We have been developing the HTS magnet system for the “skeleton cyclotron accelerator” as a next generation medical application [1]. This skeleton cyclotron accelerator can stably produce a-ray radionuclides for a targeted a-particle cancer therapy. To install at a hospital, it should be compact, light-weighted, and highly powerful. Therefore, it has no core for the purpose of field forming or stray-field shielding, and the magnet is wound with Rare-Earth Barium Copper Oxide (REBCO) coated conductors. Due to no core, the output energy for radio isotope (RI) production is changeable for multi medical purposes.

We have before developed the 5-H (High thermal stability, High current density, High mechanical strength, High field & compactness, and Highly precise field) technology to enhance the REBCO coil properties. In the 5-H project, we developed the YOROI structure which enhances the mechanical property of REBCO coils by surrounded with stainless steel cases [2]. The pertial element equivalent model was proposed to investigate the thermal stability of no-insulation (NI) REBCO coils [3]. In addition, the screening current simulation method was also developed, and its validity was checked comparing with measurements [4]. These developments are needed for achievement of 5-H technology.

Utilizing the 5-H technology, we are undergoing to manufacture the “ultra-baby” skeleton cyclotron HTS magnet, which is miniaturized with a field of ~1.6 T (3 MeV). The purpose of the miniature development to investigate the feasibility of generating an accurate isochronous field. So far, we have completed the design of “ultra-baby” HTS magnet system. The screening current effect was investigated in simulations. The stress/strain of a non-circular (triangle) coil which was a sector coil to generate the azimuthally varying field was measured in experiments.

We will report the progress of HTS magnet development for skeleton cyclotron accelerator.

This work was supported in part by a Grant-in-Aid for Scientific Research (S) under Grant 18H05244 from the Ministry of Education, Science, Sports, and Culture.

[1] Ueda H, et al., 2019 Conceptual Design of Compact HTS Cyclotron for RI Production IEEE Trans. Appl. Supercond. 29 4101105
[2] Ueda H, et al., 2021 Numerical Evaluation on Electromagnetic and Thermal Stresses in Non-Circular REBCO Pancake Coils of Multi-Coil System For Skeleton Cyclotron IEEE Trans. Appl. Supercond. 31 4603705
[3] Onoshita H, et al., 202 Influence of Coil Size and Operating Temperature on the Transient Stability of a Multi-Stacked No-Insulation REBCO Pancake Coil System IEEE Trans. Appl. Supercond. 30 4702605
[4] Ogata T, et al., 2021 Numerical Evaluation of Screening Current-Induced Magnetic Field Considering Variable Output Energy in REBCO Coil System of Skeleton Cyclotron for Cancer Therapy IEEE Trans. Appl. Supercond. 31 4400105

Keywords: HTS cyclotron accelerator, REBCO magnet, RI production