Enhancement of current density in superconducting fusion magnets by a copper-clad stainless-steel conduit

1.热点温度是导管内电缆设计的重要指标之一。通常，束中作为稳定剂的铜的量由允许的热点温度确定，这与导体中具有高电流密度相矛盾。在这项研究中，提出了一种导体与铜包覆导管。束和铜包层之间的电流共享可以在失超期间减小束中的电流。这降低了热点温度。2.为了评估淬火电缆导管导体中的温升，我们使用两种实验技术测量了束和导管之间的接触热导。首先，将电流施加到冷却到液氮温度的短导体。由管束和导管之间的温差在温度上升过程中获得的电导，几乎与温度无关。在第二个实验中，在室温下在表面压力下测量电导。结果表明，表面压力对电导率有很大的影响。环境气体电导率的影响相对较小。从这些结果中，我们得出结论，它是必要的，以测量电导下的表面压力相当于预期的电磁力。因此，在设计阶段很难估算接触热导。3.采用零维热平衡方程，对模拟导体进行了铜包层效应分析。模拟导体具有直径为50 mm的圆形横截面，不锈钢导管外部有1 mm厚的铜包层。分析表明，即使管束和导管之间存在高热阻，也有可能降低热点温度。

1.The hotspot temperature is one of the most important design criteria for cable-in-conduit conductors. In general, the amount of copper, as a stabilizer, in a bundle is determined by the allowable hotspot temperature, which contradicts to have a high current density in the conductor. In this study, a conductor with a copper-clad conduit is proposed. Current sharing between the bundle and copper cladding can reduce the current in the bundle during a quench. This reduces the hotspot temperature.2.To evaluate temperature rise in a quenching cable-in-conduit conductor, we measured the thermal contact conductance between the bundle and the conduit using two experimental techniques. First, a current was applied to a short conductor cooled to liquid nitrogen temperature. The conductance, obtained from the temperature difference between the bundle and the conduit during temperature rise, was nearly independent of temperature. In the second experiments, conductance was measured under surface pressure at room temperature. The results confirmed that the conductance is strongly affected by the surface pressure. The effect of the conductivity of ambient gas was relatively small. From these results, we conclude that it is necessary to measure the conductance under a surface pressure equivalent to the expected electromagnetic force. The estimation of the thermal contact conductance is therefore considered difficult at the design phase.3.The effect of copper cladding was analyzed for simulated conductors using zero-dimensional heat-balance equations. The simulated conductors have a circular cross-section with a diameter of 50 mm and a 1-mm-thick copper cladding outside a stainless-steel conduit. The analyses demonstrated the possibility of reducing the hotspot temperature even though high thermal resistance exists between the bundle and conduit.