Nb₃Sn superconductor is of significant interest for applications in constructing high-field magnets beyond the limit of NbTi. However, its critical current density decreases rapidly at high magnetic fields ( > 12 T) and the state-of-the-art level of Nb₃Sn superconductors still cannot meet the requirements of the planned future accelerator magnets. The primary flux pinning centers for Nb₃Sn wire mainly arise from the grain boundaries (GBs). In the present paper, we theoretically investigate, through time-dependent Ginzburg-Landau theory and with graphics-processing unit parallel technique, the vortex pinning and the critical current density in large-scale polycrystalline Nb₃Sn superconductor by varying the pinning potential of GB and grain size at various magnetic fields. Unlike the conventional dot-like pinning systems, it is found that the critical current is not a monotonous function by suppressing the superconductivity of the GBs. The optimal pinning potential of GB for maximum critical current density strongly depends on magnetic fields. Furthermore, we find that the critical current density can be significantly enhanced by reducing grain size at low magnetic fields, while increase of critical current density cannot always be observed at high magnetic fields. Actually, critical current density even decreases by reducing grain size, which depends on the superconductivity of GBs. The findings in the paper provide theoretical foundations to achieve further improvement of Nb₃Sn with optimizing the flux pinning.

中文翻译：

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通过优化晶界钉扎势和晶粒尺寸提高 Nb3Sn 的临界电流密度

Nb ₃ Sn 超导体对于构建超出 NbTi 极限的高场磁体的应用具有重要意义。然而，其临界电流密度在高磁场下迅速下降（ > _{12 T)和Nb 3} Sn超导体的最先进水平仍不能满足规划的未来加速器磁体的要求。_{Nb 3} Sn 线材的主要磁通钉扎中心主要来自晶界 (GB)。在本文中，我们通过时间相关的 Ginzburg-Landau 理论和图形处理单元并行技术，从理论上研究了大规模多晶 Nb 3 中的涡钉扎和临界电流_密度通过在各种磁场下改变 GB 的钉扎电势和晶粒尺寸来实现 Sn 超导体。与传统的点状钉扎系统不同，通过抑制 GB 的超导性，发现临界电流不是单调函数。GB 的最大临界电流密度的最佳钉扎电位在很大程度上取决于磁场。此外，我们发现通过在低磁场下减小晶粒尺寸可以显着提高临界电流密度，而在高磁场下并不总是观察到临界电流密度的增加。实际上，临界电流密度甚至会随着晶粒尺寸的减小而降低，这取决于 GBs 的超导性。该论文的研究结果为实现Nb _{3的进一步改进提供了理论基础。}Sn 优化磁通钉扎。