Modeling the Effect of Thermal Field in Formation of Magnetic Flux Avalanches in Hard Superconductors
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Magnetothermal instabilities are one of the uncharacteristic phenomena of interest in conventional type-II as well as in high-T c superconductors. Historically, some authors undertake to analyze the nature and origin of the magnetothermal instabilities of the critical state and flux jumps phenomena in superconductors in the light of theoretical and experimental results (Wipf, Phys. Rev. 161:404, 1967; Wipf, Cryogenics 31:936, 1992; Lee at al., J. Appl. Phys. 107:013902, 2010) [1, 2]. In contrast to previous reported works which had studied the magnetic flux avalanches in hard superconductors postulating an instability criterion, in this paper, we report the development of a theoretical model for describing the magnetization curves of type-II superconductors considering the fact that the jumps should arise naturally, i.e., without the need to impose a priori conditions of instability. The model developed is applied to make numerical calculations in order to get magnetization curves of MgB2 as well as to calculate and analyze the impact of changes in the thermal field and functions that describe the critical current. We investigate the effect of initial magnetic state on generation of magnetic flux avalanches. The initial state determines the evolution of the magnetization curves and their jumps. The results obtained with the application of this model allow us to reproduce the experimental conditions with greater accuracy than that achieved with models based on unstable conditions; further, the model predicts the impact of initial nonzero fields in the formation of avalanches.
KeywordsAvalanches Hard superconductor Critical current Magnesium diboride
N.D. Espinosa-Torres acknowledges the financial support of CONACYT for the grant to carry out Ph.D. studies and the facilities given by ICUAP, CIDS, and IFUAP.
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