Training free superconducting bobbinless solenoid

A bobbinless superconducting solenoid has been constructed, and successfully excited without training up to the critical current of the conductor. The central field was 5.86 T at the maximum overall current density of 300 A/mm2. The inner diameter of the windings is 19.0 cm. the outer diameter is 23.4 cm, and the length is 26.7 cm. The conductor is a NbTi/Cu keystoned compacted strand cable, of which the critical current is 4.6 kA at 6.3 T and 4.2 K. The magnet consists of two layers, namely 345 turns of edgewise windings, and a GFRP outer cylinder and two sheets of cooling channel between them. It has no metallic part except the superconducting cable, therefore it is suitable to pulsed operation. Local wire movement was reduced in this magnet, which is considered to cause training. However, the magnet deformed elastically during excitation. The strain of the windings in axial and circumferential directions, and the voltage oscillation synchronizing with the mechanical vibration of the magnet were measured. The thermal stability of the magnet was examined. The finite element analysis was performed. These results are reported. (Kako, I.)