| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Hiroaki National Institute for Fusion Science, Theory and Computer Simulation Center, Research Associate, 理論シミュレーション研究センター, 助手 (30311210)
YUASA Tetsuya Yamagata University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (30240146)
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| Research Abstract |
The magnetic shielding performance of the high-Tc superconductor (HTS) has been investigated numerically. In order to reproduce the crystallographic anisotropy in the critical current density of the MPMG-YBCO superconductor, the multiple-thin-layer approximation is assumed. Under the assumption, the behavior of the shielding current density is described by the integral-differential equation and the J-E constitutive relation. As the relation, the flux-flow and flux-creep model is adopted. Futhermore, the Kim model and the Bardeen-Stephan model are employed for the description of the B-dependence of the critical current density J_C and the flow resistivity ρ_f.
When discretized by means of the FEM and the θ-method, the initial-boundary-value problem of the governing equation is reduced to the nonlinear system G(s)=0. As the method for solving the system, the successive substitution method and the deaccelerated Newton method (DNM) have been employed. However, once the B-dependence of J_C and ρ_f is taken into account, it costs much CPU time to obtain the converged solutions. This is because the time step size and the relaxation factor must be taken so small to ensure the convergence. In order to overcome these difficulties, the DNM is modified so that the residual norm may decrease monotonously with respect to the iteration number. As a result, the total iteration number of the modified method is 1/230〜1/6 times as much as that of the DNM.
A numerical code for analyzing the time evolution of the shielding current density has been developed by use of the modified method and, by use of the code, the magnetic shielding performance of the HIS plate is investigated. From the results of computations, it turns out that the HTS plate has a shielding ability against high-frequency magnetic fields even if it remains in a mixed state.
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