Site:           Hitachi Laboratory, Hitachi, Ltd.
                1st Department of Energy Research
                Superconductivity Section
                1-1, Omika-cho, 7-chome, Hitachi-shi
                Ibaraki 319-12, Japan
                http://www.hitachi.co.jp/index.html
Date Visited:   June 1996
WTEC Attendees: M. Suenaga (report author), 
                G. Gamota, 
                R. Schwall, 
                R. Sokolowski
Hosts:          Dr. Toshiki Iino, Manager, 
                  First Department of Energy Systems Research
                Kiyoshi Yamaguchi, Senior Researcher
                Ryukichi Takahashi, Senior Researcher, 
                   Superconductivity Center
                Dr. Kazutoshi Higashiyama, Senior Researcher, 
                   Superconductivity Center
                Katsuzo Aihara, Senior Researcher, 
                   Superconductivity Center
                Michiya Okada, Senior Researcher, 
                   Superconductivity Center

BACKGROUND

Hitachi, Ltd., is one of the largest manufacturing companies in Japan. Its business activities cover a broad area, e.g., electronics, consumer products, large computers, heavy equipment for electric power applications, etc. Hitachi, Ltd., also has a long history of working on applications of superconductors. Its investigation of superconductors started in 1965 at the Central Research Laboratory, and in the late 1960s it constructed what was then a very large (5 MJ) magnet with Nb-Zr-Ti wire for the MITI MHD project. Currently, its activities span from a fundamental study of vortex dynamics by Dr. A. Tonomura (his work is well known), to construction of very large magnet systems, such as for the Large Helical Device at the National Institute of Fusion Science (NIFS) at Nagoya and for the International Thermonuclear Experimental Reactor (ITER). In support of these large construction projects at Hitachi Works, the Superconductivity Center of Hitachi Laboratory conducts relatively small-scale research and development on related subjects, and the center also conducts advanced R&D on materials such as conductor development utilizing high T_c superconductors. Table Hitachi.1 summarizes Hitachi's superconductivity research and development.

Table Hitachi.1
Superconductivity Related Research and Development At Hitachi

SUPERCONDUCTIVITY R&D

As listed in Table Hitachi.1, Hitachi Works is actively involved with a number of large-scale projects in Japan. These include magnet systems for magnetically levitated trains (Japan Railways), a rotor for an electrical generator (Super-GM), a large helical magnet for magnetic confinement of plasma for fusion (NIFS), and coils for a superconducting magnetic energy storage (SMES) system (ISTEC). However, much of the small-scale R&D in support of these large-scale construction projects appears to be over, and very little of the related studies seem to be currently conducted at Hitachi Research Laboratory.

In the area of high T_c conductor development, Hitachi Research Laboratory supports approximately 20 full-time scientific staff in superconductivity, and this personnel level may include a number of staff at Hitachi Cables, Ltd., with whom they work very closely on development of both high and low T_c superconducting conductors. Their excellent work on Tl-1223/Ag and Bi-2212/Ag are well known to the community. During this trip, the WTEC panel also learned that they are developing Nb₃Al multifilamentary wires for the ITER program at the Japan Atomic Energy Research Institute. The highlights from these conductor development programs are given below.

Hitachi Research Laboratory has been devoting itself extensively for a number of years to fabrication of practical conductors utilizing Tl-1223 and is essentially the only group in Japan developing Tl-1223 in a conductor form for magnets and other power applications. In spite of some very interesting work, its earlier efforts at wire making with this system were not successful because of the all-too-familiar weak link problems at grain boundaries in the cuprates, but its most recent results on Tl-1223 tapes are very impressive. Its researchers were able to achieve a J_c of 1.5 x 10⁴A/cm² with an electric field criterion of 10^-7V/cm at 77 K and H = 1 T parallel to the plane of a 1.5 µm thick film. The key to this accomplishment was development of a highly biaxially textured Ag tape by the proper thermomechanical treatment of the Ag substrate. In the best case, Hitachi researchers were able to reduce the f scan full width at half maximum (FWHW) to as low as 6 degrees. On this substrate, the precursor without Tl was first deposited, and then the composite was heat-treated to form Tl-1223 in a Tl₂O atmosphere.

Hitachi's work on the development of high current density Bi-2212/Ag multifilamentary tapes is also well known in the community. Okada and his coworkers have shown earlier that the critical current density of the Bi-2212/Ag tapes can be very high at 4.2 K, i.e., nearly 10⁵ A/cm² at magnetic fields as high as H = 23 T. More recently, a Bi-2212 coil (49 mm in OD and 12.5 mm in ID) was made to be tested in a 21 T backup field at the High Magnetic Field Laboratory of the National Research Institute for Metals as a part of its 1 GHz Nuclear Magnetic Resonance Facility project. This coil was successfully tested, and it produced 1.76 T in the 21 T backup field, resulting in a total magnetic field of nearly 22.8 T; this suggests that the required magnetic field for a 1 GHz NMR can be produced using a Bi-2212/Ag insert coil at 4.2 K. Furthermore, in a separate study, Hitachi researchers were able to produce a persistent current mode switch that was incorporated with a Bi-2212 magnet. A rate of magnetic field reduction of 0.4%/h was achieved with the switch in operation. Although the switch requires further reduction in joint resistance and improvement in current carrying capacity, the result that they have attained so far is very encouraging for persistent mode operation of a high T_c magnet at low temperature.

In addition to the above high T_c superconductor conductor development, it was interesting to find out that Hitachi has also developed a very high-quality multifilamentary Nb₃Al wire by a jelly roll process, cooperating with Hitachi Cable, Ltd., for fusion magnets such as for the ITER project. The wire has J_c values in the range of 8 x 10⁴ A/cm² at 12 T, which exceeds the ITER requirement by a comfortable margin. Hitachi researchers have also produced a cable-in-conduit conductor that has carried 20 kA at 12 T. This is impressive. Nb₃Al wire is significantly more difficult to produce than Nb₃Sn wire; however, its mechanical strain tolerance is substantially better than that for Nb₃Sn. Thus, JAERI (Japan Atomic Energy Research Institute) has been encouraging Japanese manufacturers to produce Nb₃Al for the magnets in the ITER project. Earlier, Sumitomo had shown that it is possible to produce practical conductors that can meet the ITER requirement using the jelly roll process. It appears that JAERI is trying to develop other sources for this conductor. All of the above developments are partially supported by government projects, and this appears to be very important to assure internal funding for these projects. The Tl-1223 work is supported as a part of Super-GM; the Bi-2212 is supported as a part of NRIM's 1 GHz NMR project. However, it is interesting to hear that Hitachi is willing to continue the Tl-1223 work, even though the support from Super-GM will terminate when the project is scheduled to close in a couple of years. This may indicate that Hitachi has confidence in the eventual fabrication of a practical conductor with Tl-1223. The WTEC panel's hosts also think that one of the first commercial applications of high T_c superconductors will be power transformers. Yet, interestingly enough, as far the panel is aware, Hitachi had not been reporting in this area nor other possible areas of applications of high T_c superconductors for electrical utility devices at the time of this WTEC visit.