Construction and Test of a 7 T Metal-as-Insulation HTS Insert Under a 20 T High Background Magnetic Field at 4.2 K

The double-layer metal-insulation method using the brass sheets as the double-layer insulators was proposed in this paper. It can enhance the contact resistivity while reserving greater thermal conductivity merit. The underlying mechanism of the contact resistivity enhancement is to increase the number of contact surfaces and to degrade the contact quality between the insulators. Then, we wound a single-layer brass-insulation coil and a double-layer brass-insulation coil to compare their contact resistivities and confirmed the effectiveness of the double-layer metal-insulation method. Besides, since the capacity withstanding the overcurrent is weakened with the increscent contact resistance of the metal-insulation coil, we further investigated the influence of the contact surface resistivity distribution on the coil performance under different scenarios to optimize the double-layer metal-insulation coil for receiving a superior thermal stability. Simulation results indicated that the coil possessed the dominated 2nd contact surface resistivity and minimum 1st and 3rd contact resistivity is the optimal design for the double-layer metal-insulation coil to receive the best thermal stability, irrespective of the cooling environment, contact resistivity magnitude, operating current and coil dimension. In addition, in regard to the thermal performance differences caused by the contact surface resistivity distribution, we found that the increment of contact surface resistivity and the overcurrent would enlarge the distinctions at different levels.

Section: Introductionmentioning

confidence: 99%

Performance enhancement of coated conductor magnet with double-layer metal insulation

Wang

Zhou

et al. 2023

“…Owing to this self-protecting nature, the NI technique has attracted considerable attention from superconducting magnet designers and many NI magnet projects have been accomplished [1][2][3][4][5][6][7] or in progress [8,9]. Other variants of no-insulation magnets including 'metal as insulation (MI)' [10,11] and 'intra-layer noinsulation (LNI)' [12,13] have also been constructed. A noinsulation magnet is under development for the application of high-frequency gyrotron at Wuhan National High Magnetic Field Center, China.…”

Section: Introductionmentioning

confidence: 99%

Quench analysis of a no-insulation REBCO magnet based on the ADI method considering the coupling effect of the cryostat

Zheng,

Liu,

Song

et al. 2023

A no-insulation (NI) REBCO superconducting magnet is under development at Wuhan National High Magnetic Field Center, China. The magnet with the liquid helium cryostat system has a compact structure to reduce the space required for operation. During a quench, the fast-changing spatial magnetic field around the NI magnet may induce a strong eddy current in the conductive parts of the cryostat. The eddy current and its associated Lorentz force will generate mechanical stress on the cryostat, especially on the thermal shield (TS). The mechanical strength of the cryostat needs verification in the preliminary design. Furthermore, the degree to which the electromagnetic coupling between the cryostat and NI magnet might impact the quench behaviors of the NI magnet remains uncertain. In this paper, a multi-physics quench model is newly developed for the NI REBCO magnet, and the alternating direction implicit method is employed for the solver of the thermal model to improve computational efficiency. This simulation model can consider the electromagnetic coupling effect between the NI magnet and cryostat by constructing a partial element equivalent circuit. A quench analysis has been performed and we found that: (1) The cryostat can function as a secondary shorted circuit to the NI magnet and slow down the quench speed to a certain extent. (2) During the rather fast inductive quench phase, the cryostat will experience an attraction force towards the quench propagation frontier. (3) A quench propagation from one end of the magnet can cause a significant z-axis unbalanced force on the TS. (4) Cryostat materials with drastically changed electrical conductivity can significantly affect their mechanical responses during a quench. However, the eddy current density and maximum Von Mises stress on the TS are barely affected by the thickness of the TS and the contact resistance of the NI REBCO magnet.

“…motors, generators, nuclear magnetic resonance (NMR), and magnetic resonance imaging [1][2][3][4]. Due to their superior currentcarrying capacity under high fields and high mechanical strength, CCs are recognized as promising materials in the pursuit of ultra-high-field magnets [5][6][7][8][9][10]. To date, several highfield magnets have been built by adopting REBCO coils as their essential components [1, 5-7, 11, 12], such as the 18.8 T REBCO insert for the NMR magnet at the Francis Bitter Magnet Laboratory [1], the 32 T all-superconducting magnet in the National High Magnetic Field Laboratory (NHMFL) [5], the 32.35 T all-superconducting magnet constructed using the noinsulation (NI) technique at the Institute of Electrical Engineering, Chinese Academy of Sciences [6], and very recently, a stronger 45.5 T magnet with 14.4 T NI REBCO coils as its inserts [7].…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of the electromechanical behavior of high-field REBCO coils in all-superconducting magnets

Niu

Xia

Yong

2021

Despite the excellent improvements in high fields resulting from the adoption of REBa2Cu3O x (REBCO)-coated conductors (CCs), the resulting stress and strain due to winding tension, cooling stress, and the screening-current-induced Lorentz force may lead to severe plastic deformation and degradation of superconductivity. Therefore, it is essential to understand the comprehensive electromechanical behavior and deformation mechanism of high-field REBCO magnets. In this paper, multistep finite element analysis is designed to simulate the electromechanical behavior of REBCO coils after the winding, coolingdown, and charging processes. All major constituent materials including the mandrel, CCs, cowinding reinforcement, and over-banding are considered in the mechanical models to emulate contact–separation behavior between them. In addition to contact nonlinearity, an intrinsic elastoplastic property is introduced to predict the plastic deformation observed in experiments. To reveal the screening-current effect, the distributions of the screening current and the magnetic field are analyzed by solving the T-A formulation of Maxwell’s equations using a homogeneous technique. Then, with the electromagnetic load acting as a body force, the electromagnetic stress and strain are computed and experimentally validated for a pancake coil, including the transport current and external field. Finally, the electromechanical behavior under a Lorentz load is investigated by considering the accumulation of stress and strain due to winding tension and cooling down. The simulation results reveal that the winding tension and thermal stress affect the final stressstates in the fully charged state and therefore the electromechanical properties. Both plastic deformation and possible degradation are more likely to occur in the outermost tape of several pancakes due to the influence of screening-current-induced stress and strain. In addition, this work further analyzes the effect of the current sweep reversal method, which could be favorable in reducing the screening-current-induced high stress and strain in the steady state.