Yoshida, Kiyoshi; Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Kamiya, Koji; Obana, Tetsuhiro*; Takahata, Kazuya*; Peyrot, M.*; Barabaschi, P.*
Physica C, 470(20), p.1727 - 1733, 2010/11
The upgrade of JT-60U magnet system to superconducting coils (JT-60SA) is carried out by both parties of Japanese government and European commission (EU) in the framework of the Broader Approach (BA) agreement. The magnet system for JT-60SA consists of 18 Toroidal Field (TF) coils, a Central Solenoid (CS) with four modules, six Equilibrium Field (EF) coils. The TF coil case encloses the winding pack and is the main structural component of the magnet system. The CS consists of four independent winding pack modules, which is support from the bottom of the TF coils. The six EF coils are attached to the TF coil cases through supports with flexible plates allowing radial displacements. The construction of CS and EF coils was started in 2008 in Japan. The construction of TF coils was started in 2009 in EU. This paper introduces the design of JT-60SA superconducting magnet and the design and experimental activities in Japan.
Nakamura, Hiroki; Machida, Masahiko; Koyama, Tomio*; Hamada, Noriaki*
Physica C, 470(20), p.1066 - 1069, 2010/11
Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*; Matsumoto, Hideki*
Physica C, 470(20), p.1137 - 1140, 2010/11
We construct a theory for Josephson junctions with multiple tunneling channels. We focus on two situations, i.e., a heterotic junction composed of two-gap-superconductor, insulator, and one-gap-superconductor, and a grain-boundary junction formed by two identical multi-gap superconductors. Then, we show that the magnetic field distribution of the Josephson vortex for s-wave superconductivity is more enlarged than that for s-wave without sign change between the order parameters. We display such anomalous vortices and suggest how to evaluate the enlargement.
Nakai, Noriyuki; Machida, Masahiko
Physica C, 470(20), p.1148 - 1150, 2010/11
Machida, Masahiko; Nakamura, Hiroki
Physica C, 470(20), p.1002 - 1006, 2010/11
Nakajima, Yasuyuki*; Tsuchiya, Yuji*; Taen, Toshihiro*; Yagyuda, Hidenori*; Tamegai, Tsuyoshi*; Okayasu, Satoru; Sasase, Masato*; Kitamura, Hisashi*; Murakami, Takeshi*
Physica C, 470(20), p.1103 - 1105, 2010/11
We report the formation of columnar defects in Co-doped BaFeAs single crystals with different heavy ion irradiations. The formation of columnar defects by 200 MeV Au ion irradiation is confirmed by transmission electron microscopy and their density is about 40% of the irradiation dose. Magneto-optical imaging and bulk magnetization measurements reveal that the critical current density is enhanced in the 200 MeV Au and 800 MeV Xe ion irradiated samples while is unchanged in the 200 MeV Ni ion irradiated sample. We also find that vortex creep rates are strongly suppressed by the columnar defects. We compare the effect of heavy-ion irradiation into Co-doped BaFeAs and cuprate superconductors.
Ishikado, Motoyuki; Shamoto, Shinichi; Kito, Hijiri*; Iyo, Akira*; Eisaki, Hiroshi*
no journal, ,
We successfully synthesized pure LaFeAsO1-xFx polycrtstalline sample 0 x 0.2 with almost no impurity. Especially, in high Fluorine concentration region that is no well studied so far, superconductivity suppresses(Tc 7K). Furthermore, we measured actual Fluorine content by SIMS (Secondary Ionization Mass Spectroscopy) method, and make phase diagram for actual Fluorine content vs. Tc, and we report about the detail.