Study on new superconducting magnet structure for fusion device applying high specific heat of supercritical helium

提出了一种使用高比热超临界氦的电缆管道超导体的新结构，并对其可用性和潜力进行了讨论。结果表明：(1)由于超临界氦具有较大的热容，当出现交流损耗或涡流干扰时，使用超临界氦可以将温升降低到几十℃以上。(2)当氦气体形成循环时，氦压力在临界压力下并不恒定，因为压降是由流动摩擦引起的。因此，必须采用静电超临界氦作为热电容器。(3)对于像核加热这样的恒定热产生，必须准备独立于热电容器的氦气回路，以消除持续加热，防止温升。考虑发热密度，可以设计独立循环。(4)均流不平衡备用线圈的电流饱和是局部发热，对线圈稳定性有显著影响。在线圈励磁过程中产生热量约为100秒，是一种准稳态的热负荷。(5)利用磁通流动阻力和股电流饱和的情况在临界氦中进行了稳定性试验。(6)研究了超临界氦对磁通流动阻力的热容量，结果表明，超临界氦的热容量比加压氦提高了一个数量级以上。(7)由于沸腾潜热的存在，在液氦中获得了更高的容量。然而，导体周围的气泡会降低冷却能力。因此，没有相变的超临界氦将是有利的。

The new structure of a cable-in-conduit superconductor applying supercritical helium with high specific heat was proposed and the usability and the potential were discussed. The following results were obtained.(1) Since the supercritical helium has a large heat capacity, it is possible to reduce the temperature rise at one over several tens using the supercritical helium when the AC losses or hearing by eddy current occurs.(2) When the circulation of helium gas is formed, the helium pressure does not keep constant at the critical pressure, for the pressure drop is caused by the flow friction. Therefore, the static supercritical helium must be applied as a heat capacitor. (3) For the constant heat generation such as nuclear heating, the independent helium circuit from the heat capacitor must be prepared to remove the continuous heating and to prevent from temperature rise. The independent circulation is able to be designed considering the heat generation density.(4) The current saturation in a stand by imbalanced current sharing, which is local heat generation, affects on the stability of the coil remarkably. The heat generation occurs during the coil excitation with about 100 seconds and is a quasi-steady heat load.(5) The stability test was able to be carried out in the critical helium under the heat load by flux-flow resistance and the situation of the strand current saturation.(6) The heat capacity of the supercritical helium to the flux-flow resistance was investigated and it was clarified that the capacity was improved over one order of magnitude than of pressurized helium.(7) The higher capacity is obtained in liquid helium, for the latent heat at boiling is available. However, the cooling ability will be reduced by the bubbles surrounding the conductor. So, the supercritical helium which does not have phase transition will be profitable.