Mechanical Strength Evaluation of a Yoroi-Coil Structured Non-Circular REBCO Pancake Coil in High Magnetic Field

In order to achieve a high intensity and compact multifunctional air-core cyclotron, the behavior of non-circular coils in a high magnetic field at 4.2 K were investigated. Two types of isosceles triangle shaped double-pancake coils: a coil with reinforcement by Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structuring and a coil without reinforcement, were manufactured and their behaviors were observed when current was applied to each coil in a high magnetic field. The non-reinforcement coil showed in 10 T external magnetic field that the superconducting properties of the coil were partially lost and a voltage generated in the coil winding was observed when the applied current exceeded 160 A. After disassembling this coil, it was found that the superconducting tape in the coil winding was plastically deformed and permanently bent at the corners. The reinforced coil due to Yoroi-coil structuring was powered up to the coil current of 300 A in a magnetic field of 14 T. A voltage of 0.3 mV was observed when the coil current was 277 A, and the excitation was terminated when the voltage reached 0.6 mV at 300 A. The coil winding, after the current flowing up to 300 A in 14 T field, indicated that the deformation of it was significantly limited. It was confirmed that the Yoroi-coil type structural reinforcement, even for triangular coils, has sufficient mechanical strength under the conditions of our air-core cyclotron.