We have been developing an air-core cyclotron accelerator, named “Skeleton Cyclotron Accelerator,” for the purpose of a next-generation medical application. Mass production of short-lived alpha-emitting nuclei such as At-211 and Ac-225 is desired for a targeted α-particle cancer therapy (TAT). A compact, light-weighted, and high intensity accelerator is required to be developed, since it is installed in a hospital. Due to air-core, the skeleton cyclotron accelerator has a unique character of variable energy and multiparticle acceleration to produce radioisotope (RI) for PET, TAT and other theranostics applications. We have previously investigated a magnetic field necessary for the cyclotron, that is composed by an isochronous and azimuthally varying field, and developed a design method of high field coils wound with Rare-Earth Barium Copper Oxide (REBCO) coated conductors.

We have also developed the 5-H (High thermal stability, High current density, High mechanical strength, High field & compactness, and Highly precise field) technology to maximize the REBCO characteristics. In the 5-H project, we have investigated the YORI reinforcement which can protect REBCO coils from a high electromagnetic force by surrounding the coils with stainless steel cases. The screening current induced fields were numerically investigated the effect on the beam trajectory.

To confirm the validity of the developed technologies, we designed a miniaturized REBCO magnet, called “ultra-baby” skeleton cyclotron HTS magnet. In addition, the stress/strain of a non-circular (triangle) coil which was a sector coil to generate the azimuthally varying field was previously measured in experiments. As the next step, we are now manufacturing “ultra-baby” cyclotron HTS magnet system. In this fall, we will measure the magnetic field map on the mid-plane where particles are accelerated. In our presentation, the field accuracy and the stress/strain profiles are shown as a progress of the development of skeleton cyclotron accelerator.

Keywords: HTS magnet, Cyclotron Accelerator