Numerical techniques to evaluate levitation force and stable equilibrium of htsc flywheel

Tsuchimoto, M.; Kojima, T.; paki, H.; Honma, Tetsuo

doi:10.1016/0964-1807(94)90044-2

Cited by 14 publications

(10 citation statements)

References 13 publications

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“…Equation (4) is transformed to an integral equation and is solved by the boundary element method. Details of the formulation were precisely reported in the previous paper [9]. Self-consistent solutions, which satisfy nonlinear (2) at each time step, are obtained by using numerical techniques in iterative calculations [9]- [11].…”

Section: A Field-cooled Magnetizationmentioning

confidence: 99%

“…Details of the formulation were precisely reported in the previous paper [9]. Self-consistent solutions, which satisfy nonlinear (2) at each time step, are obtained by using numerical techniques in iterative calculations [9]- [11]. The current density in the th step is corrected as follows with the electric field in (5) (6) where is the convergence condition and is set to a small value according to the convergence of the solution.…”

Section: A Field-cooled Magnetizationmentioning

confidence: 99%

“…On the other hand, there were many reports about macroscopic numerical simulation of the HTS [6]- [8], and authors also studied electromagnetic phenomena of a bulk HTS [9]- [11]. Nonlinear constitutive relationships between shielding current density and electric field are important in the macroscopic numerical evaluation [6].…”

Section: Introductionmentioning

confidence: 99%

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Macroscopic numerical evaluation of heat generation in a bulk high Tc superconductor during pulsed field magnetization

Tsuchimoto

Morikawa

1999

IEEE Trans. Appl. Supercond.

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Pulsed-field magnetization of a bulk high Tc superconductor (HTS) is evaluated by using a macroscopic numerical simulation code. Local heat generation in the HTS during the pulsed-field magnetization is discussed to clarify the dynamic magnetization process. Nonlinear dependence of shielding current on the dynamic magnetic field is considered by using the flux flow-creep model. Dependence of flow resistivity on the magnetic field and temperature are also evaluated with the Bardeen-Stephen and the Tinkham models. It is numerically confirmed that reported experimental results are due to a decrease of the shielding current caused by local heat generation.

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Section: A Field-cooled Magnetizationmentioning

confidence: 99%

Section: A Field-cooled Magnetizationmentioning

confidence: 99%

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Macroscopic numerical evaluation of heat generation in a bulk high Tc superconductor during pulsed field magnetization

Tsuchimoto

Morikawa

1999

IEEE Trans. Appl. Supercond.

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“…As a first approximation, we assume that immediately after the pulse the local temperature depends linearly on the cylinder's radius. Thus, T increases linearly from the inner edge of superconducting cylinder to the outer one, as it turns out in many calculations [8,9]. Assuming that the experiments are carried out at liquid nitrogen temperature, the radial heating T can be written as…”

mentioning

confidence: 91%

“…By analogy with the superconducting currents we determine the field relaxation rate in the same form as (5). Accordingly, from (4) and (7) we obtain an expression for the relative relaxation rate of the trapped field in a hollow cylinder (8) In order to compare our model with experimental data we calculated the dependence of S (R m ) / S 78 for a hollow cylinder, in which R 1 = 0.8 cm, and R 2 = 1.8 cm. Annuli with such dimensions have been studied in [4].…”

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Negative magnetic relaxation in superconductors

Krasnoperov

2013

EPJ Web of Conferences

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Abstract. It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation) if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.Advances in the synthesis of large melt grown crystals of high-temperature superconductors (HTS) based on Y (Re) BaCuO [1] led to extensive investigations of their superconducting properties with a view of practical applications. One of these applications is creating magnetic systems for compact EPR and NMR spectrometers. The superconductors are magnetized either in a static magnetic field (FC) which is switched off afterwards, or using a pulse method. The pulsed field magnetization (PFM) method is the preferred one because of low power consuming and simplicity. The main disadvantage of HTS materials is a reduction of the critical current J c with time, which is caused by magnetic flux creep. Therefore, the trapped magnetic moment decreases with time, regardless of the magnitude of the magnetization, when superconductors are slowly (isothermally) magnetized. Generally this process is linear in a logarithmic time scale [2]. On the other hand, after a short PFM of HTS one can observe not only the decrease of the magnetic moment, but also its growth [3,4]. The growth of the trapped magnetic field is observed in tablets, as well as in annuli if they are not completely magnetized by a pulsed magnetic field. This effect can be called as a negative relaxation according to the accepted definition of the relaxation rate [2]. The negative relaxation is observed when the trapped field is less, by 10-20%, than the maximal value B max . Figure 1 shows the experimental dependence of the normalized trapped field B(t) / B max in the gap of 2mm between two superconducting annuli (manufactured by the method described in [5]) after the action of magnetizing pulses of 10 ms duration. The pulse amplitude was gradually increased during the multi-pulsed field magnetization (multi-PFM). The trapped field is normalized to the maximal attainable value of B max ≈ 0,7T. At the initial stage of magnetization, when B / B max << 0.75 (see figure 1C), we observed a jump in the trapped field just after a field pulse, followed by a continuous growth of B with the time. Figure 1B shows the trapped field data after pulses for intermediate magnetization. In this case the rate of the magnetization growth is essentially reduced and after the jump the field changes only slightly with time. In large fields (figure 1A) near the maximum magnetization (B / B max > 0.9), the field B decreases with time. Note that reducing of the trapped field is typical for superconductors (a positive relaxation of the magnetization), in contrast to the negative relaxation observed at the initial part of the multi-PFM.It is shown below that the negative r...

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Levitation Applications of High-Temperature Superconductors

Hull

2004

High Temperature Superconductivity 2

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Numerical techniques to evaluate levitation force and stable equilibrium of htsc flywheel

Cited by 14 publications

References 13 publications

Macroscopic numerical evaluation of heat generation in a bulk high Tc superconductor during pulsed field magnetization

Macroscopic numerical evaluation of heat generation in a bulk high Tc superconductor during pulsed field magnetization

Negative magnetic relaxation in superconductors

Levitation Applications of High-Temperature Superconductors

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