关于上临界场和不可逆场测量方法标准化的思考

本文回顾了超导体上临界场强度 H c2 和不可逆场强度 Hirr 的相关物理背景及定义, 汇总了不同测量技术的原理和方法, 以及影响测量不确定度的主要因素, 指出 H c2 和 Hirr 测量的根本区别在于前者不应在测量中引入磁通运动相关的能量损耗. 分析了 H c2 和 Hirr 测量的难点, 介绍了以往国际上对建立单一测量方法标准所做的努力, 总结归纳了不同方法测量结果不一致的根本原因, 在于测量条件决定的测量分辨率以及人为设定的不同判据.因此如果可以精确控制测量条件和判据, 四引线电阻法最简便因而最适宜选做标准化的测量方法. 考虑到高场强磁体在国内实验室的普及程度, 现阶段有可能实现标准化的只有液氦冷剂浸泡下变磁场测量 Nb-Ti 复合超导线的J c 从而确定 Hirr(4.2 K)

Consideration on Standardization of Measurement Method for Upper Critical Field and Irreversibility Field

The physical background and definition of upper critical field strength H c2 and irreversibility field strength Hirr of superconductors are reviewed. The principles and methods of different measurement techniques and the main relevant factors affecting the measurement uncertainty of each method are summarized. The fundamental difference between H c2 measurement and Hirr measurement is that no energy dissipation owing to flux motion shall be introduced in the former. The difficulties of H c2 and Hirr measurement are analyzed, and the previous efforts to establish international standards are discussed. The inconsistent results obtained by using different methods lie in the varied measurement resolution and different criteria selected. Therefore, if the measurement conditions can be accurately controlled and the criteria fixed, the four-probe transport method is the simplest and most convenient for standardized measurement. Considering the current status of high field capacity in domestic laboratories, now it is only plausible to standardize the measurement of Hirr of Nb-Ti composite wires immersed in liquid helium, by measuring J c values in varied magnetic fields.