A Hybrid Magnet with a Logarithmic in Time Field Deviation

Krasnoperov, E. P.; Kartamyshev, A. A.; Puzanov, D. I.; Polushchenko, O. L.; Nizelskij, N. A.

doi:10.1007/s10948-010-0802-0

J Supercond Nov Magn

2010

DOI: 10.1007/s10948-010-0802-0

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A Hybrid Magnet with a Logarithmic in Time Field Deviation

E. P. Krasnoperov

A. A. Kartamyshev

D. I. Puzanov

et al.

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Cited by 2 publications

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References 13 publications

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“…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.…”

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“…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]. Fig.…”

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“…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]. Fig.…”

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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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Negative magnetic relaxation in superconductors

Krasnoperov

2013

EPJ Web of Conferences

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Small-Sized Hybrid Magnet with Pulsed Field Magnetization

Krasnoperov

Korotkov

Kartamyshev

2014

J Supercond Nov Magn

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A Hybrid Magnet with a Logarithmic in Time Field Deviation

Cited by 2 publications

References 13 publications

Negative magnetic relaxation in superconductors

Negative magnetic relaxation in superconductors

Small-Sized Hybrid Magnet with Pulsed Field Magnetization

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