Dynamics and morphology of dendritic flux avalanches in superconducting films

Vestgården, Jørn Inge; Shantsev, D. V.; Galperin, Y. M.; Johansen, T. H.

doi:10.1103/physrevb.84.054537

Cited by 69 publications

(93 citation statements)

References 30 publications

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“…Since the voltage close to the branch is as high as 1 V, it follows that the electrical field can be as high as 50 kV/m. The result is in good agreement with recent simulations of the dynamics of the thermomagnetic instability by Vestgården et al, 19 where both high speed of avalanche propagation and large generated electrical field have been found. In summary, we have reported a relatively simple experimental technique, which allows imaging of dendritic avalanches in combination with measurements of the time dependence of the induced electrical voltage, on nanosecond time scales.…”

supporting

confidence: 82%

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

Mikheenko¹,

Qviller²,

Vestgården³

et al. 2013

Applied Physics Letters

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Combined voltage and magneto-optical study of magnetic flux flow in superconducting NbN films is reported. The nanosecond-scale voltage pulses appearing during thermomagnetic avalanches have been recorded in films partially coated by a metal layer. Simultaneous magneto-optical imaging and voltage measurements allowed the pulses to be associated with individual flux branches penetrating the superconductor below the metal coating. From detailed characteristics of pulse and flux branches, the electrical field in the superconductor is found to be in the range of 5-50 kV/m, while the propagation speed of the avalanche during its final stage is found to be close to 5 km/s.

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supporting

confidence: 82%

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

Mikheenko¹,

Qviller²,

Vestgården³

et al. 2013

Applied Physics Letters

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“…[28][29][30] Also, numerical simulations of the flux dynamics are a lot more computationally demanding in films compared to bulk. [31][32][33] Additional complications appear in a film with antidots, as the shielding currents then meet constrictions, and the flow must adapt to the available and often narrow bridges of superconducting material between the antidots. Hence, the current density quickly rises to the critical value, causing major rearrangements of both the current flow and the flux distribution.…”

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confidence: 99%

Mechanism for flux guidance by micrometric antidot arrays in superconducting films

et al. 2012

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Abstract"A study of magnetic flux penetration in a superconducting film patterned with arrays of micron-sized antidots (microholes) is reported. Magneto-optical imaging (MOI) of a YBa(2)Cu(3)O(x) film shaped as a long strip with perpendicular antidot arrays revealed both strong guidance of flux and, at the same time, large perturbations of the overall flux penetration and flow of current. These results are compared with a numerical flux creep simulation of a thin superconductor with the same antidot pattern. To perform calculations on such a complex geometry, an efficient numerical scheme for handling the boundary conditions of the antidots and the nonlocal electrodynamics was developed. The simulations reproduce essentially all features of the MOI results. In addition, the numerical results give insight into all other key quantities (e. g., the electrical field), which become extremely large in the narrow channels connecting the antidots." A study of magnetic flux penetration in a superconducting film patterned with arrays of micron-sized antidots (microholes) is reported. Magneto-optical imaging (MOI) of a YBa 2 Cu 3 O x film shaped as a long strip with perpendicular antidot arrays revealed both strong guidance of flux and, at the same time, large perturbations of the overall flux penetration and flow of current. These results are compared with a numerical flux creep simulation of a thin superconductor with the same antidot pattern. To perform calculations on such a complex geometry, an efficient numerical scheme for handling the boundary conditions of the antidots and the nonlocal electrodynamics was developed. The simulations reproduce essentially all features of the MOI results. In addition, the numerical results give insight into all other key quantities (e.g., the electrical field), which become extremely large in the narrow channels connecting the antidots.

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“…[31]. Material parameters typical for MgB 2 films [31,32] were used, i.e., T c = 39 K, c 0 = 35 · 10 3 J/m, κ 0 = 160 W/Km 3 , ρ n = 7·10 −8 Ωm, j c0 = 1·10 11 Am −2 , and n 0 = 50. The creep exponent was limited to n = 400 at low temperatures.…”

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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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Dynamics and morphology of dendritic flux avalanches in superconducting films

Cited by 69 publications

References 30 publications

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

Nanosecond voltage pulses from dendritic flux avalanches in superconducting NbN films

Mechanism for flux guidance by micrometric antidot arrays in superconducting films

Oscillatory regimes of the thermomagnetic instability in superconducting films

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