Magnetothermal instabilities in YBa2Cu3O7

Legrand, L.; Rośenman, I.; Simon, Ch.; Collin, G.

doi:10.1016/0921-4534(93)90747-e

Cited by 33 publications

(22 citation statements)

References 19 publications

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“…[4][5][6][7][8][9][10][11][12][13][14][15][16] Such studies are motivated by the interest from a basic point of view to understand the underlying mechanism of the instability and also in light of their potential applications ͑see the review papers 11,17 ͒. It is known that the critical state of a superconductor may become unstable when the system under appropriate conditions undergoes a small fluctuation of either the external magnetic field and/or the temperature, which is associated with a sudden puncture of magnetic flux into the volume of the superconductor, an increase of temperature in the superconductor, and the decrease or quenching of the screening current.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulations of thermomagnetic instability in high-Tcsuperconductors: Dependence on sweep rate and ambient temperature

Zhou

Yang

2006

Phys. Rev. B

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We report the results of numerical simulations of flux jumps on the basis of dynamic process of thermomagnetic interaction to the nonisothermal and nonadiabatic high-T c superconductors in the regime of thermally activated flux creep when an applied magnetic field is parallel to a slab of the high-T c superconductors. The simulations for the samples of BiSrCaCuO show that the flux jumps may occur only in the region of low ambient temperature, which is dependent upon the heat contact, and the sweep rate is greater than a lower critical value of about 20 G / s and lesser than a large one up to the order of 1 -10 T / s. It is found that the predictions of the first flux-jump field B f j1 are quantitatively in good agreement with the existing experimental data, and the temperature jumps are observed in the superconductors, corresponding to each flux jump in the magnetization loop. When the field sweep rate exceeds the large critical value for the case of the superconductor at 4.2 K, the phenomenon of experimental observations without flux jump is successfully predicted by the theoretical simulation, where the thermomagnetic interaction is smoothly circulated at a new dynamic equilibrium state in the temperature region of about 10.6-16.4 K higher than the ambient one, which is mainly dependent on the tradeoff of speeds of the dissipation energy in the slab and the heat removed into the coolant. After that, the sensitivity of the thermomagnetic instability to the parameters, such as critical current density, heat conductivity, heat transfer coefficient, critical geometrical scale, etc. is also discussed.

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Section: Introductionmentioning

confidence: 99%

Numerical simulations of thermomagnetic instability in high-Tcsuperconductors: Dependence on sweep rate and ambient temperature

Zhou

Yang

2006

Phys. Rev. B

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confidence: 99%

“…In bulk superconductors this thermomagnetic instability gives rise to abrupt displacement of large amounts of flux, so-called flux jumps, which may cause the entire superconductor to be heated to the normal state [2][3][4][5][6]. In some cases, pronounced oscillations in magnetization and temperature have been detected prior to such jumps [7,8].In film superconductors experiencing an increasing transverse magnetic fields, the thermomagnetic instability gives rise to abrupt flux entry in the form of dendritic structures rooted at the sample edge [9]. Using magnetooptical imaging [10] the residual flux distribution left in the film after such avalanche events have been observed in many superconducting materials [11][12][13][14].…”

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confidence: 99%

Oscillatory regimes of the thermomagnetic instability in superconducting films

2016

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The stability of superconducting films with respect to oscillatory precursor modes for thermomagnetic avalanches is investigated theoretically. The results for the onset threshold show that previous treatments of non-oscillatory modes have predicted much higher thresholds. Thus, in film superconductors, oscillatory modes are far more likely to cause thermomagnetic breakdown. This explains the experimental fact that flux avalanches in film superconductors can occur even at very small ramping rates of the applied magnetic field. Closed expressions for the threshold magnetic field and temperature, as well oscillation frequency, are derived for different regimes of the oscillatory thermomagnetic instability.PACS numbers: 74.25. Ha, 68.60.Dv, The irreversible electromagnetic properties of type-II superconductors are commonly explained in terms of the critical current density j c , as introduced by Bean [1]. In the corresponding critical state the distribution of magnetic flux is nonuniform and metastable. However, since j c is a decreasing function of temperature the metastable state can become unstable driven by the Joule heat generated during flux motion. In bulk superconductors this thermomagnetic instability gives rise to abrupt displacement of large amounts of flux, so-called flux jumps, which may cause the entire superconductor to be heated to the normal state [2][3][4][5][6]. In some cases, pronounced oscillations in magnetization and temperature have been detected prior to such jumps [7,8].In film superconductors experiencing an increasing transverse magnetic fields, the thermomagnetic instability gives rise to abrupt flux entry in the form of dendritic structures rooted at the sample edge [9]. Using magnetooptical imaging [10] the residual flux distribution left in the film after such avalanche events have been observed in many superconducting materials [11][12][13][14]. The experiments also show that there is a threshold magnetic field, H th , for the onset of avalanche activity, and that the unstable behavior is restricted to temperatures below a threshold value, T th , see Fig. 1. These thresholds have been explained on the basis of linear stability analysis of the nonlinear and non-local equations governing the electrodynamics of such films [15][16][17][18][19][20]. The theoretical works show that in order to trigger avalanches an electrical field in the range E = 30-100 mV/m is required.Experimentally, one finds in films of many materials, e.g., MgB 2 , Nb and NbN, that avalanches occur even when the magnetic field is ramped very slowly, e.g., below 1 mT/s [21], inducing correspondingly small E-fields. For a film placed in a magnetic field ramped at a rate of µ 0Ḣa the Bean model estimates [22] the E-field along the edge as E ∼ µ 0Ḣa w, where w is the half-width of the film. With a size of a few millimeters and a ramping rate of 1 mT/s the edge field is E ∼ 1 µV/m, i.e., several orders of magnitude below the theoretical threshold. Hence, thermomagnetic avalanches should not occur at such ramping rates, ...

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“…The magnetic instability phenomena in the high-T c superconductors were intensively studied. [2][3][4][5][6][7][8][9][10][11] At the same time, the basic peculiarities of the current instability mechanisms, which limit the currentcarrying capacity of high-T c superconductors, have not been fully investigated.…”

Section: Introductionmentioning

confidence: 99%

Sub- and overcritical stable states of composite high-Tc superconductors with different E(J) dependences and their unavoidable overheating

Romanovskii

Awaji

Nishijima

et al. 2006

Journal of Applied Physics

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To understand the underlying physical trends of the current instability in a composite high-Tc superconductor, the limiting margin of its current-carrying capacity is derived in dc magnetic fields in the framework of the macroscopic continuum approximation. A static zero-dimensional model was used to formulate the peculiarities of the nonisothermal electric field distribution in a composite in the fully penetrated current states. The power and exponential equations describing the E(J) dependences of a superconductor are used. The boundary of the allowable stable values of the electric field, current, and temperature are investigated using qualitative and quantitative models. Permissible stable values of the electric field and current, which might be lower (subcritical states) or higher (overcritical states) than those determined by the critical voltage criterion, are discussed. It is stated that the subcritical quenching electric states are more probable in the operating regimes, which are observed in the high magnetic field. The overcritical stable quantities of the electric field exist, for example, if the superconducting composite has a relatively small volume fraction of the superconductor in a composite. In the meantime, the stable current modes may be both subcritical and overcritical when the permissible value of the electric field is overcritical. As a consequence of these features, an unavoidable increase in temperature of the composite superconductor occurs before its transition to the normal state. The latter depends on a broad shape of the E(J) dependence of high-Tc superconductor and the current sharing between the superconducting core and the matrix. In the limiting case, a stable value of the composite temperature may equal the critical temperature of the superconductor. For such operating states, the criterion of the complete thermal stability condition is written taking into consideration the nonlinear character of the E(J) dependence. Simultaneously, an allowable change in temperature of the superconducting composite leads to the thermal degradation of its current-carrying capacity. It depends on the critical current density of the superconductor at bath temperature, amount of a superconductor, and cross section of a composite under fixed cooling conditions. In particular, it is shown that the currents corresponding to the instability onset do not increase proportionally with relevant increase of the superconductor’s amount. The estimates presented have general character and may be used to verify the operating states of low-Tc superconducting composite.

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Magnetothermal instabilities in YBa2Cu3O7

Cited by 33 publications

References 19 publications

Numerical simulations of thermomagnetic instability in high-Tcsuperconductors: Dependence on sweep rate and ambient temperature

Numerical simulations of thermomagnetic instability in high-Tcsuperconductors: Dependence on sweep rate and ambient temperature

Oscillatory regimes of the thermomagnetic instability in superconducting films

Sub- and overcritical stable states of composite high-Tc superconductors with different E(J) dependences and their unavoidable overheating

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