In the critical state model, the critical current, , of a superconductor defines the upper limit of dissipation-free current flow. However conventional transport measurements of practical superconductors rely on the detection of a voltage drop along the length of the conductor. This requires that the superconductor has entered the dissipative regime, and hence inherently over-estimates the current at which geometric saturation occurs. Nonetheless, the convenience of the 1 V cm⁻¹ criterion means that it has become the widely adopted definition of transport . Here, we present an alternative definition for the transport critical current of a superconducting tape under self-field conditions, which is based on the concept of geometric current saturation across the full cross-sectional area. This saturation threshold can be experimentally determined through simple Hall sensor measurements of the evolving perpendicular magnetic field at the tape surface. The surface field exhibits a signature transition when the transport current increases beyond the current-saturation threshold. We present an analytical model which describes this effect and defines the critical saturated current as a function of . This definition is first validated using finite element (FE) modelling, and then experimentally demonstrated through measurements on a variety of commercial REBCO and Bi-2223 tapes of differing widths. It is found that the 1 V cm⁻¹ criterion consistently leads to an overestimation of the saturated critical current by ∼15% in REBCO tapes, and up to 30% in a Bi-2223 tape. FE modelling indicates that this overestimate is most prominent in superconductors exhibiting a low n-value (i.e. n ≲ 20). A key advantage of the measurement approach presented here is that it allows the unambiguous measurement of a transport value to be completed at lower currents, without entering the dissipative region in which sample damage can occur. There are also implications as to the correct choice of value which should be employed within the well-known Norris and Brandt equations for AC loss.

在临界状态模型中，超导体的临界电流定义了无耗散电流的上限。然而，实际超导体的传统传输测量依赖于沿导体长度的电压降的检测。这要求超导体已进入耗散状态，因此固有地高估了发生几何饱和的电流。尽管如此，1V cm ^-1标准意味着它已成为广泛采用的传输定义。在这里，我们提出了在自场条件下超导带传输临界电流的另一种定义，该定义基于整个横截面积上的几何电流饱和的概念。这个饱和阈值可以通过简单的霍尔传感器测量磁带表面上演化的垂直磁场来实验确定。当传输电流增加超过电流饱和阈值时，表面场表现出特征转变。我们提出了一个分析模型，该模型描述了这种效应，并将临界饱和电流定义为. 该定义首先使用有限元 (FE) 建模进行验证，然后通过对各种不同宽度的商业 REBCO 和 Bi-2223 胶带的测量进行实验证明。发现 1V cm ^-1标准始终导致在 REBCO 胶带中高估饱和临界电流约 15%，在 Bi-2223 胶带中高估高达 30%。有限元建模表明，这种高估在表现出低n值（即n ≲ 20）的超导体中最为突出。此处介绍的测量方法的一个关键优势是，它允许在较低电流下完成传输值的明确测量，而不会进入可能发生样品损坏的耗散区域。对于在众所周知的交流损耗的Norris和Brandt方程中应该采用的值的正确选择也有影响。