Transport critical current of MgB2 wires: pulsed current of varying rate compared to direct current method
Transport critical current of MgB2 wires: pulsed current of varying rate compared to direct current method
复制标题
MgB2 线的传输临界电流：与直流法相比不同速率的脉冲电流
DOI：
10.1088/0953-2048/24/10/105009
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发表时间：
2011
影响因子：
3.6
通讯作者：
S. Dou
中科院分区：
文献类型：
--
作者：
K. W. See;X. Xu;J. Horvat;C. Cook;S. Dou
本文研究了两种不同的技术，即传统的直流（DC）电源的四探针排列和定制的三角形脉冲在不同电流变化速率下的传输临界电流（Ic）的测量。直流电法已被各种团体广泛使用和实践，但在低磁场下使用大电流时，不可避免地会产生热效应。脉冲电流法没有发热效应，但临界电流取决于脉冲电流变化率（dI/dt）。我们对不同dI/dt的脉冲电流测量表明，Ic的值与直流方法相同，但没有加热的伪影。我们的方法在低场区域特别有用，这些区域通常是直流方法无法到达的。我们还采用有限元方法（FEM）分析了超导样品在电流触点处产生的电势及其在触点周围的梯度对MgB2中热分布的时间依赖性。这个梯度被定义为样品的电流传递长度（CTL），并导致触点附近导线的焦耳加热。有限元计算结果进一步证明了直流电法在获得高输运临界电流方面的局限性。
The measurement of transport critical current (Ic) for MgB2 wires and tapes has been investigated with two different techniques, the conventional four-probe arrangement with direct current (DC) power source, and a tailored triangle pulse at different rates of current change. The DC method has been widely used and practiced by various groups, but suffers from inevitable heating effects when high currents are used at low magnetic fields. The pulsed current method has no heating effects, but the critical current can depend on the rate of the current change (dI/dt) in the pulse. Our pulsed current measurements with varying dI/dt show that the same values of Ic are obtained as with the DC method, but without the artifacts of heating. Our method is particularly useful at low field regions which are often inaccessible by DC methods. We also performed a finite element method (FEM) analysis to obtain the time dependent heat distribution in MgB2 due to the electric potential produced at the current contacts to the superconducting sample and its gradient around the contacts. This gradient is defined as the current transfer length (CTL) of the samples and leads to Joule heating of the wire near the contacts. The FEM results provide further evidence of the limitation of the DC method in obtaining high transport critical current.