Screening-Current-Induced Strain Gradient on REBCO Conductor: An Experimental and Analytical Study With Small Coils Wound With Monofilament and Striated Multifilament REBCO Tapes

Li, Yi; Park, Dong Keun; Lee, Woo Seung; Choi, Yoon Hyuck; Tanaka, Hiromi; Bascuñán, J.; Iwasa, Y.

doi:10.1109/tasc.2020.2974857

Cited by 43 publications

(46 citation statements)

References 29 publications

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“…The so-called 'index' model with n = 21 was adopted to model the non-linear E-J characteristics of the REBCO tapes and domain homogenization and the 2D edge element formulation were adopted so as to be able to simulate both transport and screening currents simultaneously [24]. Recently several groups have reported similar simulations of screening current stress for various REBCO coils [23,[25][26][27]. A common feature is that none is yet numerically perfect.…”

Section: The Beneficial Effects Of Incorporating Screening Current St...mentioning

confidence: 99%

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: The Beneficial Effects Of Incorporating Screening Current St...mentioning

confidence: 99%

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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“…Plastic deformation was observed on the HTS tapes during post mortem analyses of the LBCs [6,18]. Subsequently, the effect of SCIS was demonstrated quantitatively on small coils by direct measurements of the in-field hoop strains [19][20][21]. Theoretical models taking into account the turn-to-turn contacts in the dry-wound structure and the distribution of the screening currents were developed and applied to large-scale magnets [22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

“…However, contrary to experimental observations, sequential models of the in-field insert magnet often predict extremely high hoop strains exceeding the critical strains [22,23,27]. Overestimation of the SCIS using direct simulations was also found in measured hoop strains in [19,20]. The simulated hysteresis loop in the 32 T all-superconducting magnet using a electromagnetic model was much wider than the measured one [11,28].…”

Section: Introductionmentioning

confidence: 99%

“…The simulated hysteresis loop in the 32 T all-superconducting magnet using a electromagnetic model was much wider than the measured one [11,28]. It was suggested by Li et al [20] that tilting of the superconducting tape could affect the magnetization process, particularly with a high axial-field to radial-field ratio. A report on the SCIF in the 32 T high-field magnet by NHMFL [29] suggests that the discrepancy between simulations and measurements could be reduced by incorporating the tilting angles in the electromagnetic model.…”

Section: Introductionmentioning

confidence: 99%

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Screening-current-induced mechanical strains in REBCO insert coils

Yan

Song

Xin

et al. 2021

Supercond. Sci. Technol.

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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.

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“…Hahn et al observed widespread post-quench mechanical damage, including an irreversible wavy deformation, on the edges of the REBCO conductors [14], advocating that the conductors were overstressed due to the SC-associated Lorentz force [26]. This SCassociated stress modification was then explained by numerical simulations [24,27] and studied in detail with small-scale experiments [28][29][30].…”

mentioning

confidence: 99%

Analyzing full electromagnetic behaviors of no-insulation, high-temperature superconducting coils with turn-to-turn bypass currents and persistent screening currents

2020

Supercond. Sci. Technol.

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Screening-Current-Induced Strain Gradient on REBCO Conductor: An Experimental and Analytical Study With Small Coils Wound With Monofilament and Striated Multifilament REBCO Tapes

Cited by 43 publications

References 29 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

Screening-current-induced mechanical strains in REBCO insert coils

Analyzing full electromagnetic behaviors of no-insulation, high-temperature superconducting coils with turn-to-turn bypass currents and persistent screening currents

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