Assessment of conductor degradation in the ITER CS insert coil and implications for the ITER conductors
Assessment of conductor degradation in the ITER CS insert coil and implications for the ITER conductors
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DOI：
10.1088/0953-2048/20/1/005
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发表时间：
2006
影响因子：
3.6
通讯作者：
N. Mitchell
中科院分区：
文献类型：
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作者：
N. Mitchell
由于Nb3Sn线股具有广泛的氦气接触区，在高场强(高达13T)下获得大的导体电流并对电磁干扰具有良好的稳定性，这是一种有效的管式导线中的Nb3Sn电缆。尽管ITER模型线圈成功地达到了它们的设计性能(Kato等人，2001 Fusion Eng.得了。56/57 59-70)，初步适应症(Mitchell 2003 Fusion Eng.得了。66-68 971-94)，已确认存在无法解释的业绩缺陷。最近的导体测试(Pasztor et al 2004 IEEE Trans.APPL超级棒。14 1527-30)和模特工作(Mitchell 2005 Supercond.SCI。泰克诺。18396-404)表明，这种缺陷是由于横向磁场作用下钢丝弯曲和断丝的共同作用造成的。使用新模型，对ITER CS插入线圈的大量数据库进行了重新评估。基于灯丝面积损失和n(与电场匹配的幂定律指数)的参数拟合，再加上对导体磁场梯度的更严格考虑，使得线圈行为的解释比以前的评估更一致，现在用于导体操作应变的测量时，现在符合Nb3Sn应变定标定律，包括插入线圈电流(因此操作应变)反转的条件。线圈的超导性能也显示出与最近对导体样品的测量一致的疲劳型行为(Martovetsky等人，2005，IEEE，Trans)。APPL超级棒。151367-70)。与CS插件相比，ITER导体设计已经进行了修改，通过使用钢护套提供热预压缩来降低拉伸应变水平，将空隙率从36%降低到33%，并将非铜材料增加25%，从而增加了裕度和抗退化能力。目前还没有新设计的测试结果，性能预测依赖于有限验证的模型。
Nb3Sn cable in conduit-type conductors were expected to provide an efficient way of achieving large conductor currents at high field (up to 13 T) combined with good stability to electromagnetic disturbances due to the extensive helium contact area with the strands. Although ITER model coils successfully reached their design performance (Kato et al 2001 Fusion Eng. Des. 56/57 59–70), initial indications (Mitchell 2003 Fusion Eng. Des. 66–68 971–94) that there were unexplained performance shortfalls have been confirmed. Recent conductor tests (Pasztor et al 2004 IEEE Trans. Appl. Supercond. 14 1527–30) and modelling work (Mitchell 2005 Supercond. Sci. Technol. 18 396–404) suggest that the shortfalls are due to a combination of strand bending and filament fracture under the transverse magnetic loads. Using the new model, the extensive database from the ITER CS insert coil has been reassessed. A parametric fit based on a loss of filament area and n (the exponent of the power-law fit to the electric field) combined with a more rigorous consideration of the conductor field gradient has enabled the coil behaviour to be explained much more consistently than in earlier assessments, now fitting the Nb3Sn strain scaling laws when used with measurements of the conductor operating strain, including conditions when the insert coil current (and hence operating strain) were reversed. The coil superconducting performance also shows a fatigue-type behaviour consistent with recent measurements on conductor samples (Martovetsky et al 2005 IEEE Trans. Appl. Supercond. 15 1367–70). The ITER conductor design has already been modified compared to the CS insert, to increase the margin and provide increased resistance to the degradation, by using a steel jacket to provide thermal pre-compression to reduce tensile strain levels, reducing the void fraction from 36% to 33% and increasing the non-copper material by 25%. Test results are not yet available for the new design and performance predictions at present rely on models with limited verification.