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

提出了一种利用高比热的超临界氦的超导电缆的新结构，并讨论了其实用性和潜力。获得了以下结果。(1)由于超临界氦具有大的热容量，所以当发生AC损耗或由涡电流引起的听力时，可以使用超临界氦将温度升高降低到几十分之一。(2)当氦气形成环流时，由于流动摩擦引起的压降，氦气压力在临界压力处并不恒定。因此，静态超临界氦必须用作热电容器。(3)对于恒定的热量产生，如核加热，必须准备独立于热电容器的氦回路，以消除持续加热并防止温度上升。独立循环能够考虑到热生成密度而被设计。(4)备用不平衡均流中的电流饱和是一种局部发热现象，对线圈的稳定性有显著影响。发热发生在线圈励磁期间约100秒，是准稳态热负荷。(5)在临界氦气下，利用磁通流动阻力和股线电流饱和的情况进行热负荷下的稳定性试验。(6)研究了超临界氦对通量流阻的热容，发现其热容比加压氦提高了一个数量级以上。(7)在液氦中获得更高的容量，因为沸腾时的潜热是可用的。然而，冷却能力将被导体周围的气泡降低。因此，不发生相变的超临界氦将是一个有利可图的研究领域。

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.