Screening Currents and Hysteresis Losses in the REBCO Insert of the 32 T All-Superconducting Magnet Using <i>T-A</i> Homogenous Model

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: 89%

Screening-current-induced mechanical strains in REBCO insert coils

Yan

Song

Xin

et al. 2021

“…B n denotes the normal component of the magnetic field B. The current density J determines the electric field E. And the E-J relationship for the REBCO conductor is expressed as [34,35]…”

Section: D Electromagnetic Model Based On T-a Formulationmentioning

confidence: 99%

“…] b (7) where B par and B per denote the magnetic field components parallel and perpendicular to the tape surface, respectively, J c0 is the critical current density. k, b, and B c are shape parameters describing the anisotropic characteristics of the REBCO conductor, and k = 0.009 13, b = 0.7518, and B c = 467.4 mT [34]. Equation ( 8) is used to calculate the normalized critical current of the ReBCO layer.…”

Section: D Electromagnetic Model Based On T-a Formulationmentioning

confidence: 99%

Investigating the effect of transverse compressive loads on the electromagnetic performance of superconducting CORC^® cables

Yan¹,

Wang²,

Gao³

et al. 2022

High-temperature superconductor (Re)Ba2Cu3Ox (ReBCO) conductor on round core cable (CORC®) has a large current carrying capacity for high field magnets. Lorentz forces acting on CORC conductors, cause a reduction of the critical current, or even permanent degradation of their performance when exceeding critical values. Transverse compressive stress is one of the principal mechanical stresses when CORC cables are bundled to CICC conductors capable of operating at currents up to 100 kA in magnetic fields of up to 20 T. In this research, a mechanical-electromagnetic model is developed to study the effect of transverse compressive loads on the electromagnetic performance of CORC cables. A mechanical transverse load on the cable is implemented to simulate the electromagnetic force. A comparison of numerical simulations with experiments for a three-layer CORC cable is first performed to validate the model's reliability, with particular attention to critical current reduction during the transverse compression process. A novel feature of this paper is that the model developed can analyze both mechanical response under transverse compressive loads and electromagnetic performance under applied AC magnetic fields with low amplitudes. On this basis, the model investigates the effects of winding parameters on the axial strain and critical current reduction of the ReBCO layer in a single-layer CORC cable. The numerical analysis shows that increasing the winding angle can reduce the axial strain and critical current reduction of the ReBCO layer in the contact area. Subsequently, a detailed comparative study is carried out studying the axial strain of the ReBCO layer in the non-contact area with and without taking the winding core into account. In addition, a sudden increase of the magnetization loss is explained when the transverse compressive load reaches a certain level. Finally, a six-layer CORC cable's electromagnetic analysis is performed, and each tape layer's critical current reduction is investigated and discussed. The comparison of magnetization loss and current density between six- and single-layer CORC cables in the no-strain case is also given. This FE model can guide optimizing a cable design for specific application conditions.

“…Xia et al [81] simulated the mechanical responses and superconducting screening currents in a REBCO high-field coil with a stack of pancakes and a large number of turns in relation to the 32 T magnet developed at NHMFL [82,86]. The 32 T NHMFL magnet comprises a 15 T (250 mm bore) outer LTS coil set (NbTi and Nb 3 Sn) with a 17 T (32 mm cold bore) dry-wound NI REBCO insert, with an original designstress of 400 MPa and 440 MPa on the inner and outer REBCO pancake coils, respectively [24].…”

Section: Modeling Of Screening Currents and Associated Unevenmentioning

confidence: 99%

Topical Review: Multifilamentary coated conductors for ultra-high magnetic field applications

Wulff

Abrahamsen

Insinga

2021

High-temperature superconducting coated conductors (CCs) are considered an enabling ultra-high field (UHF) tape-conductor technology due to their extremely high engineering current densities at very high magnetic fields and low temperatures, and high mechanical strength. A major challenge is however related to induction of problematically large superconducting screening currents (as an effect of the large width-to-thickness ratio) when the wide tape conductors are exposed to strong transverse magnetic fields above 20 T, which is the case in many UHF magnet systems. Subdividing the superconducting layer into narrow parallel decoupled filaments has been shown to effectively reduce superconducting screening currents by a factor comparable to the number of filaments. The filamentization is however not effective until the induced coupling currents flowing across the filaments have decayed. The effectiveness of the multifilamentary structure in suppressing coupling currents and reducing the decay time constants is directly linked to potential current paths between filaments. Very recent experimental and numerical studies have examined both the challenge of magnet precision, caused by screening-current-induced fields, and the fatal consequences of local uneven tape stresses exceeding the irreversible limits for commercial CCs. These studies have conclusively revealed that screening currents must not be ignored in the mechanical design and other studies have introduced multifilamentary CCs as a viable solution. This paper aims to review the efforts made in developing and investigating multifilamentary CCs for ultra-high field applications focusing on the screening-current-related mechanisms, critical system-level effects, effectiveness of filamentization in UHFs, fabrication and large-scale analysis of multifilamentary CCs, in addition to providing cost estimates of previously studied filamentized CC fabrication techniques.