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

Abstract

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.

Vortex avalanches in a Pb-porous glass nanocomposite

“…At 5.5 K the jumps are seen on the secondary magnetization, but still do not occur on the virgin magnetization, in agreement with the predictions of Ref. 40. Such a difference between the experimental virgin and secondary magnetizations was not reported in Ref.…”

“…However, at a temperature of 1.8 K, the magnetic jumps differ remarkably from those predicted in Ref. 40. Very small, incomplete, and rapid jumps such as noise are seen only in the central part of the hysteresis loop, while at higher fields the flux jumps remain full with a much lower periodicity.…”

“…By comparing the results obtained with the numerical predictions of Ref. 40, one can see good agreement of the calculations with the behavior of the jumps on the loop wings, which follows the general ideas about the evolution of magnetic instabilities that, when the adiabatic approximation is no longer valid, the system is characterized with an average temperature that different from the bath temperature, and some kind of dynamic equilibrium is established between the heat removed to the bath and that produced in the sample by moving vortices. The shape of the smooth experimental hysteresis loop at low fields does not match with the numerically obtained ones, in particular, it does not show a peak near zero field accompanied with a single flux jump.…”

Magnetization jumps in a lead-porous glass composite: Experiment and simulation

“…Closer to the surface the modified profile corresponds to the bath temperature while deeper in the slab it remains frozen and corresponds to the profile which was setup immediately after the jump at T 1 . In further calculations of subsequent jumps, x 0 in the instability condition (16) should be considered as the intersection point of these two parts of the modified profile.…”

“…More general numerical approach which takes into account the kinetics of heat exchange with the bath was suggested in Ref. 16. For thin films, however, dendrite and branched fingerlike patterns as well as feather-shaped flux fronts 2,17-20 were observed instead of homogeneous Bean magnetic profiles.…”