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Y. Takahashi,
T. Isono,
K. Hamada, Y. Nunoya,
Y. Nabara,
K. Matsui,
T. Hemmi,
K. Kawano,
N. Koizumi,
M. Oshikiri,
Y. Uno,
F. Tsutsumi,
M. Yoshikawa,
H. Nakajima,
K. Okuno,
A. Devred,
N. Mitchell
[show abstract]
[hide abstract]
ABSTRACT: The design and manufacture of Nb3Sn conductors for ITER toroidal field (TF) coils have many technical challenges. Although it was demonstrated in the ITER model coil project that the conductors have a sufficiently high performance and the engineering design is valid, unexpected issues arose. Through both theoretical and experimental efforts improved conductors were developed. The Japan Atomic Energy Agency started to procure improved conductors for TF coils as part of the ITER project. Because the required tonnage of Nb3Sn strands is quite large compared with past experience and the required superconducting performance is higher than that of the model coils, quality control techniques are very important for the successful manufacture of the strands. Approximately 60 ton of Nb3Sn strands have been successfully completed under a severe quality control regimen and all strands meet ITER specifications. This paper summarizes the technical developments leading to the first successful mass production of ITER TF conductors.
Nuclear Fusion 10/2011; 51(11):113015. · 4.09 Impact Factor
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Y. Nunoya,
Y. Nabara,
M. Yoshikawa,
K. Matsui,
T. Hemmi,
Y. Takahashi,
T. Isono,
N. Koizumi,
H. Nakajima,
B. Stepanov,
P. Bruzzone
[show abstract]
[hide abstract]
ABSTRACT: The Japan Atomic Energy Agency (JAEA) developed ITER TF Nb<sub>3</sub>Sn conductors that fulfill ITER requirements and has commenced fabricating the conductors to be used in the ITER TF coils. As a qualification of conductor fabrication, two full-size conductor samples, named as JATF4, were prepared and tested by the SULTAN facility at CRPP in Switzerland. Temperature sensors and voltage taps were attached on the three meter-long conductor samples to measure the current sharing temperature (Tcs). Measurements were performed at the beginning of the testing campaign, during cyclic test, and at the end of the campaign following a warm up and cool down. The Tcs values electrically assessed by the agreed procedure at outer magnetic fields of 10.78 T initially were 6.5 K and 6.2 K, and then 6.1 K and 6.0 K at the end of the campaign for each conductor, respectively. These results demonstrate that the conductors have a sufficient Tcs margin to satisfy the ITER TF conductor criterion of 5.7 K, and conductor fabrication is qualified. Details of the test results are presented and discussed.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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T. Hemmi,
S. Harjo,
T. Ito,
K. Matsui, Y. Nunoya,
N. Koizumi,
Y. Takahashi,
H. Nakajima,
K. Aizawa,
H. Suzuki,
S. Machiya,
H. Oguro,
Y. Tsuchiya,
K. Osamura
[show abstract]
[hide abstract]
ABSTRACT: The superconducting properties of Nb<sub>3</sub>Sn strands are very sensitive to strain. Measuring internal strain of Nb<sub>3</sub>Sn in Cable-In-Conduit Conductors (CICC) is important for evaluating the superconducting performance of CICC. Internal strain can be determined by neutron diffraction measurement using Takumi of J-PARC. Neutron diffraction measurement becomes a strong tool for evaluating directly the internal strain of Nb<sub>3</sub>Sn in CICC.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Japan Atomic Energy Agency has developed Nb3Sn strands for the ITER magnet, whose critical current density is about 1.4 times as large as that of ITER CS Model Coil. The magnetic field, temperature, and strain dependence on the critical current (Ic) of the strands were measured with apparatus that were developed by the authors. The strain properties in particular were investigated in detail, with strain tensor analysis revealing that the upper critical field dependence on strain can be naturally formulated using a high order polynomial terms of strain taking into account residual strain due to thermal contraction difference inside the strand and strain applied externally. A correlation formula for field, temperature, strain and Ic of the strand is discussed and presented. Recent results of fabricating strands for ITER TF coil are then finally provided.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
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K. Matsui,
T. Isono, Y. Nunoya,
T. Hemmi,
Y. Okui,
M. Oshikiri,
N. Koizumi,
Y. Takahashi,
K. Okuno,
B. Stepanov,
P. Bruzzone
[show abstract]
[hide abstract]
ABSTRACT: Many full size conductors for the ITER TF coils have been tested at the SULTAN test facility in Switzerland for conductor qualification. JAEA tested two samples and two kinds of Nb<sub>3</sub>Sn strands were evaluated through the tests. Now another sample named JATF3 has been tested, which uses two other kinds of Nb<sub>3</sub>Sn strands. The strands satisfy the critical current density J<sub>c</sub> requirement, but results of the conductor test were lower than our expectation. After the test, JAEA has been investigating the reason by X-ray CT scan and destructive inspection, and has found a possible reason.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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D. Bessette,
L. Bottura,
A. Devred,
N. Mitchell,
K. Okuno, Y. Nunoya,
C. Sborchia,
Y. Takahashi,
A. Verweij,
A. Vostner,
R. Zanino,
E. Zapretilina
[show abstract]
[hide abstract]
ABSTRACT: In this paper we report the main test results obtained on the Poloidal Field Conductor Insert coil (PFI) for the International Thermonuclear Experimental Reactor (ITER), built jointly by the EU and RF ITER parties, recently installed and tested in the CS Model Coil facility, at JAEA-Naka. During the test we (a) verified the DC and AC operating margin of the NbTi Cable-in-Conduit Conductor in conditions representative of the operation of the ITER PF coils, (b) measured the intermediate conductor joint resistance, margin and loss, and (c) measured the AC loss of the conductor and its changes once subjected to a significant number of Lorentz force cycles. We compare the results obtained to expectations from strand and cable characterization, which were studied extensively earlier. We finally discuss the implications for the ITER PF system.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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T. Hemmi,
N. Koizumi, Y. Nunoya,
Y. Okui,
K. Matsui,
Y. Nabara,
T. Isono,
Y. Takahashi,
K. Okuno,
N. Banno,
A. Kikuchi,
Y. Iijima,
T. Takeuchi
[show abstract]
[hide abstract]
ABSTRACT: A Nb<sub>3</sub>Al strand, produced by the ldquorapid-heating, quenching and transformation annealing (RHQT)rdquo process, has been developed in collaboration between JAEA and NIMS aiming at application to the conductor in a fusion DEMO reactor. A detailed description of critical current characteristics of the Nb<sub>3</sub>Al RHQT strand may assist in predicting accurate conductor performance. Calculations of the critical current density are adjusted to 5 scaling laws. Advantages of the newly developed strand compared to the Nb<sub>3</sub>Sn ITER strand and the Nb<sub>3</sub>Al Insert strand include improved strain tolerance and a higher current density at around 16 T. Performance parameters of the Nb<sub>3</sub>Al RHQT strand include 450 A/mm<sup>2</sup> at 15.9 T, 5.7 K and -0.4%. These performance parameters fulfill the requirements of the TF conductor of the fusion DEMO reactor. Therefore, the Nb<sub>3</sub>Al RHQT strand represents an improved performance with prospective application in the fusion DEMO reactor. In addition, the Nb<sub>3</sub>Al RHQT strand has the potential to enhance further the critical current density.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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Y. Nunoya,
Y. Takahashi,
K. Hamada,
T. Isono,
K. Matsui,
M. Oshikiri,
Y. Nabara,
T. Hemmi,
H. Nakajima,
K. Kawano,
F. Tsutsumi,
K. Takano,
Y. Uno,
N. Koizumi,
K. Okuno,
W. Baker,
E. Salpietro,
H. Rajainmaki,
C. Sborchia,
N. Mitchell
[show abstract]
[hide abstract]
ABSTRACT: ITER PFCI has been manufactured in the Europe and installed into the ITER Test Facility in Naka, Japan. The conductor is NbTi cable-in-conduit conductor with thick square stainless steel jacket and almost identical with the design of the ITER PF coils. The main objective of this test is the characterization of the conductor and joints at the conditions relevant to the ITER PF coil operation. Intermediate joint is located in the winding at relatively high field to examine its performance. The main items in the PFCI test program are thermo-hydraulic test, DC mode test, cyclic test and pulse mode test. The PFCI and CSMC were successfully cooled down to cryogenic temperature within 450 hours. The test of the PFCI was performed from May to August 2008. The key technology of the installation, the test methods and procedures, and some preliminary results of cool-down are described in this paper.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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Y. Takahashi,
T. Isono,
N. Koizumi, Y. Nunoya,
K. Matsui,
Y. Nabara,
T. Hemmi,
M. Oshikiri,
Y. Uno,
K. Okuno,
B. Stepanov,
P. Bruzzone
[show abstract]
[hide abstract]
ABSTRACT: The cable-in-conduit conductors for the ITER TF coils are fabricated using the latest high performance strands. The strands made by bronze and internal-tin methods are used for the conductors with a void fraction of 29% and 33%, respectively. Superconducting performance of the conductors was measured at the operating condition of the TF coils. The measured current sharing temperatures Tcs are 6.3-6.6 K for the bronze and 5.6-6.1 K for the internal-tin. The Tcs of the conductor with void fraction of 29% is 0.1-0.3 K higher than the conductor with a void fraction of 33%. It is shown from the results that the strain on the cable is between 0.7% and 0.75% and the n-values are between 4 and 6, much smaller than the n-values of strands.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Japan Atomic Energy Agency has developed four types of strand which can be used in the ITER TF coils. One is a strand made by an internal tin process strand and the others are bronze process strands. The achieved critical current density is more than 790 in the bronze process strands and more than 980 in the internal tin process strand under 4.2 K temperature and 12 T magnetic field and there is hysteresis loss of less than 770 mJ/cc under 3 T cycle. Since these strands are utilized with an external strain, it is necessary to evaluate strain dependency to confirm the ITER conductor design. An apparatus to measure the strain dependency was newly developed. It has a horseshoe-shaped ring to produce uniform axial compressive or tensile strain along the strand length, a strand being soldered on the outer surface of the ring. The detailed strand characteristics were investigated subjecting the developed strands to a magnetic field from 10 T to 13 T, a strain from about 0.8% to 0.5%, and a temperature from 4.2 K to the critical temperature. When the critical current is normalized to that under the conditions where strain is intrinsically zero, the bronze process strands exhibit better performance than the internal tin process strand. However, the three bronze process strands do not exhibit the same -strain characteristics. Two types of scaling relations are applied to the data, and good expressions of strand performance were obtained by the least square method within 3 A as RMS.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Coupling loss with long time constants has been found a troublesome phenomenon for large size magnet application of superconductor because it would not be simply estimated from AC loss measurement of short sample conductor. In order to investigate the mechanism of the loss, we measured trajectories of strands of sample CIC (3<sup>4</sup> = 81) conductor. The measured length is 1 m along the conductor axis. By analyzing those trajectories, two important facts are cleared. One is that contact periods between two strands are calculated by the function of twisting pitches, not always by the Least Common Multiplier of twisting pitches. The other is that contact probabilities of two strands at each contactable point of sub cables depend on the difference of rotation angles of sub cables. To confirm the validity of this method, we calculated lengths of coupling current loops within 1 m in length by using experimentally obtained contact probabilities. The results are in very good agreement with lengths obtained from experimental results of strand trajectories. Then we computed the loop length in the long conductor (<100 m), it was obtained that the average loop length would reached about 3 m.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: AC losses with long time constants can not be simply estimated from a short sample conductor because there are many irregular loops formed by strands strongly displaced from their original positions. In our previous work, we measured trajectories of 81 strands of NbTi conductor and it was proved that strongly displaced strands produced many line contacts with other strands, and thereby caused low contact resistance and long time constants. Long loops due to the displacement of strands should also produce large AC loss because the time constant of the loss is proportional to the inductance, i.e., the length of coupling current loops. In order to investigate the long loops in practical conductors, we developed a method to estimate the strand positions over the entire length. In this method, only one cross section of the conductor is required to calculate gravities of each sub-cable. The strand trajectories are obtained in a manner that the same order sub-cables rotate around the gravity to form one order higher sub-cable. The estimated trajectories are in good agreement with the measured ones, with errors of 1 mm.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Japan Atomic Energy Agency has successfully developed Nb<sub>3</sub>Sn strand which fulfills ITER requirements. Because Nb<sub>3</sub>Sn is very susceptible to external strain which reduces critical current, critical temperature, and critical field, it is necessary to evaluate strain dependency of these Nb<sub>3</sub>Sn strands to confirm an ITER conductor design. An apparatus to measure the strain dependency was newly developed. It has a horseshoe-shaped ring and a strand is soldered on its outer surface. This shape produces uniform axial compressive or tensile strain along strand length by expanding or closing the opening of the ring. Critical current can be measured by the apparatus under a magnetic field up to 15 T, a temperature range of 4.2 K to 15 K, and strains. The maximum allowable current is about 300 A. The details of the apparatus and results of strand characterization are presented.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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R. Zanino,
M. Astrov,
M. Bagnasco,
W. Baker,
F. Bellina,
D. Ciazynski,
S. Egorov,
K. Kim,
J.L. Kvitkovic,
B. Lacroix, [......],
M. Polak,
P.L. Ribani,
E. Salpietro,
L. Savoldi Richard,
C. Sborchia,
Y. Takahashi,
P. Weng,
R. Wesche,
L. Zani,
E. Zapretilina
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we discuss the predictive analysis performed in support of the test program of the International Thermonuclear Experimental Reactor (ITER) poloidal field conductor insert (PFCI). A subset of the test program items was considered, with particular emphasis on DC performance and AC losses. The results and implications of the comparison of selected predictions from different laboratories will be presented.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Abstract Many cases exist where material supporting superconducting magnets at liquid helium temperature (4.2 K) are subjected to repeated applications of thermal and electromagnetic stresses. Additionally, since welding cannot be avoided, it is highly desirable that the materials used for supporting superconducting magnets possess excellent strength and toughness in addition to superior mechanical properties after heat treatment. In the current research, an austenitic stainless steel was subjected to a sensitizing heat treatment whose effects, at 4.2 K, on the tensile and the fatigue crack growth properties were clarified. Tensile ductility of the sensitized material was markedly reduced to about one-half that of the solution treated material because of an intergranular form of fracturing in such material. Fatigue crack growth rate of the sensitized material was faster than that of the solution treated material because of the tendency for cracks to develop intergranularly.
Fatigue & Fracture of Engineering Materials & Structures 04/2007; 18(6):671 - 678. · 0.85 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: AC losses consist of both regular losses that are proportional to cable twisting pitch squared and irregular losses that could not be estimated from short conductor sample test results. It was explained from our previous works that irregular loops in conductor which are caused by asymmetric strand positions as a result of low void fraction of CIC conductor, produce the losses with long time constants up to several hundred seconds. The observed long time constant indicates that the typical loop length should be about LCM (Least Common Multiplier) of all sub-staged cable pitches, and that contact conditions between the two strands forming the loop should be line contact. In order to investigate the contact conditions in detail, we traced 81(=3times3times3times3) strands every 11 mm of CIC sample conductor with 1 m in length whose strands are NbTi/Cu without any surface coating. The measured traces of 81 strands show that asymmetric strand positions, in other words, large displacements of strands from their original positions due to compressing the conductor provide many line contacts. It is found that the averaged line contact length reaches about 10 mm that is three order of magnitude larger than the 10<sup>-2 </sup> mm of point contact length
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
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R. Hirose,
S. Hayashi,
S. Fukumizu,
Y. Muroo,
H. Miyata,
Y. Okui,
A. Itoki,
T. Kamikado,
O. Ozaki, Y. Nunoya,
K. Okuno
[show abstract]
[hide abstract]
ABSTRACT: Cryogen-free superconducting magnets are becoming popular due to their simple operation compared with the conventional liquid Helium cooled magnet. However, for higher fields such as those greater than 14 T, the cryogen-free magnet has not become popular yet, because it is difficult to design and manufacture since the critical current is markedly reduced at higher fields and higher temperatures. We have developed two types of 15 T cryogen-free superconducting magnets, which will be among the highest field magnets in operation as cryogen-free with a GM cryocooler. One magnet has a 52 mm room temperature bore with overall dimensions of 820 mm in diameter and 680 mm in height. This magnet is designed so as to be simple in both operation and installation. Therefore, the magnet is cooled with a single 1 W GM cryocooler. Also, all coils are connected in series and charged with a single power supply. The magnet was successfully charged up to 15 T in 30 minutes and then charged slowly to 16 T without quench. The other magnet has a 170 mm room temperature bore with overall dimensions of 980 mm in diameter and 1015 mm in height. This magnet is designed so as to be used with temperature controlled sample cryostats with an outer diameter of 168 mm. The magnet is cooled with four 1 W GM cryocoolers and charged with a single power supply. The magnet was successfully charged up to 15 T in 90 minutes. Both magnets will enable high magnetic field research or application with very easy operation
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The ITER model coil experiments have revealed that degradation of the critical current (I<sub>c</sub>) and n index occurred in large Nb <sub>3</sub>Sn CICC's and the larger the electromagnetic force, the larger was the degradation. However, such degradation was not observed in the Nb<sub>3</sub>Al CICC. The authors developed a new model, in which the degradation of the I<sub>c</sub> and n index of an individual strand was taken into account, to interpret these results. Analytical model corrected from experimental results of a single strand is used in this model to estimate the degradation of each strand. The calculation results are in good agreement with the CICCs' test results. In addition, it is indicated that in case of the Nb<sub>3</sub>Sn CICC, the normal transition occurs from the strands at low field side in CICC cross section, where transverse load due to the electromagnetic force is the largest, resulting in the significant degradation in the I<sub>c</sub> and the n index. In contrast, in the case of the Nb<sub>3</sub>Al CICC, the normal transition takes place from the strands at high field in the CICC cross section, where the transverse load is small, resulting in no degradation in the I<sub>c</sub> and the n index
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
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R. Zanino,
M. Bagnasco,
W. Baker,
F. Bellina,
P. Bruzzone,
A. della Corte,
Y. Ilyin,
N. Martovetsky,
N. Mitchell,
L. Muzzi, [......],
P.L. Ribani,
M. Ricci,
E. Salpietro,
L.S. Richard,
A. Shikov,
V. Sytnikov,
Y. Takahashi,
A. Taran,
G. Vedernikov,
E. Zapretilina
[show abstract]
[hide abstract]
ABSTRACT: As the test of the PFCI is foreseen in 2006 at JAERI Naka, Japan, it is essential to consider in detail the lessons learned from the short NbTi sample tests, as well as the issues left open after them, in order to develop a suitable test program of the PFCI aimed at bridging the extrapolation gap between measured strand and future PF coil performance. Here we consider in particular the following issues: 1) the actual possibility to quench the PFCI conductor in the T<sub>CS</sub> tests before quenching the intermediate joint, 2) the question of the so-called sudden or premature quench, based on SULTAN sample results, applying a recently developed multi-solid and multi-channel extension of the Mithrandir code to a short sample analysis; 3) the feasibility of the AC losses calorimetry in the PFCI
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The THELMA (Thermal-Hydraulic-ELectro-MAgnetic) code has been developed with the aim of simulating the main aspects of superconductors to be used in the coils of the International Thermonuclear Experimental Reactor (ITER). An application of the code is presented here, where THELMA is used to simulate a single strand by considering, as cable elements, groups of superconducting (SC) filaments and the corresponding portion of the resistive matrix. This approach is used to reproduce the voltage-current characteristic of a Nb<sub>3</sub>Sn bronze route strand when subject to a bending mechanical load. Attention is focused particularly on the effect of the applied mechanical load on the critical current, which is considered a relevant item in the explanation of the degradation of the coil performance observed in several ITER Model and Insert Coil experiments. The longitudinal strain of the SC filaments is calculated by means of a composite beam model of the strand, taking into account the nonlinear, temperature-dependent material characteristics of the components. The whole load history is simulated, computing first the thermal strain due to cool-down, and then the mechanical strain due to the bending at 4.2 K
IEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor
