Thermal characteristics of a helium-free superconducting magnet system for a fast-ramping heavy-ion synchrotron. (September 2022)

• Record Type: Journal Article
• Authors: Yang, Ye; Mizushima, Kota; Matsuba, Shunya; Fujimoto, Tetsuya; Noda, Etsuo; Urata, Masami; Shirai, Toshiyuki; Takayama, Shigeki; Amano, Saki; Orikasa, Tomofumi
• Is Part Of: Cryogenics. Volume 126(2022)
• Publication Date: 2022-09
• Subjects: Superconducting magnet -- Heavy-ion therapy -- Conduction-cooling -- Cryocooler -- AC loss -- Magnetization -- Eddy current -- Iron loss -- Dynamic simulation; 0000 -- 1111; Low temperature engineering -- Periodicals; Low temperature research -- Periodicals; 536.56
• DOI: 10.1016/j.cryogenics.2022.103524
• Languages: English
• ISSNs: 0011-2275

Abstract

Highlights: Feasibility for realizing a helium-free superconducting magnet operated at a ramp rate of 0.7 T/s was investigated. Models for the calculations of the iron loss, hysteresis loss and eddy current loss were presented. Temperature rise during the operation was estimated by a dynamic simulation. Design of a helium-free superconducting magnet system was established. Abstract: A compact synchrotron has been proposed for the next generation heavy-ion therapy system at the National Institutes for Quantum Science and Technology (QST). In this synchrotron, four 90-degree superconducting bending magnets designed on the basis of the superconducting magnet for the rotating-gantry currently operated at QST are adopted to achieve a compact size. These NbTi superconducting bending magnets are conduction-cooled by several Gifford–McMahon (GM) cryocoolers and are designed to generate both the dipole field of 3.5 T and the quadrupole field of 1.5 T/m to operate at a ramp rate of 0.7 T/s. It is a challenge to remove the heat generated from AC losses at such a fast ramp rate, and keep the superconducting magnets from quenching during the continuous operation without using liquid helium. In this paper, we studied the feasibility for realizing a fast-ramping synchrotron by using a helium-free superconducting magnet system for heavy-ion therapy. Using the numerical models, we estimated the AC losses including eddy current loss in mechanical structures, iron loss and loss in superconductor to be about 212 J in a cycle duration of 20 s for each 90-degree superconducting bending magnet, and it was possible to eliminate that amount of AC losses by using GM cryocoolers. To validate the transient temperature rising during the continuous operation, a dynamic simulation was performed using the estimated AC losses as input, and the peak temperature at thermal equilibrium was evaluated to be lower than 5 K for a practical operation scenario of heavy-ion therapy irradiation.