China Southern Power Grid Corporation has started a project to study the feasibility of large-scale high-temperature superconducting (HTS) dynamic synchronous condensers (DSC) in Ultra High Voltage Direct Current (UHVDC) transmission grid. To investigate some key technologies, a small-scale prototype of HTS DSC of 300 kvar/2 poles/3000 RPM is under development. The electromagnetic design, especially the critical current of REBCO rotor coils was discussed. Besides, the configuration and properties of the air-core stator, the damper and the rotor were also described. Water-cooled windings in the air-core stator have a rated current density of 9.55 A/mm ² . Helium cooling pipes were embedded within REBCO rotor coils, and HTS windings will be cooled down to <; 30 K (<; 25 K for better) through conduction cooling. Two REBCO coil assemblies were manufactured and successfully tested in liquid nitrogen for several thermal cycles, which validated the manufacture techniques.

The High Intensity Heavy-ion Accelerator Facility (HIAF) is a new project under construction in China, which will provide beams of stable and unstable heavy ions with high energies, high intensities, and high quality. This paper discusses the superconducting magnet system for this accelerator complex. It will consist of a Nb ₃ Sn magnet with the peak field of 12 Tesla for the ECR ion source operated at 45 GHz, 52 solenoids typically 676 mm long with an operating field of 7.5 Tesla for the superconducting Linac called iLinac, 11 superferric dipoles with 320 mm wide good field region, 13 coil-dominated multiplets with an aperture of 320 mm, gradient 13 T/m for the fragment separator HFRS. This paper reports the design and prototype development status of the main components.

The Institute of Modern Physics (IMP) in Lanzhou, China, is currently developing a complicated superconducting magnet system composed of four solenoids and six sextupole coils based on a sextupole-in-solenoid configuration. The magnet is made of a single Nb3Sn wire and designed for a fourth-generation ECR ion source operating at frequency of 45 GHz. To effectively prevent the wires motion from performance degradations and a quench, a pre-stress is essential for the superconducting magnet winding and strengthening. Focusing on the sextupole magnet's assembly and the pre-load procedure, a combined support structure with temporary bladders, load pads, and load keys, as well an aluminum shell was designed and fabricated in this work. A whole assembly process was fulfilled with a dummy structure at room temperature and a cooling-down and warming-up cycle to show its validity. Some low-temperature resistance strain gauges, together with a half-bridge compensation, were used to monitor strain of the aluminum shell during the pre-load control performance and thermal cycle process. A parametric study on the equivalent friction of the combined structure was carried out for the mechanical characteristics based on FEM simulation to show a reasonable agreement with the experiment measurements as a proper friction coefficient chosen. Finally, a real sextupole magnet was assembled with the combined support structure and tested for excitation. It was illustrated that a proper pre-load state realized by the support structure and a high excitation current about 800 A was reached so that the excited magnetic field gained 7 T as the designed value.

The superferric superconducting dipoles are designed for the High energy FRagment Separator (HFRS) of the Heavy-ion Accelerator Facility (HIAF) in China. The dipole magnets of the separator will have a deflection radius of 15.7 m, a field up to 1.6 T with a ±160 mm × ±62 mm good field region and an effective length of 2.74 meters. In the HIAF-HFRS, there will be a total of 11 superferric dipoles under construction. The dipole consists of two superconducting coils, a coil casing, a cryostat, and a warm iron yoke. The superconducting coils are protected by the scheme of quench detection and energy-extraction. At present, the first prototype dipole has been fabricated and tested, which reaches the design current of 210 A without a quench and the magnetic field of 1.64 T at the good field area, meeting the physical requirements. The measured results of magnetic field and energy discharge behaviors are in good agreement with the calculations. This paper describes the details of mechanical design, construction and the testing results of the prototype.

A novel design for providing a high field based on a semi-open split Nb-Ti superconducting magnet has been developed. It is to incorporate in the versatile multi-field test facility established for professional tests of field-dependent and mechanical behaviors of low-temperature and high-temperature superconducting wires and tapes. The semi-open split superconducting magnet (the peak magnetic field in the coil up to 7.8 T) is a good candidate to generate a transverse field in a large work region of Ø100 mm × H800 mm. On the other hand, its semi-open shaped configuration for samples makes it feasible for a non-contact optical technology of digital image correlation (DIC) for being utilized in full-field deformation measurements under extreme conditions. Since the irregular-shaped configuration and large deformation due to attraction; mechanical behavior of support structures of the magnet will be crucial for its stability and operation function. In this study, an internal reinforced cantilever structure for splitting the superconducting magnet poles was proposed to bear the large attraction from Lorentz forces and keep a stable configuration under operation conditions. Analysis based on a finite element method was performed to obtain deformation and stress profiles of the superconducting coil windings and reinforced cantilever structure with contact nonlinearity. The effect of geometrical parameters of the cantilever on axial displacements in the split magnet system was addressed. Experiments on excitation and quench of the assembled split superconducting magnet were performed at 4.2 K to capture strain responses. The numerical predictions showed reasonable agreements with the observations on structural stress/strain states. It indicated that an optimization analysis of the cantilever structure is necessary for a high-field irregular-shaped magnet system for its assembly and excitation.

A conduction-cooled superconducting magnet producing a transverse field of 4 T has been designed for a new generation multi-field coupling measurement system, which will be used to study the mechanical behavior of superconducting samples at cryogenic temperatures and intense magnetic fields. A compact cryostat with a two-stage GM cryocooler is designed and manufactured for the superconducting magnet. The magnet is composed of a pair of flat racetrack coils wound by NbTi/Cu superconducting composite wires, a copper and stainless steel combinational former and two Bi₂Sr₂CaCu₂O_y superconducting current leads. The two coils are connected in series and can be powered with a single power supply. In order to support the high stress and attain uniform thermal distribution in the superconducting magnet, a detailed finite element (FE) analysis has been performed. The results indicate that in the operating status the designed magnet system can sufficiently bear the electromagnetic forces and has a uniform temperature distribution.