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

点击翻译按钮获取中文摘要

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