oncoming elastic wave. Ultrasonic testing should allow us to observe a quench directly and counteract its propagation. Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting4

Objectives Passive Find a consistent acoustic fingerprint for quench-trigger events. Characterize each signal based on the event type (what does a slip-stick look like?). Obtain a spectral quantifier that lets us know where the event occurs and improve the current quench localization method (arrival time). Active Study the effect of cable periodicity windings on the acoustic transmission function. Understand how an active ultrasound signal is altered by a thermal quench event. Find a suitable probe frequency that is not heavily damped but also does not trigger quenching in the magnet. Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting5

Mathematical approach Magnet infrastructure is highly complex. Multiple materials Multiple length scales Finite element analysis is well- suited for our task. Initial modal analysis would give us the eigenfrequencies/eigenmodes of the structure. A local displacement/force would then show relative excitation between these modes/frequencies for passive detection methods. Coupled-field thermomechanical simulation can show ultrasound signal modulation directly through harmonic response & thermal quench models. Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting6

Experimental approach Acoustic tests are planned on an upcoming CCT3 test magnet mandrel (and the full magnet as well). Ring the magnet, then measure local response with piezoelectric sensor distribution or capacitive probes. These tests are critical for understanding the role of damping and validating the finite element model. Experimental methods are being tested on used mandrel sections. Obtained results should be equivalent or comparable to data from the mathematical model. Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting7

Current progress Mathematical Working on identifying thin and thick-rib oscillation frequencies through modal analysis; thin ribs are in the 4-5 kHz range. Local time-domain input + frequency-domain output = requires custom analysis methods. Identifying thickness vs. θ function to generate rib-only model. Experimental Verify whether rib ringing frequencies match the model’s. Observing spectral differences between top & side ribs on the test mandrel section. Learning how to operate piezoelectric sensor and capacitive probes. 8Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting

Current progress Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting9 Example thick-rib signalExample thin-rib signal Harmonic of the 3.25 kHz peak?

Questions? Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting10

References O. Tsukamoto, J.F. Maguire, E.S. Bobrov, and Y. Iwasa, Identification of quench origins in a superconductor with acoustic emission and voltage measurements", Appl. Phys. Lett. 39, 172 (1981) O. Tsukamoto and Y. Iwasa, “Sources of acoustic emission in superconducting magnets”, J. Appl. Phys. 54, 997 (1983). O. Tsukamoto and Y. Iwasa, “Acoustic emission triangulation of disturbances and quenches in a superconductor and a superconducting magnet”, Appl. Phys. Lett. 40, 538 (1992) Y. Iwasa, “Mechanical Disturbances in Superconducting Magnets-A Review”, IEEE Trans on Magn., (1992) H. Lee et al., “Detection of ‘Hot Spots’ in HTS Coils and Test Samples With Acoustic Emission Signals”, IEEE Trans. Appl. Supercond. 14, 1298 (2004) O. Tsukamoto and Y. Iwasa, “Correlation of acoustic emission with normal zone occurrence in epoxy impregnated windings: An application of acoustic emission diagnostic technique to pulse superconducting magnets”, Appl. Phys. Lett. 44, (1984) T. Ishigohka et al., “Method to detect a temperature rise in superconducting coils with piezoelectric sensors”, Appl. Phys. Lett. 43 (3), pp (1983) A. Ninomiya et al., “Quench detection of superconducting magnets using ultrasonic wave”, IEEE Trans. Magn. 25, v2 pp (1989) O. Tsukamoto and Y. Iwasa, “Correlation of acoustic emission with normal zone occurrence in epoxy impregnated windings: An application of acoustic emission diagnostic technique to pulse superconducting magnets”, Appl. Phys. Lett. 44, (1984) T. Ishigohka et al., “Method to detect a temperature rise in superconducting coils with piezoelectric sensors”, Appl. Phys. Lett. 43 (3), pp (1983) A. Ninomiya et al., “Quench detection of superconducting magnets using ultrasonic wave”, IEEE Trans. Magn. 25, v2 pp (1989) Arnaldo Rodriguez-Gonzalez, Sept. 11th Instrumentation Meeting11