研究成果論文
2014年
1：Rutherford Flat Cable Composed of CuNb-Reinforced Nb3Sn Strands
Adv. Cryo. Eng. 60 (2014) 186-191
K. Watanabe, H. Oguro, S. Awaji, H. Kumakura1, M. Sugimoto2 and H. Tsubouchi2
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 National Institute for Materials Science, Tsukuba 305-0047, Japan
2 Furukawa Electric Co., Nikko 321-1493, Japan
abstract
A Rutherford flat cable that is applicable for operational currents up to 1000 A at 13-14 T was developed using a bronze-processed high-strength Nb3Sn strand with CuNb reinforcement (CuNb/Nb3Sn). The critical current for a 0.8-mm diameter CuNb/Nb3Sn strand is 98 A at 14 T and 4.2 K in the residual strain state. A test coil using the CuNb/Nb3Sn Rutherford flat cable composed of 16 CuNb-reinforced Nb3Sn strands was fabricated. We measured the critical current properties of the Rutherford test coil and obtained an excellent critical current of 1840 A at 14 T and 4.2 K. By using the strain gauges attached onto the stainless-steel reinforcement tape that was co-wounded with the Rutherford flat cable, it was found that a 300-MPa hoop stress at 4.2 K was applied to the CuNb/Nb3Sn strand. This implies that the critical current for a CuNb/Nb3Sn strand is enhanced to be 115 A at 14 T and 4.2 K through the stress-strain effect of the critical current at 300 MPa.
2：Construction of a 25-T Cryogen-Free Superconducting Magnet
Journal of Physics: Conference Series. 568 (2014) 032019
K. Watanabe, S. Awaji, H. Oguro, Y. Tsuchiya, S. Hanai1, H. Miyazaki1, T. Tosaka1, M. Takahashi1 and S. Ioka1
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Toshiba Corporation, Yokohama, 230-0045, Japan
abstract
The construction of a 25-T cryogen-free superconducting magnet (25T-CSM) has started in 2013 at the High Field Laboratory for Superconducting materials, Institute for Materials Research, Tohoku University. The 25T-CSM consists of a low-Tc (LTS) coil and a high-Tc superconducting (HTS) coil. A high-strength CuNb/Nb3Sn Rutherford cable with the reinforcing stabilizer CuNb composite is adopted for the middle LTS section coil. The characteristic feature of the new technology using a CuNb/Nb3Sn Rutherford cable is a react-and-wind method for the coil-winding process. The LTS coil of 300-mm winding inner diameter is fabricated, and a central magnetic field of 14 T is generated at an operation current of 851 A. The HTS insert coil wound with GdBa2Cu3Oy (Gd123) tape has a 52-mm experimental room temperature bore, and a central magnetic field of 25.5 T will be generated at an operation current of 150 A in a background field of 14 T.
3：High Static Magnetic Field Facilities for New Materials Development in Japan
Proceedings of the Twenty-second International Conference on Composites/Nano Engineering (ICCE-22)
K. Watanabe, S. Awaji, H. Oguro, Hiroyuki Nojiri, Takahiko Sasaki, Tadashi Shimizu1, and Hiroaki Kumakura1
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 National Institute of Materials Science, Tsukuba 305-0047, Japan
abstract
A magnetic field is an important thermodynamic parameter in solid state physics and materials science. The large magnetic field environment required for fundamental research has certainly led to novel, direct observation of the quantum effect. New quantum ground states such as the quantum Hall effect in fields with strength 25-35 T and the magnetic-field-induced superconducting state in fields with strength 35-45 T have been discovered. In addition, different extreme conditions of low temperature and high pressure at a high, constant magnetic field can provide a great opportunity to further deepen basic research.
In addition, for materials science it is necessary to evaluate the magnetic-field effect for synthesizing new functional materials under high magnetic field conditions. In particular, materials science needs a long-term experiment with a large constant field using a superconducting magnet. The improvement of high-field superconductors will allow the realization of an advanced superconducting magnet system. This will allow high-field superconducting technology to make significant progress in the development of high-resolution NMR superconducting magnets and practical high-field superconducting magnets for use in fusion reactors and ion-beam accelerators.
Therefore, the next-generation high-field facility is required to generate large static magnetic fields up to 50 T for precise experimentation. As the present status of static high magnetic field facilities in the world, the large-scale facilities such as the 32MW-45T National High Magnetic Field Laboratory (NHMFL) in the United States and the 23MW-36T Grenoble High Magnetic Field Laboratory (GHMFL) in EU have made great progress in construction. Recently, the Science Council of Japan has adopted that Japan should build a new high magnetic field facility with a 24MW power supply system to develop a 50 T hybrid magnet, which will be operated by the all-Japan organization consisting of the National Institute of Materials Science and Tohoku University.
2013年
1：Heat-treatment processing for MnBi in high magnetic fields
Adv. Sci. Tech. 78 (2013) 19-24
K. Watanabe, Y. Mitsui and K. Koyama1
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan
abstract
The phase diagram for MnBi was investigated in high fields up to 18 T at temperatures ranging from 300 to 730 K. We used the differential thermal analysis (DTA), in order to examine the equilibrium phase change of ferromagnetic MnBi by applying high magnetic fields. In particular, the first-order magnetic phase transition to the paramagnetic phase at the decomposition temperature Tt ~ 628 K for ferromagnetic MnBi was evaluated in fields up to 26 T. It was found that Tt increases with increasing magnetic fields at the rate of 2 K/T in low fields up to 18 T, and clearly deviates from the linear increase above 20 T. From a viewpoint of application, it is important that the decomposition of MnBi can be controlled by a magnetic field. As a result, Tt on the liquid phase line changes the amount of Mn content from 10 to 16.5at.% at 26 T, and the heat-treatment at 26 T improves the volume fraction of MnBi. Further, it is quite interesting to directly synthesize ferromagnetic MnBi from the liquid phase without the paramagnetic phase transformation.
2：Wide Variety of Experiments Using a Cryogen-Free 27.5 T Hybrid Magnet and a Cryogen-Free 18.1 T Superconducting Magnet
J. Low Temp. Phys. 170 (2013) 503-510
K. Watanabe, S. Awaji and H. Oguro
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
abstract
A cryogen-free hybrid magnet without liquid helium for operation, generating 27.5 T in a 32 mm room temperature bore of an 8 MW water-cooled resistive insert magnet in an 8.5 T background field of a cryogen-free superconducting outsert magnet, is being operated for basic research at low temperatures down to 17 mK in combination with a dilution refrigerator. In addition, we are developing functional materials using a differential thermal analysis DTA at high temperatures up to 1400 K in high fields up to 27 T. This cryogen-free hybrid magnet will be upgraded to generate 29 T by improving the outer superconducting magnet.
A cryogen-free 18.1 T superconducting magnet with a 52 mm room temperature experimental bore, consisting of a Bi2Sr2Ca2Cu3O10 (Bi2223) insert coil, has been developed using a GM-JT cryocooler. Recently, bronze-tape-laminated Bi2223 has revealed excellent irreversible stress tolerance of 250 MPa at 77 K. In addition, the critical current properties for recent Bi2223 tapes are largely improved from 200 to 400 A/cm-width at 77 K in a self-field. Therefore, the stainless steel reinforcement tape incorporated for the previous Bi2223 insert coil is no longer needed for a new Bi2223 one. A new Bi2223 insert coil with almost the same size as the existing insert coil can generate two times higher fields at the elevated operation current from 162 to 191 A. An upgraded cryogen-free superconducting magnet can offer a long-term experiment at the constant magnetic field of 20 T for an in-field heat-treatment investigation.
3：Upgrade Design to a Cryogen-Free 20-T Superconducting Outsert for a 47-T Hybrid Magnet
IEEE Trans. Appl. Supercond. 23 (2013) 4300304 (4pp)
K. Watanabe, S. Awaji, Y. Hou, H. Oguro, T. Kiyoshi1, H. Kumakura1, S. Hanai2, H. Tsubouch3, M. Sugimoto3 and I. Inoue3
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 National Institute for Materials Science, Tsukuba 305-0047, Japan
2 Toshiba Corporation, Yokohama 230-0045, Japan
3 Furukawa Electric Co., Nikko 321-1493, Japan
abstract
A Rutherford flat cable composed of sixteen 0.8-mm-diameter Nb3Sn strands with CuNb-reinforced stabilizers (CuNb/Nb3Sn) has been developed for use as an outsert for a 47-T hybrid magnet. To guarantee the safety of the magnet in the event of a quench, the low residual resistance ratio (RRR) characteristic of arc-melted-in-situ CuNb composite had to be improved upon, and to obtain high electric conductivity, a new CuNb fabrication method using a Nb rod was attempted.
The thermal runaway characteristics of chemical vapor deposition (CVD)-YBa2Cu3O7-δ (Y123) coated-conductor tapes with varying Cu stabilizer thicknesses were measured in magnetic fields of up to 10 T at temperatures ranging from 17 to 60 K. It was found that the ratio of the thermal runaway over-current to the critical current decreases as temperature decreases and that thermal runaway occurs just above the critical current level at 5 K.
The properties of a cryogen-free, 20-T superconducting outsert for a 47-T hybrid magnet utilizing CuNb/Nb3Sn Rutherford flat cables and Y123 tapes and having a room temperature bore of 400 mm were investigated.
2012年
1：Hybrid Magnet Design Consisting of a 20 T Superconducting Outsert and a 15 MW Resistive Insert
IEEE Trans. Appl. Supercond. 22 (2012) 4300804 (4pp)
K. Watanabe, S. Awaji, H. Oguro, K. Takahashi, K. Minegishi, T. Suwa, Y. Sasaki, T. Kiyoshi1, T. Asano1, S. Hanai2, H. Tsubouchi3 and I. Inoue3
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 National Institute for Materials Science, Tsukuba 305-0047, Japan
2 Toshiba Corporation, Yokohama 230-0045, Japan
3 Furukawa Electric Co., Nikko 321-1493, Japan
abstract
Internally reinforced Nb3Sn strands with CuNb-reinforcing stabilizer (CuNb/Nb3Sn) have been developed for realizing a compact high-field superconducting magnet. The Rutherford flat cables composed of sixteen strands were made with a 0.8 mm diameter CuNb/Nb3Sn strand. The designed critical current of the CuNb/Nb3Sn Rutherford flat cable is Ic = 1890 A at 13 T and 4.2 K in case of an ordinary heat-treatment at 670 ºC for 96 h, which is two times higher than an operation current desired for safety margin.
In addition, mechanical characteristics for CVD-processed YBa2Cu3O7 (YBCO) coated-conductor tapes were measured at 4.2 K in fields up to 18 T. It was found that YBCO tape exhibits the irreversible strain 0.5% and the irreversible stress 1140 MPa for the critical current at 4.2 K and 18 T for B//c.
The cabling-and-react+prebending-processed CuNb/Nb3Sn Rutherford flat cables and CVD-processed YBCO tapes will be used as a react-and-wind method for the development of a 20 T superconducting magnet with a wide room temperature bore. We design a 20 T–440 mm warm-bore superconducting magnet consisting of YBCO inner coils, Nb3Sn middle coils, and NbTi outercoils, which has the coil parameters of inner diameter 480 mm, outer diameter 1283 mm, and coil height 1302 mm. Since the coil inductance is estimated to be 232 H, the magnetic stored energy is 94 MJ at an operation current 900 A. An energy-saving 47 T hybrid magnet can be constructed in combination with a wide-bore 20 T superconducting outsert and a 15 MW–27 T water-cooled resistive insert.
2：Compact 20 T Superconducting Magnet for a 50 T-Class Hybrid Magnet
Adv. Cryo. Eng. 58 (2012) 252-257
K. Watanabe, S. Awaji, H. Oguro, S. Hanai1 and H. Tsubouchi2
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Toshiba Corporation, Yokohama 230-0045, Japan
2 Furukawa Electric Co., Nikko 321-1493, Japan
abstract
The repeated prebending treatment for Nb3Sn wires with CuNb reinforcing stabilizer (CuNb/Nb3Sn) largely enhances the critical current. Since the employment of the highstrength CuNb/Nb3Sn wire is very effective for a react-and-wind process Nb3Sn superconducting magnet, we focus on the application of this prebending effect to the react-and-wind process of high-strength strand cables. The Rutherford flat cables composed of sixteen CuNb/Nb3Sn strands were fabricated to be applicable to the react-and-wind method. High-strength CuNb/Nb3Sn strand cables will exhibit the critical current of Ic = 1890 A at 13 T and 4.2 K. In order to construct a compact hybrid magnet, a 20 T-440 mm room temperature bore superconducting magnet consisting of YBCO, CuNb/Nb3Sn, and NbTi section coils is designed, using such Rutherford flat cables in pool-boiling liquid helium.
2011年
1：Cryogen-free 23 T superconducting magnet employing an YBa2Cu3O7 coated conductor insert
J. Supercond. Nov. Magn. 24 (2011) 993-997
K. Watanabe, S. Awaji, G. Nishijima and S. Hanai1
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Toshiba Corporation, Yokohama 230-0045, Japan
abstract
We have successfully constructed an 18.1 T superconducting magnet conductively cooled by a GM/JT cryocooler. The double-pancake insert using Ag-sheathed Bi2Sr2Ca2Cu3O10(Bi2223) tape with stainless steel reinforcement tape generated 2.5 T in a 15.6 T background magnet. In order to develop a cryogenfree high field superconducting magnet producing over 20 T, an YBa2Cu3O7(Y123) coated conductor insert is intended for upgrading the cryogenfree 18 T superconducting magnet. The Bi2223 insesrt, whose size is 176 mm outer diameter, 90 mm inner diameter, and 252 mm coil height, is now excited at 162 A operation current, and will be replaced by a new Y123 insert. We have already confirmed excellent mechanical properties of 1000 MPa hoop stress tolerance for Y123 coated conductor tape with Hastelloy substrate. This means that we no longer need stainless steel reinforcement for the insert. As a result, an Y123 insert with almost the same size as the Bi2223 insert is designed to generate 7.5 T at 187 A, because the number of turns can be improved extremely. A cryogenfree 23 T superconducting magnet can sufficiently be developed for a long-term experiment at a constant high magnetic field.
2：Thermal Stability Properties of YBa2Cu3O7 Coated Conductor Tape under the Cryocooling Condition
IEEE Trans. Appl. Supercond. 21 (2011) 2449-2452
K. Watanabe, V. R. Romanovskii1, R. Ishihara, G. Nishijima, S. Awaji,
I. Inoue2, H. Sakamoto2, M. Mimura2 and S. Nagaya3
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 the Russian Research Center "Kurchatov Institue," Moscow 12382, Russia
2 the Furukawa Electric Co., Ltd., Nikko 321-1493, Japan
3 the Chubu Electric Power Co., Inc., Nagoya 459-8522, Japan
abstract
From the viewpoint of a cryogen-free high-field superconducting magnet, the thermal stability properties of YBa2Cu3O7 (Y123) coated conductor tapes before thermal runaway are examined under the conduction-cooling condition by a GM-cryocooler. Under such cryocooling condition, Ag-sheathed Bi2Sr2CaCu2O8 (Bi2212) wires with Jc〜104 A/cm2 reveal stable behaviors of 3 times larger current properties before thermal runaway than critical currents, although conventional Nb3Sn wires with Jc〜104 A/cm2 quench almost at their critical currents under the cryocooling condition. In order to determine the maximum current-carrying capacity of the Y123 tape in high fields, we use a zero-dimensional heat balance model. On the basis of the measured basic properties for the Y123 tape, the calculations were done at B=20 T, bath temperature T0=4.2 K, Jc〜107 A/cm2, and cryocooling heat transfer coefficient h=10-3 W/cm2 K. We found that the Y123 tape with Jc〜107 A/cm2 does not have the over-critical current but rather the sub-critical current before thermal runaway.
2010年
1：Tohoku High Magnetic Field Research Activities Using Cryogen-Free Superconducting Magnets
J. Low Temp. Phys. 159 (2010) 370-373
K. Watanabe, S. Awaji, K. Koyama, G. Nishijima, K. Takahashi and Y. Sasaki
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
abstract
In order to realize a hybrid magnet with no need of liquid helium for operation, we have designed a 28 T cryogen-free hybrid magnet with a 32 mm room temperature experimental bore, and actually tested to generate the peak field of 27.5 T. An easy-to-operate cryogen-free hybrid magnet is now operating for basic research in high fields up to 27 T at low temperatures down to 40 mK, using a dilution refrigerator. In addition, we are intending to develop a 100 mm wide bore water-cooled resistive insert magnet combined with a cryogen-free superconducting outsert magnet for X-ray diffraction measurements in steady magnetic fields up to 20 T.
It found that YBa2Cu3O7 (Y123) coated conductor tape with Hastelloy substrate has the excellent mechanical property of 1000 MPa hoop stress tolerance. We are carrying out the research and development of a 30 T all superconducting magnet immersed in liquid helium and a 23 T cryogen-free superconducting magnet, employing Y123 tape.
2：Strain Gauge Method for Evaluating a Three-Dimensional Residual Strain State in Nb3Sn Wires
IEEE Trans. Appl. Supercond. 20 (2010) 1420-1423
K. Watanabe, H. Oguro1, K. Minegishi, S. Awaji and G. Nishijima
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Ibaraki University, Tokai 319-1106, Japan
abstract
Concerning the strain effect of superconducting properties for Nb3Sn wires, it is necessary to investigate a three-dimensional strain state that Nb3Sn superconductors truly experience in the composite wire. However, it is very difficult for Nb3Sn wires to obtain the three-dimensional residual strain components experimentally. We adopted the strain gauge that is directly glued onto the 1mm outer diameter Nb3Sn wire, in order to quantitatively measure the three-dimensional distortions. To evaluate axial and lateral distortions of the wire, strain gauges were set in both axial and lateral directions. This measurement system can obtain the distortion detail in fields up to 27 T at temperatures ranging from 4.2 to 20 K. We measured the upper critical field Bc2 in a three-dimensional strain state for Nb3Sn wires. It was found that the wire architecture changes each residual strain in axial and lateral directions of the wire. Moreover, the Bc2 strain sensitivity that is related to the Bc2 variation is also affected by its architecture. We found that the axial tensile strain variation 0.3 % roughly corresponded to the lateral compressive strain variation 0.1% for Nb3Sn wires. This means that the ratio of the lateral strain and the axial one for Nb3Sn wires is 0.3. The ratio of both residual strains in the axial and lateral directions is very important to examine the strain effect of Nb3Sn wires in detail.
3：Grain Morphology for Bi2Sr2CaCu2O8 Tapes Heat-Treated in High Magnetic Fields
Adv. Sci. Technol. 75 (2010) 187
K. Watanabe, T. Inoue and S. Awaji
High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University
abstract
We prepared Ag-sheathed Bi2Sr2CaCu2O8 (Bi2212) tapes heat-treated in high fields (in-file heat-treatment Bi2212) and heat-treated without magnetic fields (out-of-field heat-treatment Bi2212), in order to examine the magnetic field effect on the microstructure of Bi2212. The differential thermal analysis (DTA) was performed at 10 T using Bi2212 powders. The DTA suggests that the in-field heat-treatment changes the grain morphology of Bi2212. It was found that the critical current density Jc for the in-field heat-treatment Bi2212 tapes is largely improved at 10 K in fields. In addition, the in-field heat-treatment Bi2212 tape has also a large n-value in the form of E=Ec(J/Jc)n, which is related to the microstructure change.
2009年
1：Cryogen-Free 23 T Superconducting Magnet with a 7.5 T YBa2Cu3O7 Insert Coil
Appl. Phy. Express 2 (2009) 113001
Kazuo Watanabe, Satoshi Awaji, Gen Nishijima
Satoshi Hanai1, and Michitaka Ono1
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Toshiba Corporatiion, Yokohama 230-0045, Japan
abstract
In order to develop a cryogen-free high-field superconducting magnet generating over 20 T, a Y123-coated conductor insert coil is used to enhance a cryogen-free 18 T superconducting magnet. The Y123 tape does not require stainless steel reinforcement. The Y123 insert coil, which is almost the same size as the current Bi2223 inseert coil, is designed to generate 7.5 T at 187 A. It is able to achieve this since without stainless steel reinforcement the number of turns can be greatly increased. A cryogen-free superconducting magnet can achieve a static magnetic filed of 23 T, which is higher than that generated by practical superconducting magnets using liquid helium.
2：20 T Compact Superconducting Outsert Employing Y123 Coated Conductors for a 45 T Hybrid Magnet
IEEE Trans. Appl. Supercond. 19 (2009) 1592-1595.
K. Watanabe, S. Awaji, G. Nishijima
T. Hamajima1
T. Kiyoshi2, H.Kumakura2, S. Hanai2
S. Hanai3, K. Koyanagi3, and M. Ono3
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Graduate School of Engineering, Tohoku University, Sendai 980-8577, Japan
2 Natioinal Institute for Material Science, Tsukuba 305-0047, Japan
3 Toshiba Corporation, Yokohama 230-0045, Japan
abstract
We have been developing high-strength Nb3Sn strand cables to construct a high-field superconducting onutsert for a 45 T hybrid magnet with a 25 T water-cooled resistive magnet. Evidence for cold work strengthening of repeated bending treatment (prebending effect) on Nb3 strands internally reinforced with CuNb stabilizer, which exhibits significant enhancement of the critical current density, has been found in the superconducting magnet fabrication process using a react-and-wind method. The strand cables were designed by controlling the constituent number of CuNb/Nb3Sn strands with the prebending effect and stainless steel strands, which are expected to have a stress limit 580 MPa at 0.4 % strain. In order to design a compact superconducting outsert, high-strength strand cables are adopted in a magnetic field region below 14 T to maintain relatively large engineering current densities (je). In a higher-field region above 14 T, YBa2Cu3O7 (Y123) coated conductors are employed for an insert coil. Using combination of Y123, Nb3Sn and NbTi superconductors, a 20 T superconducting outsert with a room temperature bore of 400 mm consisting of three layers made of Y123, two layers of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are 440 mm inner diameter, 1080 mm outer diameter and 1138 mm coil height. A very compact 20 T superconducting outsert with a stored magnetic energy 72 MJ at an operatiion current 903 A can be developed for a 45 T hybrid magnet.
3：冷媒を使わずにどこまで温度を下げられるか
パリティ 24 No.7 (2009) 40-44.
渡辺和雄
東北大学金属材料研究所
温度を下げる方法は，低温物理学そのものである。温度はどこまで下がったであろうか。現在では，金属試料をμK(10-6K)の温度領域まで冷却する超低温領域まで達している。この低温技術は，液体ヘリウムを使用して実現できたものであるが，最近は小型冷凍機の発展により液体ヘリウムの冷媒を必要としない状況になりつつある。小型冷凍機は，ヘリウムガスの閉ループ方式なので，利用者にとっては直接に冷媒を一切使わない無冷媒の冷却方式である。冷蔵庫を使用する場合と同じで，利用者は冷媒が閉ループのため全く気にする必要がない。最近，液体ヘリウムを用いた超電導マグネットは小型冷凍機冷却方式の超電導マグネットに置き換えられるようになり，小型冷凍機冷却超電導マグネットは無冷媒超伝導マグネットと呼ばれている。この意味において，小型冷凍機が適用された閉ループ冷却システムは，利用者にとって冷媒を使わない冷却方式と定義することができる。以下では，液体ヘリウムを冷媒とした低温技術がどのようにして温度を下げて行ったかを振り返り，小型冷凍機冷却方式を採用することで直接的な冷媒を使わずにどこまで温度を下げられるかを見てみたい。
4：日本における低温技術
低温ジャーナル 3 (2009) 10-14.
渡辺和雄
東北大学金属材料研究所
東北大学金属材料研究所の１号館正面玄関の奥に、我が国で初めてのヘリウム液化機が展示されている。米国Little製のCollins型ヘリウム液化機である。日本における注目すべき低温技術は、ヘリウム液化機の大型化、極低温から超低温までの極・超低温の生成技術、そして磁性蓄冷材と小型冷凍機の開発の３テーマである。低温技術として、超電導マグネット技術の詳細に関しては割愛したい。以下に、日本における低温技術の発展状況と特色をまとめてみる。
2008年
1：Compact Design of a 30 T Superconducting Magnet Incorporating YBa2Cu3O7
Coated Conductor Tapes and Pre-reacted Nb3Sn Strand Cables
Appl. Phys. Express 1 (2008) 101703.
Kazuo Watanabe, Gen Nishijima, Satoshi Awaji,
Takataro Hamajima1, Tsukasa Kiyoshi2, Hiroaki Kumakura2,
Kei Koyanagi3, Satoshi Hanai3, and Michitaka Ono3
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
1 Graduate School of Engineering, Tohoku University, Sendai 980-8578, Japan
2 National Institute for Materials Science, Tsukuba 305-0047, Japan
3 Toshiba Corporation, Yokohama 230-0045, Japan
abstract
We set out to design as compactly as possible a 30 T superconducting magnet consisting of an YBa2Cu3O7 (Y123) insert coil and a CuNb-reinforced Nb3Sn (CuNb/Nb3Sn) background coil. The engineering current density Je for an Y123-coated conductor tape is larger at 14–15 T and 4.2 K than that for a CuNb/Nb3Sn strand. Adopting Y123-coated conductor tapes in the high field region above 14–15 T proves highly effective for the fabrication of a very compact 30 T superconducting magnet. A 30 T, 52 mm-room-temperature bore superconducting magnet can be constructed in the coil grading of a 16 T Y123 insert and a 14 T CuNb/Nb3Sn background coil, and the stored magnetic energy of 32 MJ successfully lies in the 1/3 level in comparison with the 30 T nuclear-magnetic-resonance (NMR) superconducting magnet reported previously.
2： Current-Carrying Capacity of YBa2Cu3O7-Coated Conductors
for a 30 T Superconducting Magnet
Appl. Phys. Express 1 (2008) 081701.
Kazuo Watanabe, Vladimir R. Romanovskii1, Satoshi Awaji,
Gen Nishijima, Hiroyuki Matsuo
1 Russian Research Center, Kurchatov Institute, Moscow 123182, Russia
abstract
A 30 T superconducting magnet employing Ag/YBa2Cu3O7/Hastelloy (Y123) coated conductors would make precise fundamental research much more accessible. In order to investigate the feasibility of such a magnet, the current stability of the conductor was examined at 30 T for B//c. Liquid helium cooled Y123-coated conductors with copper and silver stabilizing layers were examined for coil quench issues. Instability conditions were studied using a static zero-dimensional model for various copper stabilizing-layer thicknesses. The calculations indicate the existence of a stable sharing current in the copper stabilizer, of about 0.7 A per 1 μm of copper thickness at 30 T in liquid helium. This sharing current in the copper stabilizer can be added to the 140 % critical current of the Y123 conductor at 30 T for B//c.
3：Case Study of a 20 T-φ400 mm Room Temperature Bore Superconducting Outsert
for a 45 T Hybrid Magnet
IEEE Trans. Appl. Supercond. 18 (2008) 552-555
K. Watanabe, S. Awaji, G. Nishijima,
T. Hamajima, T. Kiyoshi, H. Kumakura, S. Hanai, and M. Ono
abstract
The High Field Laboratory for Superconducting Materials (HFLSM) and the Tsukuba Magnet Laboratory (TML) conducted in collaboration a case study on development of a 50 T-class hybrid magnet. To construct a high magnetic field magnet with compact and energy-saving design as well as with easy operation and maintenance, one has to develop high-strength Nb3Sn strand cables, with maximized superconducting characteristics and which can withstand a large electromagnetic force over 500 MPa. For this purpose, the HFLSM has proposed and investigated the effect of repeated bending treatment (prebending) on
Nb3Sn strands internally reinforced with CuNb stabilizer leading to significant enhancement of the critical current density. In this report we present our results on application of the prebending effect to the development of high-strength strand cables. The designed prebent-strand cables are composed of three CuNb/Nb3Sn strands (3 xφ1.73 mm) and four stainless steel strands (4 xφ1.73 mm). High-strength CuNb/Nb3Sn strand cables have shown a stress limit of 552 MPa at 0.4 % strain, and a critical current of Ic = 1000 A at 18.5 T and 2.0 K.
For such high-strength strand cables, a 20 T superconducting magnet with a room temperature bore (φ400 mm) consisting of five layers made of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are: inner diameterφ440 mm, outer diameterφ1332mm, coil height 1321 mm, inductance 350 H and magnetic stored energy 144 MJ at 908 A of the operation current. Winding of the coil was experimentally successfully simulated using dummy 3+4 strands cable composed of three Cu strands and 4 stainless steel strands with a similar design to the 3+4 strands superconducting cable presented above. The 20T superconducting coil will be used as a 20 T outsert for a 25 T water-cooled resistive insert to obtain a 45 T hybrid magnet.
4：High-Strength CuNb/Nb3Sn Strand Cables with Residual Strain Controlled
by the Repeated Bending Treatment
J. Phys. Conf. Ser. 97 (2008) 012008
K Watanabe1, H Oguro1, P Badica1, S Awaji1, G Nishijima1,
H Tsubouchi2 and S Meguro2
1 High Field Laboratory for Superconducting Materials,
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2 Furukawa Electric Co., Ltd., Nikko 321-1493, Japan
abstract
We have developed practical multifilamentary Nb3Sn wires with CuNb composite reinforcement (CuNb/Nb3Sn). In order to fabricate a CuNb/Nb3Sn superconducting magnet by a react-and-wind method, the bending strain effect was investigated in detail for CuNb/Nb3Sn wires. We found that the repeated bending treatment enhances Tc from 17.4 to 17.9 K and Bc2 from 24.0 to 25.3 T at 4.2 K for CuNb/Nb3Sn wire. As a result, the repeated bending treatment for CuNb/Nb3Sn wire outstandingly enhances the critical current in high magnetic fields. A Nb3Sn filament was prepared by chemically solving practical multifilamentary CuNb/Nb3Sn wires. After removing Cu stabilizer, CuNb reinforcement, Nb barrier, and Bronze, Bc2 of a Nb3Sn filament was measured, and the Bc2 value of 25.9 T at 4.2 K was obtained. This means that the bending treatment for CuNb/Nb3Sn wires extremely reduces the residual strain close to the strain free state. To decrease the residual strain, it is important to control the three-dimensional strain distribution of CuNb/Nb3Sn wires.
We intended to apply the bending effect to the cabling process of CuNb/Nb3Sn strands by a react-and-wind method. High strength Nb3Sn cables consisting of CuNb/Nb3Sn strands and stainless steel reinforcement strands were developed for a performance test of a next phase superconductor with a large critical current and a strong mechanical property at a high magnetic field of 20 T.
5：Ag-Sheathed Bi2Sr2CaCu2O8 Square Wire Insulated
with Oxidized Hastelloy Fiber Braid
Adv. Cryo. Eng. 54 (2008) 439-444
K. Watanabe1, G. Nishijima1, S. Awaji1,
Y. Hikichi2, and T. Hasegawa2
1 High Field Laboratory for Superconducting Materials,
Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
2 SWCC Showa Cable Systems Co., Ltd., Kanagawa, 229-1133, Japan
abstract
Oxidized Hastelloy X (Hx) fiber braid has been demonstrated to work well as a good electric insulation of Ag-sheathed Bi2Sr2CaCu2O8 (Ag/Bi2212) wires. In order to develop a wind-and-react processed Ag/Bi2212 superconducting magnet with a high coil current density, we fabricated a test coil employing 45 m long Ag/Bi2212 square shape wire with 50 m Hx fiber braid. A test coil, whose size is 73 mm outer diameter, 64.5 mm inner diameter, and 74 mm coil winding height, consisted of 4 layers and 210 turns, and was heat-treated at around 890˚C in oxygen gas. The critical current Ic of the test coil was 245 A at 4.2 K in a self-field, corresponding to a 67% value of the short sample Ic heat-treated at the same time for comparison. Coil inductance was calculated to be 1.9 mH, and as a result, the same inductance value was obtained in the test coil. It was found that a Hx cloth knitting method enables us to insulate sufficiently between wires in Ag/Bi2212 square shape wire.
6：Vortex pinning phase diagram for various kinds of
c-axis correlated disorders in RE123 films
Journal of Physics: Conference Series 97, 1 (2008) 012328
Awaji, S.a, Namba, M.a, Watanabe, K.a, Nojima, T.a ,
Okayasu, S.b, Horide, T.c, Mele, P.d, Matsumoto, K.d,
Miura, M.e, Ichino, Y.e,Yoshida, Y.e, Takai, Y.e,
Kampert, E.f, Zeitler, U.f, Perenboom, J.f
a Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
b JAEA, Ibaraki 319-1195, Japan
c Kyoto University, Kyoto 606-8501, Japan
d Kyushu Inst. Techn., Kita-kyushu 804-8550, Japan
e Nagoya University, Nagoya 464-8603, Japan
f High Field Magnet Lab., IMM, Radboud University Nijmegen, NL-6525 ED Nijmegen, Netherlands
abstract
The critical current density Jc and resistivity ρ of REBa2Cu3Ox (RE123) films were evaluated in high magnetic field and wide temperature regions. We use three different samples such as a heavy ion irradiated Y123 film, a BaZrO3 (BZO) added Y123 film and a low temperature growth Sm1-xBa2+xCu 3Oy (LTG-Sm123) film. In these films, there exist the different c-axis correlated disorders like columnar shaped fission tracks for the heavy ion irradiated Y123 film, columnar shaped BZO precipitates for the BZO added Y123 film and edge dislocations at grain boundaries for the LTG-Sm123 films. The large peak of the angular dependence of Jc for B//c direction was observed for all samples measured in this study in a low field region, suggesting that the c-axis correlated pinning works well for these samples. However, we found that the behavior of the Jc peak for B//c strongly depends on a sort of c-axis correlated pinning centers. In the case of the columnar shaped fission tracks in the Y123 film, the Jc peak for B//c increases monotonically with increasing a magnetic field and seems to be connected with the dip structure in the angular dependence of ρ. In the case of the columnar shaped BZO precipitates, however, the Jc peak for B//c vanishes in a high field region above a few tesla and no dip behavior of ρ was observed. On the contrary, in the case of the edge dislocations for LTG-Sm123 film, the Jc peak for B//c shrinks with increasing field and almost vanishes. But it grows again with further increasing a magnetic field and the dip of the angular dependence of ρ is also observed. Hence the vortex pinning phase diagram strongly depends on a sort of c-axis correlated pinning centers. It is considered that these different behaviors of the J c peak for B//c are related to the competition of the random and c-axis correlated pinnings.
7：Magnetization measurements of DyB2C2
under high pressure and high magnetic fields
Physica B: Condensed Matter 403,5-9 (2008) 1607-1608
Koyama, K.a, Onodera, H.b, Watanabe, K.a
a High Field Laboratory for Superconducting Materials, Institute for Materials Research,
Tohoku University, Sendai, 980-8577, Japan
b Department of Physics, Graduate School of Science,
Tohoku University, Sendai, 980-8578, Japan
Abstract
Magnetization measurements were performed on a DyB2 C2 single crystal under pressures up to 1.0 GPa in high magnetic fields up to 26 T. At 4.2 K, pressure-induced magnetic phases are found below 8 T along the [1 0 0] axis, which varies for pressures and temperatures.
8：Magnetic and structural phase transitions of MnBi
under high magnetic fields
Science and Technology of Advanced Materials 9,2 (2008) 024204
Koyama, K., Mitsui, Y., Watanabe, K.
High Field Laboratory for Superconducting Materials, Institute for Materials Research,
Tohoku University, Sendai, 980-8577, Japan
Abstract 1: High-Strength Nb3Sn Wire Development K. Watanabe, S. Awaji and G. Nishijima abstract 2: Magnet Science and Technology for Basic Research WATANABE Kazuo abstract 3: CHALLENGING DEVELOPMENT OF A CRYOCOOLED 8 MW–34 T HYBRID MAGNET K. Watanabe1, K. Takahashi1, G. Nishijima1, S. Awaji1, abstract 4: 銀シースBi2212超伝導体の極微小抵抗状態における熱的安定性 渡辺 和雄1,V.R. ROMANOVSKII 1,2，西島 元1，淡路 智1 abstract
High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature TSR(=90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of TSR. By applying a magnetic field of 5 T, the parameter a increases by ∼0.05% when T2007年
for Compact Superconducting Magnets
Materials Science Forum 546-549 (2007) 1841-1848.
High Field Laboratory for Superconducting Materials, Institute for Materials Research,
Tohoku University, Sendai 980-8577, Japan
A cryogen-free 18.1 T superconducting magnet with a 52 mm room temperature experimental bore, consisting of a Bi2Sr2Ca2Cu3O10 (Bi2223) insert coil, Nb3Sn intermediate coils, and a NbTi outer coil, has been developed using a GM-JT cryocooler with a cooling capacity of 4.3 W at 4.3 K. Three power supplies were individually adopted to energize three kinds of coils. The double-pancake insert coil using Ag-sheathed Bi2223 tape with stainless steel reinforcement tape generated 2.5 T in a 15.5 T background Nb3Sn/NbTi magnet. The Bi2223 insert coil with a size of 176 mm outer diameter, 90 mm inner diameter, and 252 mm coil height can be easily replaced by a new YBa2Cu3O7 (Y123) insert coil. Y123 coated conductor tape with Hastelloy substrate revealed excellent mechanical properties of 1000 MPa hoop stress tolerance. The 4.3 mm wide and 0.4 mm thick stainless steel reinforcement for the Bi2223 insert coil is no longer needed for a new Y123 one. A designed Y123 insert coil with almost the same size as the Bi2223 insert coil will generate 7.5 T at 187 A. As a result, a cryogen-free 23 T superconducting magnet can be developed for a long-term experiment at a constant high magnetic field over 20 T.
at the High Field Laboratory for Superconducting Materials
Adv. Technol. Electrical Engineering and Energy 26 (2007) 59-64
High Field Laboratory for Superconducting Materials,
Institute for Materials Research, Tohoku University
Since the first practical cryocooled superconducting magnet using a GM-cryocooler and high temperature superconducting current leads has been demonstrated successfully at the High Field Laboratory for Superconducting Materials (HFLSM), various kinds of cryocooled superconducting magnets in fields up to 15 T have been used to provide access for new research areas in fields of magneto-science. Recently, the HFLSM has succeeded in demonstrating a cryocooed 18 T high temperature superconducting magnet and a high field cryocooled 27.5 T hybrid magnet. Cryocooled magnet technology and basic research using high field magnets at the HFLSM are introduced.
Proc. Inter. Cryo. Eng. Conf. (ICEC) Prague (2007) 239-242.
T. Itoh2, M. Ishizuka2
1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2 Sumitomo Heavy Industries, Ltd., Yokosuka 237-8555, Japan
We have successfully constructed the unique cryocooled 27.5 T hybrid magnet, consisting of an outer cryocooled 8.5 T superconducting magnet and an inner water-cooled 19 T resistive magnet. In order to upgrade the cryocooled hybrid magnet for obtaining further higher static fields up to 34 T and larger magnetic force fields up to 11000 T2/m, we are now intending to improve the cooling condition of the outer cryocooled 8.5 T superconducting magnet, whose ability is the maximum central field generation up to 11 T. The inner water-cooled poly-Bitter resistive magnet will be designed to generate 23 T at 8 MW in a 16 mm room temperature bore.
Thermal Stability Properties in a Very Low Resistive State of Ag-Sheathed Bi2212 Superconductors
低温工学 42 (2007) 224-229.
Kazuo WATANABE1, Vladimir R. ROMANOVSKII 1,2, Gen NISHIJIMA1 and Satoshi AWAJI1
1東北大学金属材料研究所強磁場超伝導材料研究センター
Institute for Materials Research, Tohoku University, Japan
2Russian Research Center ‘Kurchatov Institute’, Russia 123182, Moscow, Kurchatov Square
Since a low resistive state in high temperature superconductors is quite stable, a current-carrying limitation before thermal runaway is concentrated on as practical application of Ag-sheathed Bi2Sr2CaCu2O8 (Ag/Bi2212) tape. The thermal runaway parameters related with the heat transfer coefficient and Ag matrix resistivity for Ag/Bi2212 tape were investigated. In order to determine the maximum current-carrying capacity of Ag/Bi2212 in a magnetic field, we use the so-called zero-dimensional static model. When the linear temperature model for the critical current density of Ag/Bi2212 is adopted, we can estimate that thermal runaway occurs in one order of magnitude higher electric fields than the critical current criterion of 1x10－6 V/cm for the Ag/Bi2212 tape. This behavior is in good agreement with experimental results. Further, when the nonlinear temperature and magnetic field dependences of the critical current density of Ag/Bi2212 is considered to evaluate the thermal runaway behavior, we found the existence of the multi stable states. The E-J and T-J curves may have the discontinuous parts leading to the jumps of the electric field, current and temperature without the transition of the superconducting composite into the normal state. Moreover, the essential increase of the stable branch of the voltage-current characteristics may be observed.