Improvements of Current Decay Behavior of HTS Coils in Persistent Current Operations

Hemmi, T.; Yanagi, N.; Seo, K.; Bansal, G.; Takahata, K.; Mito, T.

doi:10.1109/tasc.2007.898889

Cited by 7 publications

(7 citation statements)

References 12 publications

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“…A remanent field was also reported by Gu et al [9], which was explained by a "finite thickness rectangular bar model" of the flux penetration. [10] Hemmi et al [11,12] reported a drift with time of the screening current-induced magnetic field. Recently, Amemiya and Akachi [13] conducted a general kind of numerical simulation on the steady state screening current-induced magnetic field for a 1.3 GHz NMR design.…”

Section: Introductionmentioning

confidence: 99%

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

Koyama

Takao

Yanagisawa

et al. 2009

Physica C: Superconductivity

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The screening current-induced magnetic field in the (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) insert coil proposed for a beyond 1GHz nuclear magnetic resonance (NMR) spectrometer may generate a long term field drift, resulting in a loss of field-frequency lock operation and an inability to make high resolution NMR measurements. The measured screening current-induced magnetic field of a Bi-2223 double-pancake coil exhibits a hysteresis effect at 4.2K that is reproduced by a numerical simulation based on a finite thickness rectangular superconductor bar model. The screening current-induced field at the coil center is of opposite polarity to that generated by the coil current, and thus the apparent field intensity shows a positive drift with time. On the contrary, the field at a coil end is of the same polarity as the coil field, and the apparent field intensity decreases with time. If we wait for ~1000hr after coil excitation, the field-drift rate approaches the field decay rate of the persistent current of 10-8 /hr, suitable for a long-term NMR measurement in a beyond 1GHz NMR spectrometer. 4/32

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Section: Introductionmentioning

confidence: 99%

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

Koyama

Takao

Yanagisawa

et al. 2009

Physica C: Superconductivity

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“…It involves dividing the HTS into small unit cells to analyze the current density and the magnetic field distributions in detail. Over the last few decades, various FEM methods have been proposed to analyze HTS devices, including the H-formulation [10,32,33], the A-V formulation [34,35], and the T-A formulation [36][37][38][39][40]. However, due to their underlying physical principles, these FEM methods are normally limited to studying the behavior of HTS components under pre-determined current profiles.…”

Section: Introductionmentioning

confidence: 99%

Effect of local and global screening current on the current decay in closed-loop HTS coils

Zhou,

Zhang,

Wang

et al. 2024

Supercond. Sci. Technol.

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High-temperature superconducting (HTS) coils are typically operated in a closed-loop persistent current mode to maintain their stability and minimize heat generation. However, factors such as joint resistance, flux creep, and losses due to external fields can lead to accelerated decay of the coil's current, making it challenging to achieve an effective persistent current mode. To gain insight into the current decay characteristics of HTS coils, we built a finite-element-method (FEM) based model coupled with a lumped parameter electric circuit model. The model is initially verified against the experiment of an inductive magnetized HTS coil subject to a magnetic field perpendicular to the tape surface. The results indicate that the proposed model is highly effective in predicting the current decay behavior of this magnetized HTS coil and is able to provide high accuracy. With the help of this model, we have experimentally and numerically studied the behavior of a current-carrying closed-loop HTS coil subject to external alternating fields. The HTS coil is charged by a DC power supply and then shorted using a thermally-controlled persistent current switch. The current decay behavior of the HTS coil is examined under various scenarios. The simulation results show excellent agreement with experimental data, further validating the effectiveness and versatility of the modeling strategy. The influence of both global and local screening currents on the current decay performance of the closed-loop HTS coils has been investigated. Additionally, the resulting resistance has been thoroughly characterized. These insights contribute to the knowledge of the behavior and performance of closed-loop HTS coils, facilitating their practical application

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“…Since a spacecraft cannot be equipped with refrigerants, mostly because of mass considerations, the ac loss could become a serious problem for the reliability of an HTS coil. Moreover, the induced I s could have large effects on the magnetic field distribution and the current transport characteristics of the HTS coil [12][13][14][15]. These effects must be estimated to design optimal HTS coil systems for space missions.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, understanding I s is highly important for terrestrial applications, e.g. magnetic resonance imaging, nuclear magnetic resonance imaging and cyclotrons, which require stable magnetic fields [12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigation of screening currents induced in a Bi-2223/Ag double pancake coil for space applications

Nagasaki

Nakamura

Funaki

et al. 2014

Supercond. Sci. Technol.

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We modelled screening currents (Is) induced in high-temperature superconducting (HTS) coils to develop a method for the characterization and design of HTS magnets for space applications. The analysis made use of the so-called percolation depinning and flux creep models to describe the current density versus electric field in HTS tapes. We compared model results with experimental data obtained from a Bi-2223/Ag double pancake coil. The experimental residual magnetization due to Is in the Bi-2223/Ag coil can be effectively modelled assuming an equivalent loop length of approximately 9 mm for Is in the coil. The values calculated from the method quantitatively agreed with the results for various experimental conditions. We also successfully modelled the hysteresis of the magnetization due to I s. These results demonstrate the validity of our model for Is, which considers the effects of flux creep and smaller Is loops in the multi-filamentary Bi-2223/Ag tape.

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Improvements of Current Decay Behavior of HTS Coils in Persistent Current Operations

Cited by 7 publications

References 12 publications

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

Effect of local and global screening current on the current decay in closed-loop HTS coils

Experimental and numerical investigation of screening currents induced in a Bi-2223/Ag double pancake coil for space applications

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