Locating a Mechanical Disturbance Source in a Superconducting Coil Using Pickup Coils on a Diaphragm

We report a new method using pickup coils on a diaphragm to locate a mechanical disturbance source in a superconducting coil. Pickup coils with a twisted pair cable have a lower heat penetration compared to acoustic emission (AE) sensors with a coaxial cable. Vibrations of the diaphragm, which are caused by an acoustic pressure wave from a mechanical disturbance source, vibrate the pickup coil in an inhomogeneous magnetic field and generate signals in the pickup coils as inductive voltages. We have applied pickup coils to locate the azimuthal position of mechanical disturbance sources which induce superconducting magnet quenching. The azimuth position of the mechanical disturbance sources have been located by measuring the time differences of the acoustic wave arrival at each pickup coil. The results using the pickup coils and AE sensors agreed in the angular range below 38 degrees. The measurement error of this method was caused mainly by the detection time lag due to the acoustic wave damping in the coil windings.