Field Measurements of Prototype Superconducting Magnet for a Compact Heavy-Ion Therapy Synchrotron

A synchrotron using superconducting magnets has been designed for a next-generation heavy-ion therapy system at National Institutes for Quantum Science and Technology. The maximum central field and ramp rate of their magnets are 3.5 T and 0.7 T/s, respectively, and a field homogeneity of 10 ^–4 unit is required. To verify field generation and thermal characteristics, a prototype superconducting magnet was fabricated. This first prototype was designed as a short-straight model with a length of 400 mm and a cross section equal to that of a full-scale magnet. The magnet was conduction-cooled at cryogenic temperatures and energized up to a nominal current of 265 A. Its central field was then measured by hall sensors. Descriptions of the design and fabrication of the first prototype magnet and the results of the magnetic-field measurements are reported in this paper.