2005 Fiscal Year Final Research Report Summary
Investigation on Irregular AC Losses in Large Superconducting Coils
| Project/Area Number |
15360491
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear fusion studies
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| Research Institution | Tohoku University |
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Principal Investigator |
HAMAJIMA Takataro Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (00314815)
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| Co-Investigator(Kenkyū-buntansha) |
TSUDA Makoto Tohoku University, Graduate School of engineering, Associate Professor, 大学院・工学研究科, 助教授 (10267411)
YAGAI Tsuyoshi Tohoku University, Graduate School of engineering, Research Associate, 大学院・工学研究科, 助手 (60361127)
TAKAHATA Kazuya National Institute for Fusion Science, Department of Large Helical Device Project, Associate Professor, 大型ヘリカル研究部, 助教授 (10216773)
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| Project Period (FY) |
2003 – 2005
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| Keywords | AC loss / Irregular coupling loss / Cable in conduit conductor / Long time constant / Sub-cable / Displacement / Contact resistance / Strand locations |
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| Research Abstract |
It is found that irregular AC losses in cable-in-conduit superconductors cannot be estimated from short conductor sample test results. Current loops, which must be irregularly formed in the cable, decay with the long time constants, and hence enhance the AC losses.
We propose a mechanism forming the long loops. The cable is composed of several staged sub-cables. If one strand on the surface of a sub-cable contacts with the other strand on the surface of the adjacent sub-cable, the two strands should encounter each other again at LCM distance of all staged cable pitches, and thereby result in forming a pair of a long loop. The time constants of these loops are fundamentally described as ratios of their inductances to their contact resistances.
In order to estimate the time constants τ=L/R of the long LCM loops, we measured the cross contact resistance between the two strands in LHe. The test results showed that the cross contacting resistances were about 50 μΩ. The results suggest that the time constants are around 0.1 s, which is shorter than the measured time constants of 5 to 100 s. This stems from the fact that the cross contact area, which is estimated about 10 μm in the elastic limit, is very small compared with the line contact area, which is the order of cm.
In order to investigate the contact conditions in more detail, We fabricated a cable composed of 81 strands with 40% void fraction, and identified 3-dimensional locations of all strands in the cable. It is found that some loops have several line contacts with more than 10mm. This fact demonstrates that the loops with long time constants should be formed.
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Research Products
(12 results)
