Visualization of local dissipation in superconducting tapes under the influence of external magnetic field and mechanical strain simulating practical operation conditions

(1)高场型低温扫描激光显微镜(HF-LTSLM)：我们首次成功地在高达5T的高外场下，以微米分辨率显示了超导带材中的局部耗散。(2)激光感应塞贝克电压成像：利用缺陷或倾斜颗粒处的非对称塞贝克常数，(3)扫描SQUID显微镜：采用高分辨率、高灵敏度的SQUID传感器和直径为10μm的拾取线圈相结合的磁力显微镜，研究了带材中捕获的涡旋和局部电流的动态变化。(4)扫描霍尔探针显微镜：通过研制一套以微霍尔探头为传感头的系统，实现了大电流、宽范围的磁显微镜。它揭示了当前的障碍和c…更多的电流分布在加工带中，如多丝结构。在与加工小组的紧密合作中，我们发现了不同类型的障碍，取决于加工组合，因此可以有效地改善工艺条件。在宽度为80μm的窄灯丝中，最大临界电流密度J_c达到5.2 mA/cm~2(I_c=413A/cm~(-w))。这与在单晶衬底上的数值相当。此外，还建立了一种方法来研究外加磁场下轴向机械应变对超导带中电流输运的影响。基于对局域电磁行为的洞察，我们还改进了我们的物理模型来描述全局电场-v。S。-电流密度特性作为温度、外场和应变的函数。这也使我们能够根据有限的测量集在广泛的操作条件下预测性能。较少

We have succeeded to developed several techniques which allow us to visualize local electromagnetic properties of superconducting tapes.(1) High field type low temperature scanning laser microscope (HF-LTSLM): We succeeded to visualize local dissipation in the tape with a micro-meter resolution for the first time under high external field up to 5 T.(2) Laser induced Seebeck Voltage Imaging: By use of asymmetric Seebeck constant at defect or tilted grain, we visualized defect position and grain structure in the coated conductors.(3) Scanning SQUID microscopy: Dynamics of the trapped vortices in the tape and local current flow have been investigated by high resolution and high sensitive magnetic microscopy using SQUID sensor coupled with a small pickup coil with a diameter of 10 μm.(4) Scanning Hall probe microscopy: High current and wide range magnetic microscopy has been achieved by developing a system using micro-Hall probe as a sensor head. It reveals current blocking obstacles and c … More urrent distribution in processed tapes such as multi-filamentary structures.In a tight collaboration with processing groups, we have found different types of obstacles depending on processing combination, and therefore could improve the process conditions effectively. Finally, the maximum critical current density, J_c, has reached to 5.2 MA/cm^2 (I_c=413 A/cm-w) even in narrow filament having 80 μm of width. This is comparable to the value on single crystalline substrate.Furthermore, a method has been established to investigate the influence of axial mechanical strain on current transport in the superconducting tape under external magnetic field. Based on the insights on the local electromagnetic behavior, we have also improved our physical model to describe global electric field-v. s.-current density characteristics as a function of temperature, external field and strain. This also allows us to predict the properties over broad operation conditions based on limited sets of measurements. Less