Yingxu Li

Electromagnetic behaviors of superconducting Nb3Sn wire under a time-dependent current injection

We build a 3D model to analyze the electromagnetic behaviors of Nb3Sn filamentary strand exposed to a time-varying current injection, under the consideration of n value and strain effect. Electromagnetic behaviors, performance degradation and AC loss are investigated. Results show that the filament bundles prevent a further field penetration from the outer shell into the interior matrix. Different current/field profiles occur in the strand and outside. Compared to the critical current, the average transport current keeps a high value with little change over a broader strain range, and has a larger magnitude by several orders of magnitude. Increasing the strain results in a suppression of the current transport capacity, and part of the current is expelled into the metal matrix causing larger AC loss. The larger twist pitch implies a longer current circuit and more magnetic flux enclosed, thus increasing the loss. More details are presented in the paper.

Anisotropic critical-state model of type-II superconducting slabs

We introduce a critical-state model incorporating the anisotropy of flux-line pinning to analyze the critical states developing in an anisotropic biaxial superconducting slab exposed to a uniform perpendicular magnetic field and to two crossed in-plane magnetic fields which are applied successively. The theory is an extension of the anisotropic collective pinning theory developed by Mikitik and Brandt. The anisotropic flux-line pinning enters into the critical states by generating the angular dependence of the critical current density and by deviating the direction of the electric field from the current in the plane perpendicular to the vortex line. We find that an enhanced in-plane anisotropy moderates the gradients of the magnitudes of the magnetic field and the electric field along the slab thickness, however increases the gradients of their rotations.

COMPUTATIONAL METHOD FOR ELASTIC–PLASTIC AND ANISOTROPIC SUPERCONDUCTING CABLE UNDER SIMPLE LOAD

International Thermonuclear Experimental Reactor (ITER) Cable-in-conduit Conductor (CICC) presents a typical hierarchical twisted configuration. An unpredictable stress–strain distribution is generated in each-level subcable under experimental loading tests or realistic operating conditions. The mechanical response relates to the threshold of transport currents on CICC which indicates the performance and stability of ITER magnets. To quantitatively assess mechanical deformation we develop an analytical scheme based on the hierarchical approach in the classical wire rope theory, following a successive top-down algorithm from the highest cable level to the lowest. The determination and evaluation of complex contact occurrence among adjacent strands is a key aspect which is formulated via a friction–contact model. Finite element (FE) method is used to extend the analytical approach that treats only elastic and isotropic material to the anisotropy and plasticity. The results show that the interstrand friction acts as a moderation for the axial deformation, and the interaction among the conductors has a stronger impact on the cable deformation than that between the conductor and jacket. It is suggested that under tensile load, the displacement constraints at the end and the strand anisotropy help to reduce the cable longitudinal deformation. It is also recommended that increasing the subsequent pitch is beneficial to reducing the cable deformation level.