Development of an HTS Accelerator Magnet With REBCO Coils for Tests at HIMAC Beam Line

An R&D project funded by the Japan Science and Technology Agency under its S-Innovation Program is currently in progress. The purpose of this project is to develop fundamental technologies for accelerator magnets with REBCO coils. In the first step of this project, winding technology for fabricating REBCO coils required for HTS accelerator magnets was developed. At the last stage of this project, there are plans to fabricate cryocooler-cooled REBCO magnets and evaluate the beam guiding characteristics and stability against beam injection to the magnets at the beam line of Heavy Ion Medical Accelerator in Chiba (HIMAC). This paper describes the design of an HTS magnet fabricated for this evaluation and presents fabrication results of this magnet. The magnet had a room-temperature beam duct with dimensions 264 × 40 mm for beam guiding. The magnet consisted of a pair of racetrack coil stacks each containing four coils, and a cold iron was adopted to increase the magnetic field strength. It could generate a dipole field of 2.4 T at the beam duct by 200 A excitation. Furthermore, beam windows were placed on the side of the cryostat for beam injection tests, allowing the beam to irradiate the REBCO coil directly.

I. Introduction

Particle radiotherapy treats cancer by irradiating tumors with accelerated ions, and it has been shown to have a high curative effect and can also reduce the burden on patients. For these reasons, particle radiotherapy is becoming more widespread, and the total number of patients treated has been increasing. However, to accelerate ions, an accelerator system such as a synchrotron is required. Such systems are too large to install in general hospitals, and therefore, it is necessary to reduce the size of particle radiotherapy systems. One way to do this is to reduce the bending radius by increasing the magnetic field applied to the charged ions. Superconducting technology is suitable for this purpose, and LTS magnets designed to reduce the size of a rotating gantry, which is part of the irradiation equipment, have been developed in collaboration with NIRS [1]. To achieve further size reductions, high-T_c superconducting (HTS) magnets with higher magnetic fields are promising. And various research groups are working on development of HTS accelerator magnets [2]–[15].