Heavy-ion radiotherapy is treating the cancer by irradiating energetic carbon beams, and it has a high curative effect. It can also have an attractive physical characteristic called “Bragg Peak” which enables a high dose to be administered to the deep-seated tumor while limiting the dose to the surface of the patient's body. For that reason, it's becoming more widespread, and many patients have been treated with this heavy-ion radiotherapy. However, accelerator system such as a synchrotron was required to accelerate ions. It is too large to install such accelerator in a general hospital, so that it is necessary to reduce the size of the particle radiotherapy to deliver this treatment to more patients, there is a need for a compact heavy ion radiotherapy device that can provide advanced treatment.

Therefore, a project to develop a compact heavy-ion radiotherapy system, the “Quantum Scalpel” project, was started at National Institutes for Quantum Science and Technology (QST). One of the aims of this project is to reduce the footprint of synchrotron by applying superconducting technology, and we have been developing a superconducting magnet for this system in collaboration with QST. This compact superconducting synchrotron can accelerate the carbon ion up to the maximum energy of 430 MeV/u in 5 seconds. After acceleration, the carbon ions are gradually decelerated and extracted with an energy step of about 600 for the medical irradiation. The circumference of the synchrotron ring is about 29 m which is roughly half the circumference of the conventional rings for heavy-ion therapy and, the ring consists of four 90-degree superconducting magnets. The superconducting magnet has a curved structure and is composed of a pair of the 45-degree combined-function superconducting magnets, which can provide both dipole and quadrupole fields. The maximum dipole field and quadrupole field were designed to 3.5 T and 1.5 T/m, respectively. The magnet is operated at a high speed of 0.64 T/s. Although such high-speed excitation generates large AC losses, a conduction cooling method using 4K GM cryocooler was adopted to achieve easy operation.

Design studies and prototyping test on this superconducting magnet have been carried out, and in March 2023, the manufacturing contract related to the “Quantum Scalpel” project was signed and the manufacturing of the superconducting synchrotron was started. This presentation will be reported on recent progress of this project and the development of a superconducting magnet for the compact synchrotron.