Measurements of Magnetic Field Harmonics in Superconductor Coil Wound by Surface Winding Technology

Magnetic field harmonics (multi-pole component of magnetic field) were measured in a 24-layer coil for a dipole magnet wound with NbTi round wires by using the surface winding technology (direct winding technology). The coil was wound layer by layer, and the magnetic field measurements were carried out by using rotating pick-up coil system, when the 4 layers, 10 layers, 16 layers, 20 layers, and 24 layers of the coil were wound. The measured magnetic field harmonics were compared with theoretical values. The error, which is the difference between the measured value and theoretical one, does not increase substantially with increasing number of wound layers when measured at the center of the coil. Larger errors measured near the coil end should have been caused by the position errors of wires, which was observed visually.