Development of a Fast-Ramping Dipole With Multi-Layer cos θ Configuration

Fast-ramping superconducting magnets are crucial for the next-generation high-intensity heavy-ion accelerators and cancer therapy machines. A fast-ramping superconducting dipole magnet featuring a multi-layer coil structure has been developed at the Institute of Modern Physics (IMP), Chinese Academy of Sciences. This magnet utilizes a modified cos θ configuration with rope-based cables. It consists of an 8-layer coil wound with two types of rope cables to improve conductor utilization efficiency. The coil layout was optimized through a linear programming algorithm. To reduce AC losses during fast-ramping operations, low-loss NbTi strands with CuMn matrix were employed, along with G10 formers. The magnet was optimized by integrating liquid helium channels and interlayer copper strips to enhanced heat conduction, based on AC loss estimates and thermal simulations. A shell-based structure utilizing bladder and key technology was employed to pre-stress the superconducting coils. An 800 mm-long dipole prototype was manufactured, assembled, and tested in liquid helium. After 76 quenches, the dipole prototype achieved a central magnetic field of 6 T and a maximum ramp rate of 1.01 T/s. This paper presents the design, fabrication, assembly, and test results of the prototype dipole magnet.