Thermal-Engineering Stucy on Early Detection of Quench and Hyper Stabilization Method of Superconducting Coil

本课题旨在阐明强制冷却和浸没冷却超导线圈中淬火的热机理，建立超导线圈的热稳定性理论，并提出早期检测淬火的方法。在这个为期3年的研究项目中获得的结果概要如下。对强制冷却和浸没冷却超导线圈的淬火机理和热稳定性进行了数值分析。定量地阐明了各种控制因素对其的影响，建立了淬火早期预测的基本概念。由于淬火现象是极快的瞬态和不确定的，并且它发生在很强的磁场中，因此几乎不可能预测其发生的时间和地点。因此，我们提出了两种新的检测方法：一种是薄膜热传感器，另一种是可视化技术。通过液氦中脉冲加热带材快速瞬态沸腾换热实验，验证了薄膜式热传感器的实用性。实验所得的数据对热稳定性的精确分析也是必要的。试件为20 μ m厚的不锈钢带，其表面均涂有PVF膜和碳糊膜。这种条带结构是为了模拟实际使用中的绝缘超导体，碳糊膜则是电阻温度计的一部分。考虑涂层的热容量和瞬态温度分布，通过数值计算对实验原始值进行了简化，得到的传热数据具有满意的精度，可以将薄膜传感器应用于淬火起爆的早期检测。利用浸入液氦的薄饼型超导线圈，研究了淬火及其快速传播的可视化技术。结果表明，可视化技术是一种很有前途的早期检测淬火的工具；然而，要将这种迷人的技术应用到实际的超导线圈中，还需要进一步的研究。少

The aim of this research project is to clarify thermal mechanism of quench in forced-and immersion-cooled superconducting coils, and to establish theory of thermal stability of superconducting coil, and to propose methods for early detection of the quench. The outline of the results obtained in this 3-year research project is given below.1. Numerical analyzes of quench mechanism and thermal stability of forced-and immersion-cooled superconducting coils were carried out. Various influences of governing factors on them were clarified quantitatively and the basic concept of early prediction of quench was established.2. Since the quench phenomenon is extremely rapid transient and indeterminate, and it occurs in a very strong magnetic field, it is almost impossible to predict the time and place of its occurrence. hence we propose two novel detecting methods : one is a film thermal sensor, and another is a visualization technique.Practical applicability of the film thermal sensor was examine … More d in an experiment on rapid transient boiling heat transfer of a pulse-heated strip in liquid helium. The data obtained in the experiment are also necessary for the precise analysis of the thermal stability. The test piece was a 20-mum-thick stainless steel strip, both surface of which were coated with PVF film and a carbon-paste film. This strip structure was to simulate an insulated superconductor in practical use and the carbon-paste film performed the part of an electric resistance thermometer. The heat-transfer data were reduced from the experimental raw values by numerical calculation considering the heat capacity and transient temperature distribution of the coating layrs : the obtained results had satisfactory accuracy to apply the film sensor to the early detection of quench initiation.As for a visualization technique of quench and its rapid propagation was investigated using a pancake-type superconducting coil immesed in liquid helium. It was found that the visualization technique will be a promising tool of the early detectin of quench ; however, we need further research to make applicatin of this charming technique to practical superconducting coils. Less