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

Abstract

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.

Magnetic flux penetration in Nb superconducting films with lithographically defined microindentations

“…We also show that the curvature of the d-lines emerging from the defect decreases as the temperature is increased. Moreover, in opposition to what has been repeatedly suggested based on the Bean model, [2][3][4]13 indentations do not seem to be distinguished places for the nucleation of flux jumps but rather the opposite, a place where flux avalanches will not take place. The extension of our results to samples with defects inside rather than at the border of the films is straightforward.…”

Analysis of Observed Voltage Oscillations in Silver Doped High Temperature Superconductor YBCO

“…It has been suggested that the system of weakly pinned vortices resembles the pinned CDW state. Experimental results on charge density waves gives that coherent current or voltage oscillations appear along the sample after reaching the threshold value of the driving voltage or current [15][16][17][18][19]. In the present study, we suppose that a physical mechanism regarding the density instabilities of flux lines (or self magnetic field (SMF) lines) can be introduced as a possible mechanism for coherent voltage oscillations.…”

Flux avalanche in a superconducting film with non-uniform critical current density

“…Our numerical simulation region is 2 L × 2 L, where L = 1.3a [17]. The simulation region is discretized with 512 × 512 equidistant grids.…”

“…Researchers have done much work on different superconducting materials to understand the characteristics of flux avalanche. Flux avalanche is closely related to the external magnetic field [13,14], the geometry of the superconducting material [15,16], the field ramp rate [17] and the environmental temperature [18]. Baziljevich et al [19] studied the dendritic instability in a YBa 2 Cu 3 O 7-d film at very high magnetic ramp rates.…”

“…At a higher environmental temperature, the location of the first avalanche is related to the fluctuations due to a random disturbance. Jing et al [17,35,36] studied the flux avalanche and the thermal strain in type-II superconductors with different applied magnetic field ramp rates. During the fabrication of a thin film, the flux pinning is enhanced locally with graded pinning landscapes [37].…”