A novel REBCO conductor design to reduce screening-current field in REBCO magnets

Self Cite

In recent years, remarkable progresses have been made in the R&D efforts for high temperature superconducting (HTS) high-field magnets. The screening-current-induced magnetic field and mechanical stress/strain in rare-earth barium-copper-oxide (REBCO) coils are raising growing concerns. This paper presents experimental and theoretical analyses on the effects of screening-current-induced mechanical strains in a REBCO insert setup without transport currents. Strain measurements on two REBCO coils, with and without over-banding structures, were carried out in an low temperature superconducting (LTS) background field magnet. Electromagnetic-mechanical models were developed, coupling the tilting angles of the superconducting tapes and the strain dependency of the critical current. The discrete-coupled model with turn-to-turn contacts, the discrete-sequential model and the block model were implemented and compared against the measured hoop strains. Combining experimental data with simulation models, it is shown that moderate over-banding structures are effective in providing reinforcements for the superconductors. A new method of edge-bonding was proposed and tested, which could reduce hoop strains in low applied fields but failed in higher fields. This work could be useful for the design and analysis of future high-field REBCO magnets.

Section: Introductionmentioning

confidence: 99%

Screening-current-induced mechanical strains in REBCO insert coils

Yan

Song

Xin

et al. 2021

Self Cite

“…The usage of coated conductors divided into totally decoupled 0.6 mm-0.9 mm wide filaments could reduce the SCF of REBCO coils to a comparable level as their Bi-2223 counterparts (figure 2). Wang et al developed a 1mm wide Narrow-Stacked (NS) REBCO tape [57,60]. Experiments on coils wound with this type of conductors reported a similar effect on the SCF.…”

Section: Geometrical Configurationsmentioning

confidence: 99%

Screening current induced magnetic field and stress in ultra-high-field magnets using REBCO coated conductors

Yan

2021

Self Cite

Rare-earth-based barium copper oxide (REBCO) coated conductors are promising candidates for the development of ultra-high-field (UHF) magnets, due to its high in-field performance, engineering current density, tensile strength and commercial availability. However, technological challenges pertaining to the large screening currents still remain. The major issues caused by the screening currents in REBCO conductors in UHF applications involve two aspects: the screening current induced magnetic field (SCF), and the screening current induced stress (SCS). In the past decades, extensive research has been devoted to the SCF, offering a variety of possible remedies. With latest advances in the construction and testing of UHF magnets, new observations of the SCF involving REBCO coils were reported. The SCS was identified in recent years and has raised growing concerns. The excessive and highly concentrated Lorentz force, rooted in the high magnetic field and the screening currents, poses threats to the mechanical strength of REBCO coated conductors. The aim of this paper is to review recent research efforts in understanding and tackling the screening current related technological issues. For the SCF, we focus on the latest observations in high-field experiments and its various mitigation methods. For the SCS, we present recent studies including experimental characterizations, numerical modelling and possible countermeasures. It is still an open question to precisely predict the SCS in large-scale HTS magnets. How to minimize the influence of SCF and SCS is one of the key technical challenges for the design of future UHF magnets.

“…The issue of distorted magnetic fields produced by an induced persistent screening current in the tape under timevarying conditions was studied in [41]. A novel REBCO conductor design, consisting of narrow-stacked (NS) wire, bundling 1 mm wide tapes was used for this study.…”

Section: High Field Magnetsmentioning

confidence: 99%

The T-A formulation: an efficient approach to model the macroscopic electromagnetic behaviour of HTS coated conductor applications

Huber

Song

Zhang

et al. 2022

Self Cite

In recent years, the T-A formulation has emerged as an efficient approach for modelling the electromagnetic behaviour of high-temperature superconductor (HTS) tapes in the form of coated conductors (CCs). HTS CCs are characterized by an extremely large width-to-thickness ratio of the superconducting layer, normally up to 1000~6000, which in general leads to a very large number of degrees of freedom. The T-A formulation considers the superconducting layer as infinitely thin. The magnetic vector potential A is used to calculate the magnetic field distribution in all simulated domains. The current vector potential T is used to calculate the current density in the superconducting layer, which is a material simulated with a highly nonlinear power-law resistivity. This article presents a review of the T-A formulation. First, the governing equations are described in detail for different cases (2D and 3D, cartesian and cylindrical coordinates). Then, the literature on the implementation of T-A formulation for simulating applications ranging from simple tape assemblies to high field magnets is reviewed. Advantages and disadvantages of this approach are also discussed.