| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2005: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
As is well known, the critical current density is one of the most important parameters for engineering applications of the high-temperature superconductor (HTS). In this sense, the nondestructive and noncontact method has been desired for measuring the critical current density of the HTS thin film.
Claassen et al. proposed the inductive method for measuring the critical current density in HTS thin films. While applying an ac current in a small coil placed just above a film, they monitored harmonics of the voltage induced in the coil. As a result, they showed that the third-harmonic voltage is detected if and only if amplitude of the coil current exceeds a certain limit. This result means that the critical current density can be estimated by measuring the threshold current.
On the other hand, Ohshima et al. have proposed the permanent magnet method that is widely different from the inductive method. While bringing a permanent magnet closer to a HTS thin film, they measured the electromagn
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etic force acting on the film. As a result, they found that the maximum repulsive force is approximately proportional to the critical current density. This tendency implies that the critical current density can be determined by measuring the electromagnetic interaction between the magnet and the HTS film.
In the present study, the numerical code has been developed for analyzing the time evolution of the shielding current density in the HTS thin film and, by use of the code, both the inductive method and the permanent magnet method have been reproduced numerically. Conclusions obtained in the present study are summarized as follows.
1)For the case where the critical current density is below 0.25 MA/cm^2, an accuracy of the inductive method is not more than 3%. Otherwise, its accuracy is remarkably degraded.
2)The numerical simulation of the permanent magnet method shows that the maximum repulsive force varies in approximate proportion to the critical current density. These numerical results agree qualitatively with the experimental ones by Ohshima et al. Less
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