Jefferson Lab and General Atomics are jointly advancing compact, high-power irradiation systems capable of delivering electron-beam powers in the hundreds of kilowatts based on superconducting radio-frequency (SRF) technology. A critical step toward deploying SRF accelerators in industrial environments is replacing traditional liquid-helium cryogenic systems with conduction-cooled cryomodules powered by commercial cryocoolers. This paper reports recent progress in the design, fabrication, and testing of a prototype three-cell SRF cavity developed at Jefferson Lab and evaluated in a dedicated horizontal test cryostat at General Atomics. Peak surface magnetic fields up to 18.4mT, corresponding to accelerating gradients of approximately 4.3MV/m, were achieved in one of the cells. The results provide key insights into cavity preparation, thin film coating, mechanical robustness, and cryogenic integration, offering guidance for the continued maturation of compact, conduction-cooled SRF accelerators for industrial irradiation applications.
The REBa2Cu3O7-δ (REBCO, where RE represents rare earth elements such as Y, Gd, Nd, Sm, etc.) ring-shaped bulk superconductors hold significant potential for high-field and magnetic shielding applications. This study systematically investigates how the geometric dimensions (including outer radius (R), inner radius (r), radial thickness (R-r), and vertical thickness (H)) influence the trapped magnetic field (Btr) in single domain REBCO ring-shaped bulk superconductors. The main focus of this research has been centered on the strength and distribution of the Btr profile. And the key findings are as follows: (1) The maximum value of the Btr increases with increasing outer radius; (2) Increasing the inner radius leads to a reduced the peak field but enhances uniformity in the central cavity; (3) The maximum value of Btr increases with vertical thickness in a nonlinear manner before reaching saturation. The saturation vertical thickness depends strongly on radial thickness and ceases to increase once the radial thickness reaches approximately 0.8R. (4) When 0 < r ≤ 0.2R, the ratio of the saturated vertical thickness to the diameter (2R) for the ring-shaped bulk is approximately 1.3. These results provide critical insights for topology optimization in compact magnets, magnetic shielding, and nuclear magnetic resonance applications.
The poloidal-field (PF) coil system for the EU DEMO 2024 low-aspect-ratio (LAR) baseline is preliminarily designed using a common Nb-Ti rectangular cable in a stainless steel jacket, wound as multiple double pancakes. Compared with earlier DEMO baselines, the updated LAR field distribution allows all six PF coils (PF1–PF6) to be realized with Nb-Ti, avoiding Nb3Sn in the present design space. Coil currents are derived from scenario-dependent ampere-turn requirements, and conductor cross-sections are sized iteratively from the peak magnetic field using an integrated MATLAB–COMSOL workflow. The procedure combines a Nb-Ti Jc(B) law with explicit limits on superconducting and copper current density, cable current, geometric envelope, and jacket mechanical fatigue. The converged design yields peak fields of 3.64–5.54 T, jacket thicknesses of 5–11 mm, and hydraulic lengths of 849–1951 m. All coils satisfy the adopted current-density and jacket-fatigue criteria; PF1 and PF4 exceed their radial and vertical envelopes by approximately 31 and 10 mm, respectively, requiring minor integration adjustments. A 2D axisymmetric structural screening indicates a maximum von Mises stress of 311 MPa, suggesting that the static stress state is not dimensioning; jacket sizing is instead governed by the separate fatigue-screening criterion. The resulting dataset provides a consistent basis for subsequent cooling, integration, and full 3D support-structure assessments.
A 16.5 T NbTi-Nb3Sn superconducting magnet with a 150 mm bore has been successfully developed at the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). The magnet is designed as a general-purpose background field magnet and is composed of four concentric coaxial solenoid coils, including three Nb3Sn coils and one NbTi coil. To achieve optimized current density distribution, the Nb3Sn coils were wound using multiple Nb3Sn conductors with different performance characteristics, enabling effective classification and optimization of operating current density. Comprehensive stress and strain simulations were conducted to evaluate the mechanical behavior of the magnet. In addition, a passive quench protection system was specifically designed to ensure reliable protection of the magnet during quench events. Quench simulations confirmed that the passive protection circuit effectively limits coil voltage, mechanical stress, and temperature rise to safe levels. Experimental results demonstrate that the magnet successfully generated a central magnetic field of 16.5 T at 4.2 K under liquid helium immersion, validating the overall design and performance. This paper provides a detailed description of the electromagnetic design, stress and strain analysis, quench protection strategy, as well as the fabrication and experimental testing of the magnet.
