Stability Analysis And Research Of The Superconductors For CFETR Poloidal Field Magnets

China Fusion Engineering Testing Reactor (CFETR) is a new superconducting tokamak device designed by China independently, which has important significance for implementing the design and construction of commercial fusion reactors in the future. The main purpose of building CFETR is to fully fill the gap of science and technology between ITER and DEMO, and develop the key technology tests of fusion reactor. The poloidal field (PF) magnet is one of the core components of CFETR magnet system, which plays an important role in controlling the location and shape of the plasma. In order to insure the stable operation of the PF system and provide the basis for optimize the conductors of poloidal field, the detailed analysis and study around the stability related problems of PF magnets and conductors were performed.This article firstly performed the two-dimensional and three-dimensional electromagnetic analysis of CFETR magnet system, especially the PF coils in three different divertor equilibrium configurations by ANSYS. The distributions and values of the magnetic field and electromagnetic force for the magnet system of CFETR and each PF coil were obtained under the steady current condition of three different divertor configurations. The electromagnetic-structural coupling analysis of the PF magnets was carried out on the basis of the three-dimensional electromagnetic analysis. The distributions of the stress and displacement of each PF coil and its related components were obtained. The above results all meet the design requirements, and they also provide the necessary load data for the subsequent conductor stability analysis. Then, the analysis of the Cable-in-conduit conductors (CICC) for PF system was detailed studied by GANDALF program. For stability analysis, typical mechanical disturbance and electromagnetic disturbance are applied, respectively. The calculation of stability margin, minimum quench energy and temperature margin were presented in this paper. The rules of stability margin and current sharing temperature dependence of operating current and background field were discussed and the quench characteristics were studied.Moreover, CFETR magnet system works in the time-varying magnetic field, the AC loss of superconductor is an important factor which influences the stability of conductor. This paper calculated the AC loss of PF CICC under different external magnetic field rate of change and studied the impact of the twist pitch of conductor cable at each stage on AC loss. Finally, the stability of PF CICC was studied considering the effect of AC loss. The analysis results illustrate that the present design of CFETR PF conductor can sufficiently satisfy the requirement of safety margin.