Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling

Takahashi, Shunji; Suetomi, Yu; Takao, T.; Yanagisawa, Yoshinori; Maeda, Hideaki; Takeda, Yasuhisa; Shimoyama, Jun–ichi

doi:10.1109/tasc.2020.2974837

Cited by 71 publications

(56 citation statements)

References 21 publications

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“…The explanation offered is the plausible one that the inner edge compression is plastically unstable. In our case, the much larger tensile stresses in the outer edges may stabilize the inner edges since the maximum tensile stresses in the RIKEN test coil were <400 MPa even with significant screening current amplification (∼4) [23].…”

Section: Local Damage Due To Pre-existing Micro Cracks and Their Prop...mentioning

confidence: 63%

“…Thus, the outer edges experience a hoop stress expansion and the inner edges a compression. We did indeed look for damage at the inner edges but did not find it but buckling of this edge in test coils operating at lower stresses and lower fields has recently been reported [23]. The explanation offered is the plausible one that the inner edge compression is plastically unstable.…”

Section: Local Damage Due To Pre-existing Micro Cracks and Their Prop...mentioning

confidence: 77%

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Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

Small

Kim

et al. 2020

Supercond. Sci. Technol.

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REBCO coated conductors are now being used for building very high-field magnets with large electromagnetic stresses, both expected ones due to transport current ⃗ J × ⃗ B stresses and additional stresses resulting from the large screening currents inherent in wide tapes. Post mortem analyses of several recent test coils operated above 40 T show that significant conductor plastic deformation occurs, even for JBR stresses well below the ∼1 GPa yield of the Hastelloy substrate of the conductor. To investigate these deformation mechanisms, conductors were unwound after coil test and carefully examined with respect to their length-wise I c which revealed many areas of local damage. Regions of interest were examined by metallographic cross-section, Hall microscopy, magneto-optic imaging and scanning electronic microscopy. Important damage frequently occurred to the outer edges of pancakes in the coil ends, which were often plastically deformed over the whole turn circumference, especially when this outer edge was a slit edge. Internal conductor damage was also seen, especially delamination between the buffer and REBCO layers at slit edges. Careful sectioning of the tape at ∼10 mm intervals showed that the plastic deformation of the turns was complex and variable around the turn circumference, with tape cross-sections that exhibited continuous shape change in the outer turns. The bending center line of tapes often shifted from the tape center line toward the edge closest to the coil center, indicating asymmetric effects of transport and screening current stresses across the conductor width. A surprising and vital result is that damage was prevalent when the slit edge was also the edge at which transport current flowed. This damage was absent when the transport current flowed at the not-slit edge, implying great sensitivity of the effect of screening current stresses to localized conductor damage.

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Section: Local Damage Due To Pre-existing Micro Cracks and Their Prop...mentioning

confidence: 63%

Section: Local Damage Due To Pre-existing Micro Cracks and Their Prop...mentioning

confidence: 77%

Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

Small

Kim

et al. 2020

Supercond. Sci. Technol.

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“…Meanwhile, the screening current (SC) induced in the REBCO CCs generates an undesired magnetic field [12,13,14,15]. Recently, it was pointed out that the screening current may substantially enhance magnetic stress in REBCO magnets [16,17,18,19,20,21]. To estimate the peak stress accurately, the importance of the accurate computation of the screening current distribution must be enhanced.…”

Section: Introductionmentioning

confidence: 99%

A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model

Noguchi¹,

Hahn²

2022

Supercond. Sci. Technol.

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Since the screening current (SC) in rare earth-barium-copper-oxide (REBCO) coated conductor (CC) generates an undesired magnetic ﬁeld, it must be accurately estimated, especially for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). Moreover, in recent years, it was pointed out that the screening current enhanced the stress/strain in REBCO CC, when an REBCO magnet was operated as an insert under an ultrahigh magnetic ﬁeld. The previously reported SC simulation methods may be roughly categorized into ﬁnite element method (FEM) and equivalent circuit method. The FEM-based method often adopted an axisymmetric model or a thin ﬁlm approximation model, while the circuit-based are the simple equivalent circuit model and the network equivalent circuit model, so-called the partial element equivalent circuit model. The latter is newly proposed in this paper. Features of those SC simulation models are brieﬂy compared to each other in this paper. Each SC simulation models have pros & cons. We have to adequately chose an SC simulation model depending on a purpose. In addition, we propose a new developed SC simulation model, named the advanced partial element equivalent circuit (A-PEEC) model. It is extendable to an SC simulation of no-insulation REBCO pancake coils. To simulate the SC of a simple coil model and the LBC3 magnet, we investigated the screening current distribution maps, and the simulated screening current-induced ﬁelds were compared with the measurements. We have conﬁrmed the validity of the newly proposed A-PEEC model.

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“…So far, some journal papers on mechanical simulation on REBCO magnets have been published [11]- [14]. In these papers, the finite element method (FEM) was employed as a mechanical simulation.…”

Section: Introductionmentioning

confidence: 99%

Plastic Deformation Simulation of REBCO Tapes Using Particle Methods

Mato

Noguchi

2022

IEEE Trans. Appl. Supercond.

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Ultra-high field superconducting magnets are facing a mechanical degradation problem. On 2017, a world-record high DC magnetic field of 45.5 T was generated by insert no-insulation (NI) Rare-Earth Barium Copper Oxide (REBCO) pancake coils (14.4 T), called "LBC3", and an outsert resistive magnet (31.1 T). Although the experiment showed a high potential of the NI REBCO magnets for ultra-high field generation, the insert NI REBCO pancake coils and the REBCO tapes were plastically deformed. The critical current properties of damaged REBCO tapes were degraded although the Hastelloy substrate of REBCO tapes is stiff and it has a high yield point of approximately 1 GPa. However, the mechanisms of the damaging REBCO tapes are not clarified. Therefore, it is necessary to clarify the mechanical phenomenon of REBCO tapes.In this paper, we model a REBCO tape with a smoothed particle hydrodynamics (SPH) method, which can represent plastic deformation. The SPH simulation is coupled with electromagnetic analysis with a partial element equivalent circuit (PEEC) model which we have previously developed. In the simulation, an external field, which linearly increases to 5 T and then decreases to 0 T, is applied to a short-length REBCO tape. The simulation results show that the REBCO tape largely deforms during the external field excitation and deexcitation.

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Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling

Cited by 71 publications

References 21 publications

Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

Analyses of the plastic deformation of coated conductors deconstructed from ultra-high field test coils

A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model

Plastic Deformation Simulation of REBCO Tapes Using Particle Methods

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