TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)

[title in Japanese]

Kaoru YAMAFUJI

1994 Volume 29 Issue 6 Pages 211
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.211

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Crystal Growth of Y Based Superconductors on Solidification Processing

Kenji FURUYA, Yuh SHIOHARA

1994 Volume 29 Issue 6 Pages 215-222
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.215

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As a result of improvement on melt/solidification processing, the critical current density (J_c) at 77K of YBCO bulk superconductors has been increased even in a magnetic field. Especially, QMG and MPMG method has become to give a J_c value high enough for practical use. Zonemelting method has been utilized to fabricate superconducting wires. Recently, a single crystal Y 123 has been also continuously fabricated by using a crystal pulling method. The growth mechanism of 123 crystal from the partial molten state is gradually clarified and the special peritectic reaction mechanism has been proposed. Applicable process (e.g. superconductiog wires, magnetic bearing) are expected to be developed.

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Specific Heat Measurement of Polyvinylformal and Carbon for a Thermometer in Low Temperature

Kazutoshi KAJI, Kenji TOCHIGI, Sadayuki OKADA, Kunishige KURODA

1994 Volume 29 Issue 6 Pages 223-228
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.223

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Specific heats of polyvinylformal, which is insulator for superconducting wires, and carbon for thermometers are measured in the temperature range from 14K to 248K for the former and ranges from 14K to 201K and from 243K to 274K for the latter by an adiabatic calorimeter. Experimental results are represented by 6th- or 7th-polynomial equations with respect to temperature. Specific heats of polyvinylformal above 20K and ones of carbon for thermometers above 50K are precise enough for numerical analysis of the thermal stability on a superconducting coils.

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Sub-Micron Filament Nb-Ti Superconducting Wires with Cu-Ni-Mn Alloy for AC Use

AC Loss

Katsumi MIYASHITA, Shuji SAKAI, Kunihisa KAMATA, Hiroki TANAKA

1994 Volume 29 Issue 6 Pages 229-237
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.229

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AC loss characteristics of sub-micron filament Nb-Ti superconducting wires with Cu-Ni-Mn alloy matrix for AC use are described. To investigate the relationship between the proximity effect and hysteresis loss, the Nb-Ti superconducting wires are prepared, 1) changing Ni (10 and 30wt%) and Mn (0-1.78wt%) contents in Cu-Ni-Mn alloy matrix, 2) the variation of ratio of filament spacing (d_n) to filament diameter (d_f). The addition of Mn to Cu-Ni matrix reduces the proximity effect by magnetic scattering and the allowed efficient Mn content to reduce hysteresis losses of Nb-Ti filaments is in the range of 0.9wt% to 1.78wt%. The relationships between d_n and hysteresis losses were investigated and the optimum d_n to reduce the proximity effect were d_n=0.2μm (Cu-10%Ni matrix), d_n=0.08μm (Cu-10%Ni-0.9%Mn), d_n=0.052μm (Cu-30%Ni-0.9%Mn) and d_n=0.048μm (Cu-30%Ni-1.34%Mn). Weak coupling due to the proximity effect has no influence on increasing hysteresis loss at an amplitude field of more than B_m=0.6-0.8T.

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Sub-Micron Filament Nb-Ti Superconducting Wires with Cu-Ni-Mn Alloy for AC Use

Critical Current Density and RRR of Stabilizer Cu

Katsumi MIYASHITA, Shuji SAKAI, Kunihisa KAMATA, Hiroki TANAKA

1994 Volume 29 Issue 6 Pages 238-244
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.238

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Critical current density and stability of sub-micron filament Nb-Ti superconducting wires with Cu-Ni-Mn alloy matrix are described. Characteristics of critical current density J_c depend on filament diameter d_f, kinds of matrix and ratio of filament spacing d_n to d_f. In the case of large d_n/d_f(=0.65-1) wires, increasing J_c with decreasing d_f is slight due to low pinning force. Residual Resistance Ratio (RRR) of the wires which were heat treated (100-250°C×1hour) at final size increased to 70-80. These values are three times those of the as drawn wires. The final heat treatment at more than 300°C degraded RRR and J_c, because of Ni diffusion. AC (50Hz) quench current at high field (>2T) of the secondary twisted cable with 36 strands (copper ratio 1.9) is higher than DC critical current of the secondary twisted cable.

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Critical Current Densities in the Artificial Pinning Structure Composed of Nb/NbTi Multilayers

Kaname MATSUMOTO, Hirokazu TAKEWAKI, Yasuzo TANAKA, Ohsuke MIURA, Kaor ...

1994 Volume 29 Issue 6 Pages 245-250
Published: June 25, 1994
Released on J-STAGE: February 26, 2010

DOIhttps://doi.org/10.2221/jcsj.29.245

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Superconducting properties in an artificially designed pin structure composed of Nb/NbTi multilayers in a NbTi superconducting wire are analyzed theoretically with the experimental results and it is found an aspect ratio of plate-like Nb artificial pins in the pin structure gives effect to the critical current density in the wire. This is useful parameter for obtaining more high critical current densities, since both the elementary pinning force and the pin density can be changed without reducing the pinning efficiency in the pin structure.

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