Measurement of Sudden Displacements in Superconducting Coils using Search-coils

Search-coils, which can detect magnetic field variations, have been applied to the measurement of superconducting coil displacements. The advantage of the search-coil is that it can measure displacements which occur in an arbitrary section of a superconducting coil without making contact with a winding. In our experiment, the radial displacements in the straight and curved sections of a racetrack coil were measured and compared through the results of FEM analysis. The results showed that micrometer-order sudden displacements were detected during the ramping of the racetrack coil current, and the sum of sudden displacements increased with the racetrack coil current. When the racetrack coil current reached the maximum value of 1000 A, the total displacement of the straight section was three times greater than that of the curved section. This measured result agrees relatively well with the numerically calculated result.