Dynamic Instabilities and Current-Voltage Curves of Polycrystalline Superconducting Y1Ba2Cu3O7−x /Ag

Ainslie

2020

Flux avalanches induced from thermomagnetic instability are crucial challenges for the application of superconducting thin film devices. In this paper, flux avalanches in a type-II superconducting thin film exposed to a transient AC magnetic field are numerically simulated by solving the coupled nonlinear Maxwell's equations and the heat diffusion equation based on the fast Fourier transform (FFT) method. The dependence of the threshold magnetic field on the ambient temperature, film thickness and magnetic field ramp rate are obtained through these numerical simulations, which show good agreement with experimental results. A linear increase in the threshold field as the film thickness increases and a nonmonotonic increase in the threshold field as the ambient temperature increases have also been found. Our numerical results demonstrate that the threshold field decreases exponentially as the ramp rate increases. Flux avalanche patterns observed in magneto-optical imaging (MOI) measurements for a film exposed to an AC magnetic field are reproduced. The hysteresis magnetization and maximum temperature jump curves are also illustrated. We find that fingering instability plays an important role in the thermomagnetic response of superconducting thin films under transient AC magnetic fields, especially for high magnetic field ramp rates.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical simulation of flux avalanches in type-II superconducting thin films under transient AC magnetic fields

Ainslie

2020

“…At the propagation front the temperature can even rise above the superconducting transition temperature [15]. Random occurrence of the flux avalanches and accompanied dramatic events add noise to the electromagnetic signal of the superconducting electronic devices in service [16,17]. The large temperature change may cause significant thermal strain [18,19] or microscale damage [20], and even the melting of the superconducting film when the local temperature rises high enough [21].…”

Section: Introductionmentioning

confidence: 99%

Influences of non-uniformities and anisotropies on the flux avalanche behaviors of type-II superconducting films

Yong

Zhou

2016

In this paper, the anisotropic flux avalanche processes in thin square-shaped type-II superconducting films are numerically investigated by solving the coupled nonlinear Maxwell’s equations and the thermal diffusion equations. Influences of the non-uniformities and intrinsic critical current density anisotropies originate from the manufacturing process are considered in the simulation. In addition, we also studied the effect of the extrinsic anisotropy induced by the in-plane magnetic field. The results demonstrate that the non-uniformities and anisotropies of the critical current density play significant roles in the flux avalanche process of the thin film superconductors. Slight anisotropy (either intrinsic or extrinsic) can dramatically change the propagation direction of avalanches in the superconducting film, which is consistent with the experimental results. Simulations on the thin square-shaped isotropic superconducting films show that the threshold magnetic field for the flux avalanches increases with the angle between the applied field and the superconducting film-plane. In addition, the flux avalanche patterns change with the angular variation of the in-plane component of external magnetic field. When the in-plane magnetic field component is along the diagonal lines of the superconducting square, symmetric flux avalanche penetration patterns occur to the film.

“…The thermomagnetic breakdown that induces dendritic flux avalanches is commonly found among superconductors at low temperatures [10,11]. Experiments using magneto-optical imaging (MOI) have revealed that flux avalanches take place in numerous superconducting materials like YBa 2 Cu 3 O 7−x [12][13][14][15], MgB 2 [10,16], Nb 3 Sn [17][18][19], YNi 2 B 2 C [20], Pb [21][22][23], NbN [24], etc. The propagation of these avalanches is extremely fast, with velocities up to hundreds of kilometers per second [7].…”

Section: Introductionmentioning

confidence: 99%

Dendritic flux avalanches and the accompanied thermal strain in type-II superconducting films: effect of magnetic field ramp rate

Yong

Zhou

2015

Dendritic flux avalanches and the accompanying thermal stress and strain in type-II superconducting thin films under transverse magnetic fields are numerically simulated in this paper. The influence of the magnetic field ramp rate, edge defects, and the temperature of the surrounding coolant are considered. Maxwell's equations and the highly nonlinear E-J powerlaw characteristics of superconductors, coupled with the heat diffusion equation, are adopted to formulate these phenomena. The fast Fourier transform-based iteration scheme is used to track the evolution of the magnetic flux and the temperature in the superconducting film. The finite element method is used to analyze the thermal stress and strain induced in the superconducting film. It is found that the ramp rate has a significant effect on the flux avalanche process. The avalanches nucleate more easily for a film under a large magnetic field ramp rate than for a film under a small one. In addition, the avalanches always initiate from edge defects or areas that experience larger magnetic fields. The superconducting films experience large thermal strain induced by the large temperature gradient during the avalanche process, which may even lead to the failure of the sample.