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Japan Atomic Energy Research Institute is constructing the International Thermonuclear Experimental Reactor common test facility for the Central Solenoid Model Coil which is around 180 tons, a forced-flow cooled magnet with the maximum pulsed operation of 2 T/s and generates the rated magnetic field of 13 T at 48 kA with stored energy of 668 MJ. The test facility consists of a coil vacuum chamber, a cryogenic system with the 5-kW refrigerator and 500-g/s cryogenic pump, two pairs of 50-kA current leads, two DC power supplies (50kA and 60kA) and two JT-60 pulsed power supplies (50 kA, [+ or -]4.5 kV and [+ or -]40 kA, [+ or -]1.5 kV). The facility will be demonstrating the refrigeration and operation of a fusion pulsed magnet and the design and construction will accumulate experience towards the construction of ITER.

The ITER-TF coil requires a generation of 12.5 T in a size of 12 m x 18 m. For such a high field-large coil, the applicability of [Nb.sub.3]Al conductors was considered with a react-and-wind technique which realizes high reliability and low cost for the coil fabrication. The maximum bending strain on the [Nb.sub.3]Al conductor in use of this technique is 0.39 %. Ic degradation due to the strain is expected to be below 5 %. The limiting current is estimated as 65 kA for 60 kA operation current. Ac loss in the TF coil with [Nb.sub.3]Al conductor is almost the same as with [Nb.sub.3]Sn conductor.

The Engineering Design Activity (EDA) of International Thermonuclear Experimental Reactor (ITER) has been carried out since 1992 among the four Parties which are European Union, Japan, Russian Federation, and United States. The design and the fabrication of the Center Solenoid (CS) model coil is under way in the ITER-EDA. The CS model coil consists of four parts, which are the outer module, the inner module, insert, and the supporting structure. The design of the CS insert coil is reported and discussed. The inner diameter of the CS insert coil is 1.5m. The conductor of the CS insert coil is the same as that of the ITER-CS coil. The CS insert coil will be installed inside the CS model coil. The conductor performance will be demonstrated on the maximum magnetic flux density of 13 T at the test facility of Japan Atomic Energy Research Institute (JAERI).

Japan Atomic Energy Research Institute (JAERI) has been designing and developing the Central Solenoid (CS) model coil for International Thermonuclear Experimental Reactor (ITER). The CS model coil is composed of two modules and they will be manufactured by United States Home Team and Japanese Home Team. The coil winding method is two-conductors-in-hand and the coil which has an inner diameter of 1.6 m and an outer diameter of 3.6 m, produces a maximum field of 13 T. The coil will be tested in the JAERI facility. This paper describes the coil design, manufacturing procedure, stress analysis on the winding pack and AC loss analysis.

The [Nb.sub.3]Sn cable is being fabricated for the Central Solenoid (CS) Model Coil under the ITER Engineering-Design Activity. The cable consists of about 1000 strands whose diameter is 0.81 mm. The design current is 48 kA at a magnetic field of 13T. The 0.6-GJ CS model coil is operated in a pulse mode (0.5T/s). The first trial fabrication of a 100-m dummy cable and a 20-m superconducting cable was completed successfully. The second trial fabrication of a 1000-m dummy cable was performed to establish the stable manufacturing procedure in January, 1995. We measured the AC losses of the full-sized conductor and could determine the cable coupling time constant. We analyzed the heat generation of the CS model coil and calculated the temperature rise of the cable for the model coil.

Critical current of [Nb.sub.3]Al is less sensitive to strain than [Nb.sub.3]Sn. This characteristic makes a React-and-Wind method applicable in a large dimension coil. By applying the React-and-Wind method for Toloidal Field (TF) coil, technical difficulties in transfer of the conductor after reaction are eliminated and construction cost of magnet system can be reduced in comparison with a Wind-React-Insulate-Transfer method. Therefore, the [Nb.sub.3]Al conductor has large potential as candidate for the TF conductor. The experiment of a 60 kA-12.5T [Nb.sub.3]Al Insert is projected to demonstrate applicability of the React-and-Wind method with the [Nb.sub.3]Al conductor. The React-and-Wind method will be employed in the winding and 0.4% bending strain will be applied to the conductor. The major characteristics of the [Nb.sub.3]Al Insert are reported in this paper.

An 10-kA superconducting coil wound from 108-strand Nb3Al cable-in-conduit conductors was tested at Japan's Atomic Energy Research Institute. The coil, which has a conductor length of 100 m. and a titanium conduit, was shown to have a maximum flux density of 10 T at a transport current of 5.5 kA and a background field of 7.5 T. During single charge operation, it has a maximum flux density of 4.5 T at 10 kA.

Two 40-kA cable-in-conduit conductor wound from (NbTi)3Sn strands and a titanium conduit were developed by Japan's Atomic Energy Research Institute for the central solenoid of a fusion reactor. Tests were also carried out to determine their superconducting behavior. According to results, the two conductors are characterized by high residual resistivity ratio, the absence of ramp rate limits and a temperature margin higher than two kelvin at 13 T and 40 kA.

Superconducting Nb3Al/Cu multifilamentary strands were been prepared according to International Thermonuclear Experimental Reactor specifications for fusion magnets. The strands, which were fabricated using the jelly roll method, have a critical current density of 800 A/mm2. at 12 T and 4.2 K and high tensile strain tolerance. Subsequently, a 1,1,52-strand Nb3Al cable-in-conduit conductor was also developed and tested.

The authors propose a technique for computerized simulation and tangency of gears provided with real tooth surfaces. The deviations of real tooth surfaces from the theoretical ones are caused by the distortion of surfaces during the heat treatment and lapping. The main ideas of the proposed technique are as follows: (i) The gear real tooth surface is represented by a sum of two vector functions that determine the theoretical tooth surface and the deviations of the real surface from the theoretical one, respectively. (ii) Both vector functions mentioned above are represented in terms of the same Gaussian surface coordinates (the Gaussian coordinates of the theoretical surface). (iii) The deviations of the real surface are initially determined numerically using the data of surface coordinate measurements. The analytical representation of the vector function of deviations is based on the interpolation of a numerically given vector function by a bi-cubic spline. The interpolation provides a relatively high precision because it is accomplished for the surface of small deviations but not for the whole real surface. (iv) The computerized simulation of meshing and tangency of gears with real tooth surfaces is based on the algorithm that describes the conditions of continuous tangency of real tooth surfaces. The proposed approach is illustrated with application to the hypoid gear drive with real tooth surfaces. The data of surface deviations have been determined experimentally at the Nissan Motor Co.

A 40-kA [Nb.sub.3]Al cable-in-conduit conductor has been developed for the toroidal field coils of fusion reactors, because [Nb.sub.3]Al has excellent mechanical performance. This conductor consists of 405 copper-stabilized multifilamentary strands inserted into a CuNi circular conduit. The [Nb.sub.3]Al strands are fabricated by the Jelly-roll process with a diameter of 1.22 mm. This conductor could be operated up to a current of 46 kA at an external field of 11.2 T. Accordingly, [Nb.sub.3]Al promises to soon become a useful superconductor for large-scale high-field applications, such as fusion machines.

The effect of cyclic pulsed operation on the coil performance was studied from the electrical and mechanical points of view in the second experiment of the [Nb.sub.3]Sn Demo Poloidal Coil (DPC-EX). Current sharing temperatures, ac losses, displacements, and strains were measured before and after cyclic pulsed operation, which consisted of about 350 cycles. No degradation of the electrical and mechanical performance of the DPC-EX was observed in the range of these cycles.

A high field magnet system, up to 19 tesla at 1.8K, with magnet bore of 75mm was developed. The magnet consists of [Nb.sub.3]Sn solenoids (3 sections) and NbTi solenoids (2 sections). A Liquid helium vessel is divided into two parts (4.2K upper part and 1.8K lower part) by a fiberglass reinforced plastics separator. The central field is 17 tesla at 4.2K with normal liquid helium and 19 tesla at 1.8K with pressurized superfluid helium. This magnet can be operated in persistent mode and the field stability at that time is less than 10ppm/hour. The field homogeneity is better than 0.1% at 50 mm sphere volume. The stored energy is about 3MJ. A small refrigerator was installed on the top flange of the cryostat to reduce the evaporation rate of liquid helium and to maintain the superconducting magnet at low temperature while pausing. This system is used for the measurement of critical current and other physical properties of superconducting wire and other materials such as high Tc superconductors.

Japan Atomic Energy Research Institute (JAERI) has been developing 13-T, 40-kA conductors for the ITER Central Solenoid Scalable Model Coil. The conductors are composed of high performance [(NbTi).sub.3]Sn strands and titanium conduit. In this development work, 15-km length strand fabrication from a 100-kg billet, chrome plating, cabling of 675 or 768 strands, jacketing of titanium conduit, and so on were conducted by two mass production lines. In this paper, several test results are reported such as critical current measurements of full-scale conductors and AC loss measurements of sub-scale conductors.

The Japan Atomic Energy Research Institute (JAERI) has developed the Advanced Disk and the Hollow Monolithic conductors for the FER/ITER Toroidal Field coils. The Advanced Disk conductor is a Cable-in-Conduit conductor which consists of 324 Nb3Sn strands. The Hollow monolithic conductor has hollow cooling channels and 23 Nb3Sn strands. The JA-FENIX sample consists of a pair of straight legs: one leg is the Advanced disk conductor and another is the Hollow Monolithic one. The FENIX facility at the Lawrence Livermore National Laboratory (LLNL) can provide a magnetic field up to 13T on a sample conductor of over 40cm-length. The performance test of the JA-sample was carried out in Autumn 1992. The critical current, the current sharing temperature, and the stability margin of each conductor were measured in this test. These results are presented and discussed.

Multifilamentary [(Nb, Ti).sub.3]Sn superconducting wires with reinforcing stabilizer of CuNb composite, CuNb/[(Nb, Ti).sub.3]Sn, were developed. The outstanding point is that the 0.2 % proof stress at 4.2 K in CuNb/[(Nb, Ti).sub.3]Sn was extremely improved to 320 MPa even after the heat treatment at 670 [degrees] C for 192 hours, which is 1.8 times higher than that in ordinary Cu/[(Nb, Ti).sub.3]Sn. The overall [J.sub.c] value in CuNb/[(Nb, Ti).sub.3]Sn was obtained to be 110 A/[mm.sup.2] at 16 T and 4.2 K. These results show that the bronze processed multifilamentary [(Nb, Ti).sub.3]Sn superconducting wire with CuNb reinforcing stabilizer is actually employable for a high field superconducting magnet.

The development of a multifilamentary Nb3Sn wire containing a copper niobium (CuNb) stabilizer is reported. Fabricated via the bronze process, the Nb3Sn/CuNb wire's electrical characteristics at 23 T and 4.2 K include a residual resistance ratio of 20 and a 0.2-micro-ohm.cm magnetoresistance. Its mechanical strength and superconducting properties suggest that it is suitable for use in high-field superconducting magnets

Experimental tests have been conducted by the Japan Atomic Energy Research Institute to characterize the performance of its 30-kA Demo Poloidal Coils. The coils, whose windings are formvar-coated niobium titanium cable-in-conduit conductors, were tested extensively to evaluate their stability margin and current distribution. The results were then used to modify their design and construct new 30-kA conductors.

The Demo Poloidal Coil (DPC) program at the Japan Atomic Energy Research Institute aims to advance superconducting technology to develop superconducting coils for fusion experimental devices. So far, it has designed and tested four kA-class Nb3Sn coils with a 1-m bore. These are the DPC-EX, US-DPC, DPC-TJ and the Toroidal Model Pancake. A report on their operating performance and ac loss measurements is presented.

The Toroidal Model Pancake is a test coil that was constructed by the Japan Atomic Energy Research Institute for fusion reactor studies. Built of a 90-m hollow cooling monolithic conductors, it has an 1-m bore and a 1.5-m outer diameter. It was subjected to ac loss measurements which found the effective diameter of its (NbTi)3Sn and niobium titanium conductors to be 4 micrometer and 39 micrometer, respectively.

The characterization of the Toroidal Model Pancake (TMP) is presented. The TMP is a superconducting coil constructed by the Japan Atomic Energy Research Institute for fusion reactor studies. Built of hollow cooling monolithic superconductors, it begun testing in Aug 1992. Its performance is described along with cooldown, pressure drop, stability and mechanical issues.

Japan Atomic Energy Research Institute has a program for the development of (NbTi)3Sn conductors for the International Thermonuclear Experimental Reactor's center solenoidal coil. Its goals are to manufacture a superconducting strand with current densities in the range of 800 A/mm2 and low ac losses. Currently, their research has concentrated on quantifying the performance of conductor samples fabricated by the bronze process, niobium tube approach and the internal tin diffusion method.

The Demo Poloidal Coil-TJ is a superconducting coil for a superconducting fusion magnet. Developed by Toshiba and the Japan Atomic Energy Research Institute, the force-cooled coil is designed for high-magnetic-field and high-current-density operation and is built of Nb3Sn cable-in-conduit conductors. It is electromagnetically and mechanically stable, as borne out by quenching tests and measurements of its critical current and current sharing temperature.

The development of Nb3Al cable-in-conduit conductors for International Thermonuclear Experimental Reactor magnets is presented. It gives a characterization of the conductors manufactured for 11.2-T operation obtained from tests on critical current density and mechanical strength. The fabricated conductors, with a current rating of 40 kA, are made of 324 Nb3Al filaments inside a copper-nickel conduit.

The effectiveness of quasi-graded superlattices at the heterointerfaces in reducing the series resistance of a distributed Bragg reflector was investigated. The results showed that the superlattices allowed a low series resistance distributed Bragg reflector to be obtained without any trade-off in reflectivity. Increased tunneling current resulted in decreased resistance.