低温/高温复合超导体中的电流分布的研究

低温/高温复合超导体是将高温超导体部分取代复合实用低温超导体中的金属稳定材料或两者直接复合成一体,这种复合超导体具有稳定性高,工程电流密度大等优点.本文对NbTi/Bi2223高温复合超导体中的电流分布进行了理论研究,并得出液氦温度下,如果复合超导导体中,低温超导体和高温超导体具有相同的临界电流,超导体正常运行时低温超导体中的电流大于高温超导体中的电流,两者之比随运行电流的升高而降低.     

低温/高温复合超导体分流温度的定性计算

本文基于超导体幂指数模型对低温超导体和高温超导体的分流温度分别作了数值计算,计算结果与现有的分流温度估算公式结果符合的很好.本文还讨论了幂指数模型中不同n值对低温/高温复合超导体分流温度的影响,并对复合超导体分流温度做了数值计算,结果显示在相同传输电流下,低温/高温复合超导体的分流温度比传统低温超导体的分流温度高3.2K以上,这表明这种复合超导体较传统低温超导体具有更好的稳定性.     

YBCO超导线圈失超保护的研究

近来膜超导体YBCO的长尺寸化取得了较大的进展，有望在不久的将来用这种下一代的高温超导体制成超导线圈。与用低温超导体材料绕制的线圈相比，高温超导线圈可以在较高的温度下运行且较难发生失超现象。即使这样，对高温超导体失超的研究和测量也是非常有必要的。特别是膜超导体由YBCO薄膜和Ni基金属基带(比如Hastelloy合金)组成，当导体失超时有较高的电阻率。     

低温/高温复合超导磁体的研究进展

低温/高温复合超导体的研究是当前超导领域比较新的一个课题,文章介绍了低温/高温复合超导体的结构以及加工工艺,并结合相关数值模拟和实验结果对复合超导体电流分布、热传导性质、理论机理和稳定性研究等相关问题进行了讨论与探索。     

高温超导体的热力学性质的研究

以一个修正的依赖时间的金兹堡朗道理论和层状模型去研究高温超导体的热力学性质.计算各向异性超导体的热容量等一些热力学量,并且得到了超导体的熵、能、热容量的具体表达式,并与最近的实验数据进行比较,结果一致符合 关键词： 热容量 热力学量 高温超导体     

基于LabVIEW的高温超导材料特性测试实验

高温超导体临界特性的测量是近代物理实验中最为经典的实验之一,本文通过使用GM制冷机,利用Lab-VIEW虚拟仪器软件和高性能采集卡,改进了传统的测量高温超导材料临界特性的实验装置.本测试系统不仅可以测量高温超导体在不同温度下的临界电流,还可以测量其失超传播特性.该实验对于学生了解超导体特性和培养严谨的科学作风十分有益.     

高温超导体的磁化与磁滞损耗

利用三种临界态模型(Bean模型、Kim模型和指数模型),采用比较简单的方法,以Bi2223高温超导体为例,给出了平板状超导体的初始磁化曲线和磁滞回线的解析表达式.对不同温度和磁场下的磁化强度进行了编程计算,对计算结果进行讨论.利用推导的公式,讨论了温度和外加磁场对高温超导体的磁滞损耗的影响. 关键词： 磁滞损耗 磁通钉扎 高温超导体 临界态模型     

一维热传播模型下高温超导带的失超特性研究

对Bi-2223/Ag高温超导带材的失超传播特性进行了研究。测量了Bi-2223/Ag带材在有绝缘材料包裹和液氮浸泡环境下的电压变化曲线,同时利用一维热流方程模型,模拟出超导体失超传播过程中由超导态过渡到正常态的温度变化行为,同时还对传输电流和触发能量对失超传播速度的影响进行了实验研究。这些工作对高温超导磁体及电力系统的应用有着重要的参考价值。     

Hg0.9Tl0.2Ba2Ca2Cu3O8+δ在磁场下的热导

实验研究了高温超导体Hg09Tl02Ba2Ca2Cu3O8+δ的低温热导率与温度和磁场的关系,测量温度为7—20K,外加磁场为0—6T.结果表明,在不同外场下,超导体的热导率在实验温区内随温度的增加均单调增加;在固定的温度下外加磁场使超导体的热导率减小,并随外磁场的增加达到一个稳定值;热导的相对变化率κ(H)/κ(0)与磁场的关系以及热导率达到稳定值的磁场与测量温度有关.分析讨论了超导体中正常态电子在磁场下受磁通涡旋散射产生附加的热阻 关键词：     

高临界温度超导体在低温下的正常态性质

高临界温度超导体在低温下的正常态性质在超导转变温度以上，超导体处于正常态，这时电荷载流子运动伴随损耗，像通常正常金属那样存在一定的电阻．铜氧化合物高临界温度超导体（以下简称高温超导体）的正常态是二维性质的，载流子在铜氧平面内移动容易，而在二个铜氧面之...     

Bi-2223/AgAu 带材及应用进展

Bi-2223/AgAu 高温超导带材因为较低的热导率和较高的载流性能, 被认为是制备高温超导电流引线的最佳材料之一. 这篇文章简单介绍了高温超导电流引线的工作特点和不同包套 Bi-2223 带材的热导率, 在此基础上详细介绍了目前 Bi-2223/AgAu 带材和高温超导电流引线国内外研究进展, 最后展望了 Bi-2223 带材的发展趋势.     

封装材料对二代高温超导带材稳态过电流能力与拉伸性能影响的实验研究

随着二代高温超导带材从实验室走出，二代高温超导带材进入商业化大规模生产和应用阶段.针对不同的应用场景对热学、电学和力学性能的特殊要求，需要对二代高温超导带材匹配不同的后处理工艺，例如分切、镀铜以及封装等.为了解决现有常用封装材料(紫铜和不锈钢)各自的短板，本文采用铜合金材料封装，详细对比了铜银合金与黄铜与现有常用封装材料在超导带材稳态过电流能力和轴向拉伸性能的差异.发现铜银合金封装的二代高温超导带材的综合性能优于紫铜封装和不锈钢封装的二代高温超导带材.本文的研究也为实际应用中二代高温超导带材的选型提供参考.     

Analysis of current ramp for a high-temperature superconducting magnet

In this paper, an equivalent electrical circuit for response of a high-temperature superconductor (HTS) system for arbitrary time varying transport current is considered and as well as an analysis of the generated resistance losses is given. Also, for the pancake coil made with superconducting Bi-2223/AgMg tape, hysteresis behavior on the voltage-current curve is examined as a function of the current rate during ramp up and down at liquid nitrogen temperature. Behavior of voltage versus current is in good agreement with considered theory.     

Size effect in the formation and failure of stable current states in composites based on high-temperature superconductors

The influence of the transverse size of a composite wire based on a high-temperature superconductor on the dynamics of its thermoelectrodynamic properties at constant-rate current input has been studied. The physical mechanism behind the formation of stable regimes, which are characterized by the nonuniform distribution of the electric field and transport current over the cross-sectional area of the composite, has been determined. It has been shown that the critical current density of the superconducting composites determined from their current–voltage characteristic have lower and upper boundaries of electric voltages, which outline the allowable measurement range. It has been found that, when the input current completely penetrates into the composite, conditions for its stability are governed by the size effect. The essence of this effect is that conditions for current state stability in superconducting composites with the same cross-sectional area but various cross size differ. The conditions for the absence of unstable states in the composite the cross section of which is partially filled with the transport current have been formulated.     

Bi-2223复合导体直流磁场下自场损耗热稳定性分析

对于一种Bi-2223的复合导体,利用ANSYS软件,我们分析了在直流磁场下励磁过程中,自场损耗对复合导体热稳定性的影响;然后假定Bi-2223超导带内不同的损耗值,通过计算,确定了达到超导带分流温度的最小损耗值。     

Nonlinear effects of the thermal stabilization theory of applied superconducting materials

The stability of dissipative states of a Bi₂Sr₂CaCu₂O₈ applied superconducting composite cooled by liquid helium or hydrogen with continuously increasing current-voltage characteristics described by a power equation has been studied. It has been shown that, under intensive cooling conditions, special conditions of thermal stabilization can exist for applied superconducting materials (technical superconductors) if the nonlinear temperature dependences of critical current density and specific resistance of the stabilizing matrix are taken into account. First, the minimum currents of existence and propagation of a normal zone can be absent. Second, the intensive cooling of a technical superconductor substantially increases the range of stable currents in the diapason of supercritical currents. Third, during the irreversible propagation of the thermal instability, the temperature of a technical superconductor can increase under conditions close to adiabatic, despite cooling by liquid coolant. These effects should be taken into account upon determining the conditions for overheating a technical superconductor. The numerical experiments have been compared with the results that follow from the thermal stabilization theory of combined superconductors, which assumes a linear temperature dependence of critical current density of a superconductor and a step-wise transition from the superconducting to normal state.     

Electrodynamic stabilization conditions for high-temperature superconducting composites with different types of current-voltage characteristic nonlinearity

The current instability is studied in high-temperature superconducting current-carrying elements with I–V characteristics described by power or exponential equations. Stability analysis of the macroscopic states is carried out in terms of a stationary zero-dimensional model. In linear temperature approximation criteria are derived that allow one to find the maximum allowable values of the induced current, induced electric field intensity, and overheating of the superconductor. A condition is formulated for the complete thermal stabilization of the superconducting composite with regard to the nonlinearity of its I–V characteristic. It is shown that both subcritical and supercritical stable states may arise. In the latter case, the current and electric field intensity are higher than the preset critical parameters of the superconductor. Conditions for these states depending on the properties of the matrix, superconductor’s critical current, fill factor, and nonlinearity of the I–V characteristic are discussed. The obtained results considerably augment the class of allowable states for high-temperature superconductors: it is demonstrated that there exist stable resistive conditions from which superconductors cannot pass to the normal state even if the parameters of these conditions are supercritical.     

Thermal stabilization of the resistive states of superconducting composites: Quasilinear approximation

The conditions of the occurrence and development of thermal instabilities in the composite superconductor with a continuously increasing current-voltage characteristic, which is described by the power equation, have been studied. The conditions for thermal stabilization have been analyzed in the general form using dimensionless variables that keep their invariance when varying. For the local temperature disturbance, the critical energies and velocities of its irreversible propagation have been calculated. It has been proved that composites superconductors can have stable states, when the ultimate currents can be higher or lower of the conventionally preset critical current of the composite. Furthermore, superconductivity destruction at supercritical currents takes place not in the form of a stepwise transition from the superconducting to normal state, but due to the formation of thermal and electric switching waves that propagate along the composite superconductor with a constant speed. The condition for full thermal stabilization has been formulated for the superconducting composites with a power current–voltage characteristic. The results of the numerical experiments have proved that the existing theory of thermal stabilization, which assumes a stepwise superconducting–normal transition, leads to the considerable limitation of the range of the stable currents, at which a superconducting state can be kept.     

Degradation of the current-carrying capacity of low-temperature superconducting composites under the action of thermal perturbations

The stability of transport current introduced into a niobium titanium superconducting composite subjected to an external pulsed thermal perturbation has been studied. Stable states have been theoretically analyzed by solving Fourier and Maxwell equations that describe the thermoelectrodynamic states of lowtemperature superconductors with flux creep. It has been shown that, if the transport current is permanently introduced, subcritical thermal perturbations, i.e., perturbations that do not take the composite to a normal state provided that the current does not exceed the quench current, may result in the appearance of unstable current states. The higher the energy of the external thermal perturbation, the lower the instability onset current. It has been found that the degradation of the current-carrying capacity of the superconducting composite is due to intense heat release inside the superconductor, which is initiated by the thermal perturbations, and depends on the current input rate, the instant of time the current input is terminated, and cooling conditions.