Critical current measurement with spatial periodic bending imposed by electromagnetic force on a standard test barrel with slots

Abstract

We have developed and validated a straightforward and fast method to investigate the response of technological superconducting strain sensitive wires ͑e.g., Nb 3 Sn͒ to a spatial periodic bending strain. In the present concept of cabled superconductors for application in nuclear fusion reactors the wires are twisted and cabled in several stages. When subjected to transverse electromagnetic forces after charging the magnet, the individual strands are subjected to spatial periodic bending with wavelengths in the order of 5 -10 mm. Several apparatuses are presently under development to study the effect of bending on the transport properties, i.e., the voltage-current transition in terms of critical current ͑I c ͒ and n value. We propose a supplementary simple method to investigate the influence of bending strain by using a spatial periodic wire support on a broadly used standard I c measurement barrel in combination with a Lorentz force. The bending force ͑BI͒ is varied by changing the applied field B. The peak bending strain in the Nb 3 Sn filaments is determined by the amplitude of the bending deflection, which is deduced from the mechanical axial tensile stress-strain properties of the wire. Three different spatial periodic wavelengths are applied and the results are in good agreement with the predictions. In addition we found a good agreement with results obtained by a more advanced experiment, named TARSIS, which is described briefly. The "barrel-with-slots" method can be applied easily and straightforward with minor effort and cost in laboratories having a standard I c measurement facility for superconducting wire.

Transverse load optimization in Nb3Sn CICC design; influence of cabling, void fraction and strand stiffness

“…In the TARSIS setup, the influence of various loads and deformations (axially tensile, bending strain, contact load from crossing strands or homogeneous transverse load) that frequently occur in a CICC, are studied with different probes [2,[12][13][14][15][16][17][18][19][20][21]. Over the last few years, there is an increasing interest to study the impact of mainly bending strain on the transport properties of superconducting wires [7,22,23].…”

“…While bending is broadly studied, the impact of local transverse loads at strand crossings has hardly received any attention, even though these stresses can be quite severe in the part of the cable cross-section where the load accumulates. The design of the TARSIS setup is presented in [12] while various experimental results obtained on powder in tube-, internal tin-and bronze-processed Nb 3 Sn wires are reported in [13][14][15][16][17][18][19][20][21].…”

Effective Low Magnetic Field Jc(B) Scaling of ITER Nb3Sn Strands by Magnetization and Critical Current Measurements

“…The employed sequence of the maximum fields B m is: 0.2, 0.3, 0.4, 0.5, 0.7, 1.0, 2.0, 3.0, 5.0, 7.0, 8.0, and 9.0 T. The ramp rate is r = 0.07 T/min for the sweeping field with a maximum magnitude less than or equal to 2.0 T, and r = 0.5 T/min for the higher field magnitudes. The testing temperature is also 4.2 K [11]. The magnetization of the strand is derived from the magnetic moment measured and the volume of the sample.…”

Research progress on the mechanical behavior of the cable in conduit conductor for the international thermonuclear experimental reactor project

“…Nunoya等人 [34] 和Koizumi等人 [35] 以及荷兰特温特大 学Nijhuis等人 [36,37] [34] . 由于该模型将股线间搭接长度取 为定值, 这相当于给定了Nb 3 Sn股线的最大曲率半径 上限以及层间横向挤压力累积上限, 与现实绞缆受 力情形不符, 这也是模型预测的横向等效模量与实 验测试结果相去甚远的原因 [39] .…”