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Description
Compact cyclotrons are required to produce radiopharmaceuticals used in targeted alpha-particle therapy, which is a promising treatment for patients with intractable cancers. To realize a compact cyclotron, we have proposed the Skeleton Cyclotron—an air-core compact cyclotron using high-temperature superconducting (HTS) technology. This cyclotron consists of circular and non-circular coils, all wound with REBCO tape using a no-insulation (NI) winding technique. We have fabricated a 1/2-scale REBCO coil system of the Skeleton Cyclotron called the Ultra-Baby Cyclotron, which has a diameter of about 0.7 m (the full-scale Skeleton Cyclotron has a diameter of about 1.6 m). In this experiment, the degradation of the REBCO coil was observed before charging to the target current. The mechanical deformation was confirmed in the degraded REBCO coil. We attribute this to thermal contraction and additional stress due to the screening current. REBCO coils in Ultra Baby Cyclotron are non-impregnated and non-insulated, they are considered susceptible to deformation, such as the formation of gaps between the winding and the external reinforcement after cooling. And numerical calculations show that the screening current circulates in the REBCO windings in excess of the energizing current. In this study, the coil degradation observed in the experiment is verified in terms of stresses due to thermal shrink and electromagnetic force including screening currents.
The part of this work was supported by JSPS Grant-in-Aid for Scientific Research (S) Grant Number 18H05244.
