本文選題：第II類超導(dǎo)體 + 金茲堡-朗道理論�。� 參考：《蘭州大學(xué)》2016年博士論文

【摘要】：超導(dǎo)體一般處于強磁場、大電流等復(fù)雜物理環(huán)境中,其臨界性能會受到外加磁場、電流和機械荷載等因素的影響。超導(dǎo)材料在傳輸電流時會產(chǎn)生交流損耗,在電磁體力作用下會發(fā)生力學(xué)變形甚至破壞。研究超導(dǎo)材料在多物理場下的臨界性能、交流損耗以及力學(xué)特性對于其實際應(yīng)用非常重要。本學(xué)位論文從宏觀角度研究了非理想第II類超導(dǎo)體的斷裂行為、磁彈性變形以及交流損耗等問題,從微觀角度分析了理想第II類超導(dǎo)體的臨界性能以及磁通流動不穩(wěn)定特性。首先,基于臨界態(tài)模型和超導(dǎo)薄帶磁通穿透理論,數(shù)值研究了含有一條中心裂紋和兩條共線裂紋的超導(dǎo)薄帶斷裂行為。采用虛擬裂紋閉合法,求得最大應(yīng)力強度因子出現(xiàn)在磁場下降階段。運用場相關(guān)的臨界態(tài)模型計算得到的最大應(yīng)力強度因子大于Bean模型得到的最大值。由于電流密度跟磁場的相關(guān)性,采用場相關(guān)的臨界態(tài)模型得到的結(jié)果比Bean模型的結(jié)果更加準確。考慮鐵磁基底對超導(dǎo)薄帶電磁響應(yīng)的影響,理論研究了超導(dǎo)/鐵磁復(fù)合雙層帶在運輸電流和垂直磁場下的磁彈性變形,并且與數(shù)值計算結(jié)果吻合。其次,對于二代高溫超導(dǎo)電纜的交流損耗,采用保角變換的方法,研究了弧形超導(dǎo)/鐵磁雙層帶以及其圓周排列形成的超導(dǎo)電纜的交流損耗規(guī)律,并且在小電流或小磁場下給出了交流損耗的解析式。重點討論了外場幅值、弧形超導(dǎo)帶寬度以及圓柱上超導(dǎo)帶的數(shù)量對超導(dǎo)電纜交流損耗的影響。最后,基于變形超導(dǎo)體的金茲堡-朗道理論,研究了應(yīng)變對第II類超導(dǎo)體上臨界磁場和下臨界磁場的影響。上臨界磁場隨著應(yīng)變的增加而減小,這與現(xiàn)有的實驗結(jié)果基本一致。進一步從理論上預(yù)測下臨界磁場隨應(yīng)變的增加而增加,并分析了耦合參數(shù)和金茲堡-朗道參量?對下臨界磁場的作用。結(jié)合二流體模型,給出了應(yīng)變與超導(dǎo)臨界溫度的關(guān)系表達式。臨界溫度隨著應(yīng)變的增加而降低,并且拉伸應(yīng)變和壓縮應(yīng)變對超導(dǎo)臨界溫度的影響是非對稱的,這與小應(yīng)變情形下的實驗結(jié)果一致。根據(jù)時間相關(guān)的金茲堡-朗道理論研究含有裂縫缺陷的細觀超導(dǎo)體的渦旋動力學(xué)和電場引起的磁通流動不穩(wěn)定性。數(shù)值模擬了相滑移線的出現(xiàn)過程及其對超導(dǎo)體內(nèi)電流-電壓特征曲線的影響。探討了裂縫傾斜角度、長度以及裂縫間距對渦旋動力學(xué)過程的影響,從而通過調(diào)整缺陷尺寸和位置以及外場大小來引導(dǎo)相滑移線并出現(xiàn)各種渦旋動力學(xué)場景。
[Abstract]:Superconductors are generally in complex physical environments such as strong magnetic field and high current. The critical properties of superconductors are affected by external magnetic field, current and mechanical load. The superconducting material will produce AC loss when transmitting current, mechanical deformation and even destruction will occur under the action of electromagnetic force. It is very important to study the critical performance, AC loss and mechanical properties of superconducting materials in multi-physical fields. In this dissertation, the fracture behavior, magnetoelastic deformation and AC loss of non-ideal type II superconductors are studied from a macroscopic perspective. The critical properties and flux instability of ideal type II superconductors are analyzed from a microscopic point of view. Firstly, based on the critical state model and the flux penetration theory, the fracture behavior of the superconducting strip with one central crack and two collinear cracks is numerically studied. By using the virtual crack closure method, the maximum stress intensity factor is obtained at the magnetic field decreasing stage. The maximum stress intensity factor calculated by using the field-dependent critical state model is larger than that obtained by the Bean model. Because of the correlation between the current density and the magnetic field, the results obtained by using the field-dependent critical state model are more accurate than those obtained by the Bean model. Considering the effect of ferromagnetic substrate on the electromagnetic response of superconducting strip, the magnetoelastic deformation of superconducting / ferromagnetic composite bilayer strip under transport current and vertical magnetic field is studied theoretically, and the results are in good agreement with the numerical results. Secondly, for the AC loss of the second generation HTS cable, the AC loss law of the arc superconducting / ferromagnetic bilayer tape and the superconducting cable formed by its circumferential arrangement is studied by conformal transformation method. At the same time, the analytical formula of AC loss is given at low current or small magnetic field. The effects of the amplitude of the external field, the width of the arc superconducting tape and the number of the superconducting tape on the cylinder on the AC loss of the superconducting cable are discussed. Finally, the effect of strain on the upper and lower critical magnetic fields of class II superconductors is studied based on the Goldsbauer-Landau theory of deformed superconductors. The upper critical magnetic field decreases with the increase of strain, which is consistent with the experimental results. It is further predicted that the critical magnetic field increases with the increase of strain, and the coupling parameters and the Kingzbau-Landau parameter are analyzed. The effect on the lower critical magnetic field. Based on the two-fluid model, the expression of the relationship between strain and superconducting critical temperature is given. The critical temperature decreases with the increase of strain, and the effect of tensile strain and compression strain on superconducting critical temperature is asymmetrical, which is consistent with the experimental results in the case of small strain. The vortex dynamics of mesoscopic superconductors with crack defects and the flux flow instability caused by electric field are studied according to the time-dependent Kingsbauer-Landau theory. The appearance process of phase slip line and its influence on the current-voltage characteristic curve in superconductor are numerically simulated. The effects of slanting angle length and spacing of cracks on the vortex dynamics are discussed. The phase slip line is guided by adjusting the size and position of the defect and the size of the external field and all kinds of vortex dynamics scenes appear.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TM26

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