千安培、变温度、高场超导体的临界电流测量。

IF 1.5 4区 工程技术
L F Goodrich, N Cheggour, T C Stauffer, B J Filla, X F Lu
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引用次数: 6

摘要

我们回顾了在小于0.1 a到约1ka的临界电流范围内对商用超导体进行的变温度、输运临界电流(I c)测量。在过去的15年里,我们开发并使用了许多系统来进行这些测量。将描述两种具有线圈样品几何形状的示例性变温系统:仅变温探头和变温变应变探头。这些测量最重要的挑战是温度稳定性,因为大电流流过电阻样品夹具会产生大量的热量。因此,这篇综述的重要部分集中在将温度误差降低到小于±0.05 K的测量上。我们系统的一个关键特征是一个预调节器,它将液态氦转化为气体,并将气体加热到接近目标样品温度的温度。预调节器不靠近样品,它独立于样品温度进行控制。这使我们能够独立控制总冷却功率,从而在任何样品温度下微调样品冷却功率。在我们所有的变温系统中都使用了相同的一般温度控制原理,但是增加了另一个变量,例如应变,迫使在设计上妥协,并导致操作和协议的一些差异。对这些方面进行分析,以评估我们系统的协议在多大程度上可以推广到其他实验室的其他系统。我们的变温测量方法也放在测量系统设计的一般背景下,并提出了设计选择的优点和缺点。为了验证变温测量的准确性,我们比较了浸泡在液氦(“液体”或c液体)中5 K时获得的临界电流值与在相同温度下流动的氦气(“气体”或c气体)中获得的相同样品的临界电流值。这些比较表明,温度控制对电压抽头之间的超导线长度是有效的,并且这种情况适用于所有类型的样品,包括Nb-Ti, Nb3Sn和MgB2导线。液体/气体比较用于研究获得“正确”临界电流所需的变温测量方案,该临界电流假定为液态。我们还校准了温度从4 K到35 K,磁场从0 T到16 T的电阻温度计的磁阻效应。这种校准减少了变温数据中的系统误差。但这并不影响液体/气体的比较,因为在两种情况下使用相同的温度计。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

We review variable-temperature, transport critical-current (I c) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium ("liquid" or I c liq) at 5 K to those measured on the same specimen in flowing helium gas ("gas" or I c gas) at the same temperature. These comparisons indicate the temperature control is effective over the superconducting wire length between the voltage taps, and this condition is valid for all types of sample investigated, including Nb-Ti, Nb3Sn, and MgB2 wires. The liquid/gas comparisons are used to study the variable-temperature measurement protocol that was necessary to obtain the "correct" critical current, which was assumed to be the I c liq. We also calibrated the magnetoresistance effect of resistive thermometers for temperatures from 4 K to 35 K and magnetic fields from 0 T to 16 T. This calibration reduces systematic errors in the variable-temperature data, but it does not affect the liquid/gas comparison since the same thermometers are used in both cases.

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来源期刊
自引率
33.30%
发文量
10
期刊介绍: The Journal of Research of the National Institute of Standards and Technology is the flagship publication of the National Institute of Standards and Technology. It has been published under various titles and forms since 1904, with its roots as Scientific Papers issued as the Bulletin of the Bureau of Standards. In 1928, the Scientific Papers were combined with Technologic Papers, which reported results of investigations of material and methods of testing. This new publication was titled the Bureau of Standards Journal of Research. The Journal of Research of NIST reports NIST research and development in metrology and related fields of physical science, engineering, applied mathematics, statistics, biotechnology, information technology.
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