Study on elimination of screening-current-induced field in pancake-type non-insulated HTS coil

Kim, K L; Song, Jung-Bin; Yang, Dong; Kim, Y G; Kim, T H; Kim, S K; Park, M W; Lee, H G

doi:10.1088/0953-2048/29/3/035009

Cited by 15 publications

(8 citation statements)

References 30 publications

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“…There are some remedies for the SCIF and the field drift. For example, the SCIF can be reduced by applying an external AC magnetic field forcing the "vortex shaking effect" [24]. A method to reduce the field drift is by lowering the temperature once the operating current is reached, then the critical current is increased and the flux creep diminishes [2].…”

Section: Striation and Current Sweep Reversalmentioning

confidence: 99%

Screening Current-Induced Field and Field Drift Study in HTS coils using T-A homogenous model

Berrospe-Juarez

Trillaud

Zermeño³

et al. 2020

J. Phys.: Conf. Ser.

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The emergence of second generation (2G) high-temperature superconductor (HTS) tapes has favored the development of HTS magnets for their applications in areas such as NMR, MRI and high field magnets. The screening current-induced field and the field drift are two major problems hindering the use of HTS tapes in the mentioned areas. Both problems are caused by the screening current, then it is necessary to have a modeling strategy capable to estimate such phenomena. Thus far, the H formulation has been a widely used approach to model medium-size systems (hundreds of tapes). However, its application to large-scale systems is still impaired by excessive computation times and memory requirements. Homogenization and multi-scaling strategies have been successfully implemented to increase the computational efficiency. In this contribution, we show that using the homogenization technique with the recently developed T-A formulation allows reducing the computation time and the amount of memory up to the point that realtime simulations of slow ramping cycles of large-scale systems are possible. At the same time, the T-A homogeneous model provides enough resolution to investigate the screening current using numerical simulations.

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Section: Striation and Current Sweep Reversalmentioning

confidence: 99%

Screening Current-Induced Field and Field Drift Study in HTS coils using T-A homogenous model

Berrospe-Juarez

Trillaud

Zermeño³

et al. 2020

J. Phys.: Conf. Ser.

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“…SCFs, induced when an REBCO magnet is exposed to a timevarying magnetic field, is a major source of temporal field instability in the magnet [11][12][13][14][15][16][17][18][19][20][31][32][33][34]. Time-varying field distributions, resulting from SCFs, make it difficult to calculate accurate field gradients and implement proper arrays of ferromagnetic shims for REBCO magnets.…”

Section: Protocol To Mitigate Scfsmentioning

confidence: 99%

“…No-insulation REBCO magnets have in particular attracted interest because they remain undamaged subsequent to quenching as opposed to the insulated types, which are usually damaged [5][6][7][8][9][10]. REBCO conductors are only available in a tape form, and no-insulation REBCO magnets hence have very large screening currents all around the conductors [11][12][13][14][15][16][17][18][19][20][21]. Unfortunately, the screening currents become relaxed over the long term to cause a considerable drift of the magnetic field [22], and the currents are very difficult to predict and take into account while such magnets designed, a situation greatly detrimental to their field homogeneity as well [23].…”

Section: Introductionmentioning

confidence: 99%

“…While energizing a large-scale no-insulation REBCO magnet fabricated with stainless-steel clad REBCO tapes [24], the application of a specific ramping pattern to a target current mitigates the magnetic field induced by the screening currents significantly and accelerates the elimination of its long-term drift [22]. Nonetheless, it is challenging for noinsulation REBCO magnets to be manipulated to have NMRquality field homogeneity [20,22,[25][26][27][28], which corresponds to tiny field gradients. In particular, there have been few attempts with no-insulation REBCO magnets to verify if the mitigation of the screening-current-induced fields (SCFs) improves the spatial and temporal quality of the field homogeneity of such magnets up to a level for use in NMR.…”

Section: Introductionmentioning

confidence: 99%

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Reproducibility of the field homogeneity of a metal-clad no-insulation all-REBCO magnet with a multi-layer ferromagnetic shim

Jang

Hwang

Han

et al. 2020

Supercond. Sci. Technol.

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We report that the field homogeneity of a large-scale metal-clad no-insulation all-ReBa 2 Cu 3 O 7−x magnet is reproducible after occasional operating conditions, in this case the current ramp down/ up and magnet warm-up/cool-down conditions. First, we shimmed the magnet by cylindrically arraying ferromagnetic shims on the wall of the room-temperature bore of the magnet to improve the spatial field homogeneity. As a result, the field homogeneity of the magnet was improved from 557.7 to 14.1 ppm in a 10 mm diameter spherical volume. The resultant acquisition of field homogeneity tremendously enhanced from an inhomogeneous state greatly degraded by screening currents qualified us to study the temporal stability of the field homogeneity. We used a magnet-energizing protocol with the field drift minimized to shrink a nuclear magnetic resonance (NMR) lineshape into a much narrower super-imposable lineshape. We demonstrate the technique by NMR experiments, showing excellent reproducibility in every case, presenting strong evidence of recovery to certain time-unvarying field gradients and to a state of homogeneity. These findings suggest a new route for high-resolution high-temperature superconducting NMR and magnetic-resonance-imaging magnet technology.

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“…SCF substantially degrades the temporal stability and spatial homogeneity of the magnetic field and is therefore very harmful for high-resolution NMR measurements [12]. To address this problem, reducing the SCF in conventional REBCO conductor is a strategy to make REBCO applicable to high-field magnets [13][14][15][16]. Mitigation techniques that have been applied include increasing the temperature of the high-SCF sections of a magnet [17], and exceeding the coil operating current and retracting it [18].…”

Section: Introductionmentioning

confidence: 99%

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

Wang

Yan

et al. 2019

Phys. Scr.

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Due to its very high critical fields, the second-generation high-temperature superconductor (2 G HTS) has been, and is being, used in high-field magnets. However, a persistent screening current induced in the REBCO conductor under time-varying conditions distorts the magnetic field, spatially and temporally. We describe a novel REBCO conductor design composed of narrow-stacked (NS) wire, a bundle of 1 mm wide REBCO tapes. The design is based on a fundamental notion that the narrower the REBCO tape width, the smaller the screen-current field (SCF). In this paper, both experimental and simulation work were carried out to analyze SCF in a REBCO coil wound with an NS wire. We demonstrate that the critical current of NS wires can be consistent with the conventional REBCO tape to meet the application requirements. Meanwhile, NS wire indeed substantially results in small SCF, an important requirement in high-field magnets such as for NMR, MRI, and HEP that may rely on REBCO conductor.

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Study on elimination of screening-current-induced field in pancake-type non-insulated HTS coil

Cited by 15 publications

References 30 publications

Screening Current-Induced Field and Field Drift Study in HTS coils using T-A homogenous model

Screening Current-Induced Field and Field Drift Study in HTS coils using T-A homogenous model

Reproducibility of the field homogeneity of a metal-clad no-insulation all-REBCO magnet with a multi-layer ferromagnetic shim

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

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