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

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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.