K. Matsui

Japan Atomic Energy Agency, Muramatsu, Niigata, Japan

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Publications (102)103.9 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate the ITER TF joint performance, the joint test sample, which consists of two short TF conductors and has full size joint, shall be tested using NIFS test facility under the condition of current of 68 kA and external field of 2 T. For high accuracy, the issue of voltage difference between cable and jacket had been anticipated in the evaluation of joint resistance. If a voltage difference exist between them, it is difficult to measure real joint resistance using voltage taps on the jacket. Therefore, the author first calculated the position where voltage of cable and jacket become equipotential and then decided the voltage tap position where the influence of voltage drop could be avoided. Thus, a high accuracy measurement of joint resistance could be achieved and the joint resistance was accurately evaluated as around 1 nΩ, which is well below the ITER requirement of 3 nΩ.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-4. DOI:10.1109/TASC.2014.2365543 · 1.32 Impact Factor
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    ABSTRACT: The Japan Atomic Energy Agency is responsible for procuring all amounts of central solenoid (CS) conductors for International Thermonuclear Experimental Reactor, including CS jacket sections. The conductor is cable-in-conduit conductor with a central spiral. A total of 576 Nb3Sn strands and 288 copper strands are cabled around the central spiral and then wrapped with stainless steel tape whose thickness is 0.08 mm. The maximum operating current is 40 kA at magnetic field of 13 T. CS jacket section is circular in square type tube made of JK2LB, which is high manganese stainless steel with boron added. Unit length of jacket sections is 7 m, and 6400 sections will be manufactured and inspected. Outer/inner dimension and weight are 51.3/35.3 mm and around 100 kg, respectively. Since the CS conductor suffers 60000 cycles of high electromagnetic force in the lifetime, severe requirements were specified for jacket sections in terms of not only high mechanical performance at 4 K but also of the size of initial defects in the jacket section. The minimum allowable defect size is estimated to be 2 mm2 × 0.2 mm by linear elastic fracture mechanics. Eddy current test (ECT) and phased array ultrasonic test (PAUT) were developed for non-destructive examination. The defects on inner and outer surfaces can be detected by ECT. The defects inside the jacket section can be detected by PAUT. These technologies and the inspected results of more than 700 jacket sections are reported in this paper.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-4. DOI:10.1109/TASC.2014.2364632 · 1.32 Impact Factor
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    ABSTRACT: We describe herein the characteristics of a Nb3Sn cable inserted into a conduit (cable-in-conduit conductor) for the International Thermonuclear Experimental Reactor toroidal field (TF) coil and central solenoid (CS). During insertion, the pulling force almost linearly increases as a function of the length Ii of cable is inserted. The slope of these curves for the CS cables are approximately 74% that for the TF cable, although the mass per unit length of the CS cable is approximately 63% that of the TF cable. Thus, friction between the CS cable and the conduit is slightly greater than that between the TF cable and the conduit. The number Np of rotations at the cable point for the TF cable increases to 50 almost linearly versus Ii. For Ii <; 150 m, Np for the CS cables also increases almost linearly with a slightly greater slope than for the TF cable. However, the slope decreases, and Np becomes constant at 30 for Ii ) 600 m. During compaction, the number Nt of rotations at the tail of the TF cable, the 613-m-long CS cable, and the 918-m-long CS cable increases almost linearly versus compacted cable length to 23, 36, and 69, respectively. The X-ray transmission imaging of the CS conductor clarifies the distributions of the fifth-stage twist pitch of the cable (Ip) over the entire length of the conductor. These results are consistent with a geometric analysis based on Np and Nt. The results for Ip peak at the cable point; thus, a sample of the conductor should be taken from the point to investigate how Ip elongation affects conductor performance.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-5. DOI:10.1109/TASC.2014.2360562 · 1.32 Impact Factor
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    ABSTRACT: Under the International Thermonuclear Experimental Reactor (ITER) project, the Japan Atomic Energy Agency (JAEA) is procuring all of the Nb3Sn conductors for the Central Solenoid (CS). The CS consists of six vertically stacked modules. The height and outer diameter of the CS are approximately 13 m and 4 m, respectively. The CS has a circular live stage cable. All of approximately 43 km of Nb3Sn CS cables will be manufactured in Japan. Before mass-production start, the jacketed cable conductors should be tested in the SULTAN facility in Switzerland to confirm their superconducting performance. The original cabling design had relatively long twist pitches and is referred to as the normal twist pitch (NTP) conductor. The NTP conductor test results revealed decreasing the current sharing temperature (Tcs) with increasing number of electro-magnetic (EM) load cycles. Therefore, a short twist pitch (STP) design was proposed and the STP conductors were also tested. The STP conductor results showed that the Tcs is stable during EM cyclic load tests. Because the conductors with STP have a smaller void fraction in the cable area than those with NTP, a higher compaction ratio during cabling is required and the possibility of damage on strands increases. The STP cable technology was developed in collaboration among Japanese cabling suppliers and JAEA. Several key technologies will be described in this paper.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3). DOI:10.1109/TASC.2013.2287311 · 1.32 Impact Factor
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    ABSTRACT: The performance of tour Nb3Sn conductors for the ITER central solenoids was tested. The current sharing temperatures (T-cs) were measured over approximately 9000 electromagnetic cycles, including two or three thermal cycles between 4.2 K and room temperature. T-cs, increased and became almost constant through the cycling. The gradient of the electric field against the temperature gradually decreased against cycling. The degradations caused by the electromagnetic force of the short twist pitch conductors were smaller than that of the original twist pitch conductor. The ac losses of short twist pitch conductors were several times higher than that of original twist pitch conductor. The dents and the removals of the Cr plating on the strands, which were formed during cabling, decreased the electric resistance between strands, which may cause the observed high ac loss. Inspection of the cable showed neither a clear bias of cable in the cross-sectional surface nor distorted strands in the lateral face. The high rigidity of the short twist pitch cable could prevent these plastic deformations, caused by the Lorentz force.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3). DOI:10.1109/TASC.2013.2284193 · 1.32 Impact Factor
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    ABSTRACT: The optimization of the heat treatment of Nb3Sn conductors for toroidal field coils in ITER was attempted to improve the current sharing temperatures (T-CS). Using the strand, we chose the pattern at 570 degrees C for 250 h and 650 degrees C for 100 h as the best, which increased the critical current and maintained the residual resistivity ratio higher than 100. The behavior of the critical current of the strand vs. the magnetic field, temperature, and strain was also improved. This pattern was used on two conductors, and their performances were tested. T-CS was evaluated over 1000 electromagnetic cycles and one thermal cycle. A sharp T-CS occurred at 50 cycles. Then T-CS linearly. Although this tendency was similar to the conductors that were heat treated with the original pattern, the degradation rates were improved. The ac losses (Q) before cycling were approximately 10% lower than those of the original pattern. Q after cycling became almost equivalent between two patterns. The conductor was inspected after the test, which showed that the conductor under the high-magnetic-field zone had contracted by approximately 600 ppm during the test. Some clearly deformed strands were observed under the high-magnetic-field zone, which could degrade T-CS.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3). DOI:10.1109/TASC.2013.2286675 · 1.32 Impact Factor
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    ABSTRACT: The authors performed some trials on TF coil fabrication and started first TF coil fabrication. In the trial on radial plate (RP) fabrication, flatness of machined RP section satisfied the target flatness of 1 mm and laser welding technique for joining RP sections was developed. The RP manufacturing plan is revised based on these trial results and fitting method of heat-treated conductor, whose length changes by its heat treatment, is also decided in this plan. Fabrication of the RP materials for the first TF coil has been completed and they satisfied the requirements, such as yield strength of 900 MPa at 4K. Preparation and commissioning of the tooling are in progress.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-5. DOI:10.1109/TASC.2013.2294959 · 1.32 Impact Factor
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    ABSTRACT: To evaluate presences of performance degradation due to strand bending in Nb3Sn cables, methods for investigating strand bending in Nb3Sn cables were developed by JAEA and demonstrated for the He-inlets of the ITER toroidal field coils. Conductor elongation and residual strain during the reaction heat treatment were measured. In addition, high-resolution X-ray computerized tomography was used to visually search for strand bending in the Nb3Sn cable. As a result, no large strand bending was observed.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-4. DOI:10.1109/TASC.2013.2297685 · 1.32 Impact Factor
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    ABSTRACT: The insulation system of the ITER TF coils consists of multi-layer glass/polyimide tapes impregnated a cyanate-ester/epoxy resin. The ITER TF coils are required to withstand an irradiation of 10 MGy from gamma-ray and neutrons since the ITER TF coils is exposed by fast neutron (>0.1 MeV) of 10(22) n/m(2) during the ITER operation. Cyanate-ester/epoxy blended resins and bonded glass/polyimide tapes are developed as insulation materials to realize the required radiation-hardness for the insulation of the ITER TF coils. To evaluate the radiation-hardness of the developed insulation materials, the inter-laminar shear strength (ILSS) of glass-fiber reinforced plastics (GFRP) fabricated using developed insulation materials is measured as one of most important mechanical properties before/after the irradiation in a fission reactor of JRR-3M. As a result, it is demonstrated that the GFRPs using the developed insulation materials have a sufficient performance to apply for the ITER TF coil insulation.
    Joint Conference of the Transactions of the Cryogenic Engineering; 01/2014
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    ABSTRACT: The performance of two Nb3Sn conductors for the ITER central solenoids was tested. The current sharing temperatures (T-cs) were measured over 17 050 electromagnetic cycles, including four thermal cycles between 4.2 K and room temperature. T-cs declined almost linearly over the 10 000 rated electromagnetic cycles. T-cs was nearly constant for 70% of the rated electromagnetic cycles, which implies the existence of a fatigue limit in the conductors. For 85% of the rated cycles, a very sharp T-cs degradation of approximately 0.2 K occurred. Some type of large deformation of strands, such as buckling, may have caused this sharp degradation. The effective strain degraded linearly with the electromagnetic force on the cable. The gradient after 10 000 cycles was 1.5 times greater than that before cycling. After 10 000 cycles, the ac losses of both conductors considerably decreased to less than half of those before cycling. These ac losses before cycling were less than a fourth of those of toroidal field conductors. After the test campaign, destructive inspection of the conductor clarified that on average, the distribution of residual strain along the cable was almost uniform at -32 ppm. It was also clarified that some strands were visibly deformed under a high magnetic field, whereas strands under a low magnetic field did not appear to be deformed. The deformations of the central solenoid cable were larger and wavier in subcables than those observed in the toroidal field cable. This plastic deformation of the strands could be one of the major reasons for the T-cs degradation during cyclic operation.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3). DOI:10.1109/TASC.2013.2244159 · 1.32 Impact Factor
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    ABSTRACT: In March 2010, the Japan Atomic Energy Agency (JAEA) was the first to start the mass production of toroidal field (TF) conductors among the six parties who were procuring TF conductors in the International Thermonuclear Experimental Reactor project. The height and width of the TF coils are 14 m and 9 m, respectively. The conductor is a cable-in-conduit conductor with an operating current of 68 kA. A circular multistage superconducting cable is inserted into a circular stainless steel jacket with a thickness of 2 mm. A total of 900 Nb3Sn strands and 522 copper strands are cabled around the central spiral and then wrapped with stainless steel tape whose thickness is 0.1 mm. The superconducting cables are inserted into the jacket assembled using the automatic butt Tungsten Inert Gas welding technique. Cable insertion is one of the key technologies in the jacketing process because the gap between the inner surface of the jacket and the outer diameter of the superconducting cable is only 2 mm in diameter. It was observed that the cabling pitch of the destructive sample is longer than the original pitch at cabling. JAEA carried out the tensile tests of the cable and the measurement of the cable rotation during the insertion to investigate the cause of the elongation. The cause of elongation was clarified, and the results are described in this paper.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3). DOI:10.1109/TASC.2013.2239693 · 1.32 Impact Factor
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    ABSTRACT: The Japan Domestic Agency (JADA) for ITER will procure toroidal field (TF) coil structures and winding packs and assemble them into a final TF coil configuration. Because the manufacturing schedule of the TF coils is a critical path toward the first plasma of ITER, coil manufacturing must be successful and proceed on schedule. Therefore, risk assessment and management for its manufacturing are essential. JADA performed a risk assessment on the basis of past manufacturing experiences and a risk mitigation policy for ITER-TF coil manufacturing. The results show that risks can be mitigated to a level that we can assure sufficient quality of the TF coil by sound design, manufacturing, and quality management processes that are developed through R&D activities and the use of prototypes.
    Journal of Plasma and Fusion Research 03/2013; 8. DOI:10.1585/pfr.8.2405062
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    ABSTRACT: Japan Atomic Energy Agency (JAEA) was the first to start the mass production of the TF conductors (jacketing) in March 2010 among the 6 parties who are procuring TF conductors in the ITER project. A 760-m Cu dummy conductor was successfully fabricated prior to the manufacture of the actual Nb3Sn conductors. Suitable manufacturing techniques for the long TF conductors were established during fabrication of the dummy conductor. This paper summarizes the technical developments including a high-level quality assurance, leading to the first successful mass production of ITER TF conductor. Approximately 63 tons of Nb3Sn strands were manufactured by the two suppliers by August 2011. This amount corresponds to approximately 60% of the total contribution from Japan. Five sDP conductors (415 m) and six rDP conductors (760 m) to be used in the TF coils were completed as of February 2011. This amount corresponds to approximately 25% of the total contribution (rDP: 24, sDP: 9) from Japan. JAEA is manufacturing one conductor per month under a contract with two Japanese companies for strands, one company for cabling and one company for jacketing. This progress is a significant step in the construction of the ITER machine.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):48019-. DOI:10.1109/TASC.2011.2178053 · 1.32 Impact Factor
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    ABSTRACT: The authors performed one-third scale trials of the conductor winding, the heat treatment and the insulation/impregnation to demonstrate and optimize fabrication procedure of TF coil. In this trial, accuracy of conductor length measurement system was confirmed in the winding trial. The conductor elongation and winding deformation due to the heat treatment were evaluated in the heat treatment trial. And the procedure of insulation and impregnation was established through the insulation/impregnation trial, and the insulation condition was fixed.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):4203005-4203005. DOI:10.1109/TASC.2011.2178379 · 1.32 Impact Factor
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    ABSTRACT: A method for evaluating the critical current of conductors is discussed in the context of the relationship between the electric field of the conduit surface and the superconducting cable in CIC conductors used for nuclear fusion reactors. The potential detected by voltage taps located on the surface of the conduit is the average potential of strands that have contact with the virtual surface area of the cable. This area is defined in terms of contact resistance between the conduit and strands as well as conduit resistance. Considering that a strand is uniformly distributed in a conductor due to the cabling effect, it is possible to replace in calculations the distribution of the electric field of a strand along the length of the conductor with the distribution of a cross section of the conductor, a replacement which renders possible statistical approach. As a result, the voltage measured by a pair of voltage taps located along the length of the conductor can be expressed in terms of a general formula which establishes a relationship between the electric field of the conduit surface and the superconducting cable including statistic errors. Using this formula, the electric field of the cable and the consequent superconducting properties of the conductor may be estimated with an acceptable degree of accuracy. Assessment of the experimental results and performance of the ITER conductors are introduced with discussion of temperature measurement issue, and the validity of the formula is discussed.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):4803804-4803804. DOI:10.1109/TASC.2012.2188772 · 1.32 Impact Factor
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    ABSTRACT: Japan Atomic Energy Agency (JAEA) started sub- and full-scale trials to qualify and optimize manufacturing procedure of ITER TF coil from March 2009 under the contract with Toshiba. As major outcome of these trials, feasibility of high accuracy of winding, prediction of the conductor elongation due to heat treatment and radial plate manufacture is confirmed. Therefore, JAEA can mostly establish manufacturing plan for the TF coil and then, start the first TF coil procurement from 2013, following to full demonstration through manufacturing a dummy double-pancake in 2012.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):4200404-4200404. DOI:10.1109/TASC.2011.2176697 · 1.32 Impact Factor
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    ABSTRACT: The performances of six ${\rm Nb}_{3}{\rm Sn}$ conductors for the ITER Toroidal Field coils were tested. Four of them showed similar degradation rates of their current sharing temperatures $T_{cs}$ over 1,000 electromagnetic cycles. By contrast, two of them showed sharp $T_{cs}$ degradations at 50 cycles, after which their slopes became similar to those of the other four conductors. These two cables seemed to shrink under high magnetic fields during the first 50 cycles, which caused the sharp $T_{cs}$ degradation. This shrinkage might arise from a decline in cable rigidity due to, for example, the deformation of strands or the breakage of the ${\rm Nb}_{3}{\rm Sn}$ filaments. The four mass-produced conductors had roughly the same AC loss before cycling. After 1,000 cycles, the AC losses of all the conductors decreased markedly to less than half of those before cycling, and the values became approximately the same. After the test campaign, the destructive inspection of two of the conductors made it clear that the conductor had shrunk by about 520 ppm under the high magnetic field during the test. It was also clarified that some strands were visibly deformed under the high magnetic field, whereas those under the low magnetic field did not look distorted. This plastic deformation of the strands could be one of the major reasons for the $T_{cs}$ degradation with cyclic operation.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):48048-. DOI:10.1109/TASC.2011.2178990 · 1.32 Impact Factor
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    ABSTRACT: Japan Atomic Energy Agency (JAEA) has fabricated and tested the four conductor samples composed of high performance ${\rm Nb}_{3}{\rm Sn}$ strands manufactured by the bronze-route process for the ITER Central Solenoid (CS) conductor. The current sharing temperature (Tcs) electrically assessed at 45.1 K and 10.85 T along the cycling loading at 48.8 kA and 10.85 T initially were 6.0 K and 6.1 K, and then 5.3 K and 5.5 K after 6000 cycles for the first SULTAN sample named JACS01, respectively. As results of second SULTAN sample named JACS02, the Tcs values initially were 7.2 K and 6.8 K, and then 6.6 K and 6.1 K after 10000 cycles for each conductor, respectively. The Tcs degradation was not saturated at the end of the test campaign. From the destructive observation, the large bending at the low transverse loading side in the high field zone was observed. The strand buckling and accumulating by slipping between the cable and the jacket are considered.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):4803305-4803305. DOI:10.1109/TASC.2011.2178370 · 1.32 Impact Factor
  • TEION KOGAKU (Journal of the Cryogenic Society of Japan) 01/2012; 47(3):172-177. DOI:10.2221/jcsj.47.172
  • TEION KOGAKU (Journal of the Cryogenic Society of Japan) 01/2012; 47(3):160-165. DOI:10.2221/jcsj.47.160

Publication Stats

592 Citations
103.90 Total Impact Points

Institutions

  • 1998–2014
    • Japan Atomic Energy Agency
      • • Quantum Beam Science Directorate
      • • Nuclear Science and Engineering Directorate
      Muramatsu, Niigata, Japan
  • 2004
    • ITER
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2002
    • Seikei University
      Edo, Tōkyō, Japan
  • 2001
    • Tohoku University
      Miyagi, Japan