Background

Vortex stability is critically important for applications of type-II superconductors. If some vortices are detached from their pinning sites by external perturbations, the concomitant Joule heat will facilitate further motion of other vortices. This is a positive feedback process, which leads to a flux avalanche in the superconductor. So far, the existing research has not addressed the problem of the power threshold value (PVT) for activating a flux avalanche.

Objective

The primary objective is to study the influences of temperatures, applied magnetic fields and laser activating sites on the PTV of YBa₂Cu₃O_7-x (YBCO) thin films, and to find the relationship between avalanche velocities and laser activating sites.

Methods

We constructed two systems including the classical and high speed magneto-optical imaging (MOI) system. Both systems include two optical branches: one serves as an illuminating system, and the other is used to trigger the dendritic flux avalanche in superconducting film. The PTV was obtained by the classical MOI system while avalanche velocities were acquired via the high speed MOI system.

Results

The PTVs were experimentally obtained at different given temperatures, applied magnetic fields and activating sites, as well as the dependence of avalanche velocity on activating sites. Theoretically, two models are provided to depict the dependence of PTV on temperature and avalanche velocity on activating sites, respectively. The calculated results according to the present models are in reasonable agreement with the experiments.

Conclusions

The experimental results and constructed theoretical models help us to understand the characteristics of flux avalanche in YBCO films and are of significance to evaluate the flux stability for practical applications of high temperature superconducting films.

中文翻译：

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激光脉冲触发的YBa 2 Cu 3 O 7-x薄膜中涡流雪崩功率阈值的直接确定

背景

涡旋稳定性对于II型超导体的应用至关重要。如果某些涡旋由于外部扰动而从其固定位置脱离，则伴随的焦耳热将有助于其他涡旋的进一步运动。这是一个正反馈过程，导致超导体中发生磁通雪崩。迄今为止，现有研究尚未解决用于激活通量雪崩的功率阈值（PVT）的问题。

客观的

主要目的是研究温度，施加的磁场和激光激活部位对YBa ₂ Cu ₃ O _7-x（YBCO）薄膜的PTV的影响，并找出雪崩速度与激光激活部位之间的关系。

方法

我们构建了两个系统，包括经典和高速磁光成像（MOI）系统。两种系统都包括两个光学分支：一个作为照明系统，另一个用于触发超导膜中的树突通量雪崩。PTV是通过经典MOI系统获得的，而雪崩速度是通过高速MOI系统获得的。

结果

PTV是在不同的给定温度，施加的磁场和活化位点以及雪崩速度对活化位点的依赖性下通过实验获得的。从理论上讲，提供了两个模型来分别描述PTV对激活位点的温度和雪崩速度的依赖性。根据本模型计算的结果与实验结果基本吻合。

结论

实验结果和建立的理论模型有助于我们理解YBCO薄膜中的助焊剂雪崩特性，对于评估高温超导膜的实际应用中的助焊剂稳定性具有重要意义。