Nature of the low magnetization decay on stacks of second generation superconducting tapes under crossed and rotating magnetic field experiments

Baghdadi, Mehdi; Coombs, Tim

doi:10.1038/s41598-018-19681-8

Cited by 32 publications

(42 citation statements)

References 27 publications

(48 reference statements)

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“…with t i and t f being the time at the beginning and end of the demagnetization process, respectively. For our configuration, which is similar to that in other works [5,24,25,28], the error regarding this quantity is more strict than for the trapped field (table II) in errors below 20 % for ripple fields of 100 mT or below.…”

Section: G Cross-field Demagnetization: Measurements and Modellingsupporting

confidence: 84%

“…The ). This process can be explained by the Bean model of the infinite thin strip [27] or other numerical 2D modelling [5,25]. In our stack, the penetration front contains both the penetrates from the top and bottom of each individual tape.…”

Section: Trapped Magnetic Field In the Stack Of Tapesmentioning

confidence: 99%

“…Then, a long stack traps 50 % more flux than an array of bulks of the same width as the stack for each bulk. In addition, the stack enables to interlay sheets of other materials to enhance physical properties: metal layers enhance thermal properties; and soft ferromagnetic layers enhance the trapped field and reduce cross-field demagnetization, at least for stacks as stand-alone objects and below the saturation for the magnetic material [5].…”

Section: Introductionmentioning

confidence: 99%

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Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Kapolka¹,

Pardo

Grilli³

et al. 2019

Supercond. Sci. Technol.

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Stacks of superconducting tapes can trap much higher magnetic fields than conventional magnets. This makes them very promising for motors and generators.However, ripple magnetic fields in these machines present a cross-field component that demagnetizes the stacks. At present, there is no quantitative agreement between measurements and modeling of cross-field demagnetization, mainly due to the need of a 3D model that takes the end effects and real micron-thick superconducting layer into account. This article presents 3D modeling and measurements of cross-field demagnetization in stacks of up to 5 tapes and initial magnetization modeling of stacks of up to 15 tapes. 3D modeling of the cross-field demagnetization explicitly shows that the critical current density, J c , in the direction perpendicular to the tape surface does not play a role in cross-field demagnetization. When taking the measured anisotropic magnetic field dependence of J c into account, 3D calculations agree with measurements with less than 4 % deviation, while the error of 2D modeling is much higher. Then, our 3D numerical methods can realistically predict cross-field demaga This article has been published in Supercond. Sci. Technol. with netization. Due to the force-free configuration of part of the current density, J, in the stack, better agreement with experiments will probably require measuring the J c anisotropy for the whole solid angle range, including J parallel to the magnetic field.the probe is at least 10 mV/T. Cross-field demagnetization consists on the following three main steps: magnetization by field cooling (FC) method, relaxation time and cross-field demagnetization. The detailed process is the following:• The sample is placed into the electromagnet at room temperature.• The electromagnet is ramped up to 1 T.• The sample is cooled down in liquid nitrogen bath at 77 K.• The electromagnet is ramped down with ramp rate 10 mT/s. 400 405 410 415 420 425 B t /B 0 [-] t [s] cal 50 mT cal 100 mT cal 150 mT cal 50 mT n(B,θ) cal 100 mT n(B,θ) cal 150 mT n(B,θ) (b) FIG. 19: (a) The n(B, θ) measured data on a 4 mm wide SuperOx tape, measured in Bratislava by the set-up in [46]. (b) The comparison of calculation with constant n=30 and n(B, θ) dependence, both cases use J c (B, θ) dependence. Using n(B, θ) slightly reduces the demagnetization rate for a few number of cycles, but later on it is increased slightly.

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Section: G Cross-field Demagnetization: Measurements and Modellingsupporting

confidence: 84%

Section: Trapped Magnetic Field In the Stack Of Tapesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Kapolka¹,

Pardo

Grilli³

et al. 2019

Supercond. Sci. Technol.

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“…For large ripple fields, superconducting bulks face more demagnetization as compared to the HTS stacks, and can lose upto 50 percent of magnetization after just 1 cycle of applied cross field [23]. The demagnetization is also larger for rotating fields as compared to the cross fields [9].The demagnetization of the stacks is directly dependent to the ripple field amplitude and ripple field frequency, and increases linearly with the ripple field amplitude. This is due to the direct proportionality of DC electric field generated inside the superconductor to the ripple field amplitude according to Brandt and Mikitik theory [2,24], atleast for high ripple fields.…”

Section: Introductionmentioning

confidence: 99%

Time constant of the transverse-field demagnetization of superconducting stacks of tapes

Dadhich¹,

Pardo²,

Kapolka³

2020

Supercond. Sci. Technol.

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Stacks of REBCO tapes can trap large amounts of magnetic fields and can stay magnetized for long periods of times. This makes them an interesting option for major engineering applications such as motors, generators and magnetic bearings. When subjected to transverse alternating fields, superconducting tapes face a reduction in the trapped field, and thus it is the goal of this paper to understand the influence of all parameters in cross field demagnetization of stacks of tapes. Major parameter dependencies considered for the scope of this paper are ripple field amplitude, frequency, tape width, tape thickness (from 1 to 20 µm), and number of tapes (up to 20). This article also provides a systemic study of the relaxation time constant τ , which can be used to estimate the cross-field demagnetization decay for high number of cycles. Modeling is based on the Minimum Electro-Magnetic Entropy Production method, and it is shown that the 2D model gives very accurate results for long samples when compared with 3D model. Analytical formulas for large number of cycles have been devised. The results show that when the ripple field amplitude is above the penetration field of one tape, the stack always fully demagnetizes, roughly in exponential decay. Increasing the number of tapes only increases the relaxation time. The formulas derived also hold when validated against numerical results, and can be used for quick approximation of decay constant. They also show that the cause of the decreases of cross-field demagnetization with number of tapes is the increase in the self-inductance of the magnetization currents. The trends and insights obtained for cross field demagnetization for stacks are thus very beneficial for engineers and scientists working with superconducting magnet design and applications.

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“…Thus, we present a comprehensive computational study of the profiles of current density, magnetic flux features, and AC losses of racetrack coils with 20 turns of commercially available 2G-HTS tapes (SCS4050), 18 either perfectly wound or with a maximum lateral misalignment factor (δ m ) of 100 µm between adjacent turns, both subjected to AC trans-port currents of different amplitudes (see Fig.1). The numerical simulations are performed within the framework of the celebrated 2D H-formulation, [19][20][21][22] implemented in COMSOL Multiphysics 5.3a, 23 together with what is up to now the most general material law for describing the E-J properties of the 2G-HTS tapes at constant temperature, which extends the conventional Kim's critical state model to an experimentally validated magneto angular dependent E-J power law 18 .…”

Section: Introductionmentioning

confidence: 99%

Local electromagnetic properties and hysteresis losses in uniformly and non-uniformly wound superconducting racetrack coils

Robert

Fareed

2019

Journal of Applied Physics

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A noteworthy physical dependence of the hysteresis losses with the axial winding misalignment of superconducting racetrack coils made with commercial Second Generation High Temperature Superconducting (2G-HTS) tapes is reported. A comprehensive study on the influence of the turn-to-turn misalignment factor on the local electromagnetic properties of individual turns, is presented by considering six different coil arrangements and ten amplitudes for the applied alternating transport current, I a , together with an experimentally determined function for the magnetoangular anisotropy properties of the critical current density, J c (B, θ), across the superconducting tape. It has been found that for moderate to low applied currents I a ≤ 0.6 I c0 , with I c0 the self-field critical current of individual tapes, the resulting hysteretic losses under extreme winding deformations can lead to an increase in the energy losses of up to 25% the losses generated by a perfectly wound coil. High level meshing considerations have been applied in order to get a realistic account of the local and global electromagnetic properties of racetrack coils, including a mapping of the flux front dynamics with well defined zones for the occurrence of magnetization currents, transport currents, and flux-free cores, what simultaneously has enabled an adequate resolution for determining the experimental conditions when turn-to-turn misalignments of the order of 20 µm-100 µm in a 20 turns 4 mm wide racetrack coil can lead not only to the increment of the AC losses but also to its reduction.In this sense, we shown that for transport current amplitudes I a > 0.7 I c0 , a slight reduction in the hysteresis losses can be achieved as a consequence of the winding displacement which is at the same time connected with the size reduction of the flux free core at the coil central turns. Our findings can be used as a practical benchmark to determine the relative losses for any 2G-HTS racetrack coil application, unveiling the physical fingerprints that possible coil winding misalignments could infer.

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Nature of the low magnetization decay on stacks of second generation superconducting tapes under crossed and rotating magnetic field experiments

Cited by 32 publications

References 27 publications

Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Cross-field demagnetization of stacks of tapes: 3D modelling and measurements

Time constant of the transverse-field demagnetization of superconducting stacks of tapes

Local electromagnetic properties and hysteresis losses in uniformly and non-uniformly wound superconducting racetrack coils

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