Electromagnetic behavior of HTS coils in persistent current operations

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

doi:10.1016/j.fusengdes.2006.07.038

Cited by 11 publications

(5 citation statements)

References 9 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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“…For both B1 and b3, there was a difference in their magnitudes between patterns A and B. The method of raising the transport current above the operation current in pattern B is called the overshoot method, and it was reported to suppress the drift of the SCIFs, and reduce its magnitude [13,14]. The overshoot method was also effective in the measured magnet, and a more stable magnetic field was observed under excitation pattern B.…”

Section: A Comparison Of Drift Of Magnetic Fields Under Constant Curr...mentioning

confidence: 98%

Magnetic Field Drifts of Small HTS Dipole Magnet Under Repeated Excitation

Sogabe

Wakabayashi

Amemiya

2022

IEEE Trans. Appl. Supercond.

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Shielding-current-induced fields (SCIFs) in magnets wound with coated conductors deteriorate the field quality of the magnets. Particularly, in magnets that are excited repeatedly, and must generate time-varying magnetic fields, for example, in certain types of accelerator magnets, the influence of the temporal behavior of the SCIFs on magnetic field is quite complicated. We focused on the magnetic field drifts and conducted magnetic field measurements using a small dipole magnet wound with coated conductors cooled using a cryocooler. The magnet was operated under various patterns of excitation, and magnetic fields were measured using a rotating pickup coil, which enabled us to measure the dipole and sextupole components of the magnetic field. Numerical electromagnetic field analyses were conducted to examine the current distributions in conductors, which influenced the temporal behavior of the magnetic field.

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“…The logarithmic decay of the shielding currents is supposed to play the key role to affect the transport current in place of the coupling currents in the LTS wires [5], [6]. However, the current decay behavior of HTS coils has been evaluated only by the joint resistance and E-J characteristics of the HTS tapes, so far, on the other hand, the effect of shielding currents on the current decay behavior of the HTS coils has been discussed in [7]. In this paper, to achieve magnetic stability of 0.1 ppm/h like the LTS coils used for NMR and MRI magnets, the effect of shielding currents on magnetic stability of HTS coils are discussed using numerical analysis and experiments.…”

Section: Improvements Of Current Decay Behavior Of Hts Coils In Persimentioning

confidence: 99%

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

Hemmi

Yanagi

Seo

et al. 2007

IEEE Trans. Appl. Supercond.

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In order to improve the current decay behavior of high-temperature superconducting (HTS) coils using silversheathed Bi-2223 tapes in persistent current operations, the effect of the shielding current on the current decay behavior has been studied for magnetically levitated superconducting coils in internal ring devices. Generally, the current decay behavior of HTS coils is evaluated by the inductance of the HTS coils, the joint resistance and electric field versus current density relationship of the HTS tapes. In this paper, the effect of shielding currents in HTS tapes is discussed. It is shown that improvements of their properties of HTS tapes, which are the n-value and the critical current, are not so effective to decrease the shielding current in HTS tapes. Numerical electromagnetic analysis using finite element method and experiments have been carried out. Furthermore, improvements of the current decay behavior using excitation techniques are discussed.Index Terms-Current decay behavior, high-temperature superconducting coil, internal ring device, persistent current operation.

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Electromagnetic behavior of HTS coils in persistent current operations

Cited by 11 publications

References 9 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

Magnetic Field Drifts of Small HTS Dipole Magnet Under Repeated Excitation

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

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