Rapid and simple measurement of critical current density in HTS thin films using a permanent magnet method

Plasma and Fusion Research

Itoh

et al. 2011

Possibility of the accuracy improvement in the permanent magnet method for measuring the critical current density of a high-temperature superconducting (HTS) thin film has been investigated numerically. To this end, a numerical code has been developed for analyzing the shielding current density in an HTS sample. By using the code, the permanent magnet method has been reproduced numerically. The results of computations show that, by using the magnet strength B F as large as possible, the high accuracy can be assured with little effort. Furthermore, in order to improve the measurement accuracy of the critical current density near the film edge, it is necessary to use the magnet with the smallest radius.

Section: Numerical Resultsmentioning

confidence: 99%

“…As a novel noncontact method for measuring j C , Ohshima et al proposed the permanent magnet method for measuring the critical current density j C in a HTS thin film [2,3]. While moving a permanent magnet placed above an HTS thin film, they measure an electromagnetic force acting on the film.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation on Accuracy Improvement of Permanent Magnet Method for Measuring jC in High-Temperature Superconducting Film

Plasma and Fusion Research

Itoh

et al. 2011

“…Ohshima et al proposed another contactless method for measuring j C [4,5]. In the method, while moving a permanent magnet above an HTS film, the electromagnetic force acting on the film is measured.…”

Section: Introductionmentioning

confidence: 99%

High-speed method for analyzing shielding current density in HTS with cracks: implementation of <i>H</i>-matrix method to GMRES

Saitoh

2016

JASSE

Abstract. A high-speed analysis of a shielding current density in a high-temperature superconducting film containing cracks has been proposed. To this end, a numerical code has been developed for analyzing the shielding current density in an HTS film. In the code, the GMRES(k) with the H-matrix method has been implemented to solve a linear-system obtained by discretizing an initial-boundary-value problem of a nonlinear integro-differential equation with respect to time and space. The results of the computations show that, if the Jacobi scaling is not applied to the linear-system, the Newton method does not converge at a certain time step. Therefore, the Jacobi scaling is an necessary tool for analyzing the shielding current density. Furthermore, by using the GMRES(k) method with the H-matrix method as a linear-system solver, the time evolution of the shielding current can be analyzed with high speed. In conclusion, the speed of the GMRES(k) with H-matrix method is about 221.3 times as fast as that of the LU decomposition.

“…They conclude that can be evaluated from the threshold current. On the other hand, Ohshima et al have proposed the permanent magnet method [7], [8]. While moving a permanent magnet above an HTS film, the electromagnetic force acting on the film is measured.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Conventional/Enhanced Permanent Magnet Method: Influence of Crack on Accuracy

Saitoh

IEEE Trans. Appl. Supercond.

2012

The conventional and enhanced permanent magnet methods for measuring the critical current density in a high-temperature superconducting (HTS) tape have been simulated numerically. Moreover, the influence of the crack on the accuracy of the conventional method has been investigated. In order to simulate both permanent magnet methods, two types of numerical code have been developed for analysing the time evolution of a shielding current density in an HTS tape. The results of computations for the conventional method show that the maximum repulsive force acting on the tape drastically decreases when the symmetric axis of the magnet approaches the crack. On the other hand, the results of computations for the enhanced method show that the electromagnetic force near the center of the tape is roughly proportional to the critical current density. It is also found that the accuracy of the enhanced method compared with the conventional one hardly changes except for near the tape edge. Therefore, the enhanced method is a speedy and efficient method for measuring the spatial distribution of the critical current density.