Acoustic emission monitoring results from the MFTF magnets

A technique for monitoring disturbances using acoustic emission (AE) in superconducting magnets was applied to the superconducting yin-yang magnet pair for the Mirror Fusion Test Facility (MFTF-B) at the Lawrence Livermore National Laboratory (LLNL). Signals from twelve AE sensors mounted on the magnet were recorded during magnet charging tests.A minicomputer-based signal processing technique was then developed for real-time AE event detection, location, and characterization. Acoustic emission events caused by movement of conductors in the energized magnet windings or by structural disturbances such as epoxy cracking and debonding could be identified. The data recorded from the MFTF tests were then analysed.The results showed a wide range of AE activity detected by the sensors. Activity from structure and conductor motion showed different behaviour with increasing magnet current. Sensors mounted in the small radius regions of the magnet exhibited the highest levels of activity, agreeing with analysis of maximum loads and independent magnet voltage monitoring results.