N. Koizumi

Construction of ITER common test facility for CS model coil

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 (50 kA and 60 kA) and two JT-60 pulsed power supplies (50 kA, /spl plusmn/4.5 kV and /spl plusmn/40 kA, /spl plusmn/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.

Critical current measurements using 13-T split coils and 100-kA superconducting transformer (for FER)

A description is given of a large scale superconductor test facility composed of a 13-T magnetic field and a 100-kA sample current. A superconductor transformer with a 100-kA secondary conductor was fabricated as a current amplifier in order to supply the 100-kA sample current. Superconducting split coils with 100-mm clear bore diameter were fabricated, and a 13-T available field was generated by these coils. Both the 100-kA superconducting transformer and the 13-T superconducting split coils were installed in a 2-m-diameter FRP dewar for the purpose of testing large-scale superconductors. A description is given of the performance of the 100-kA superconducting transformer and the 13-T superconducting split coils as well as the results from critical current measurements of prototype conductors for toroidal coils.

Design and fabrication of superconducting cables for ITER central solenoid model coil

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 13 T. The 0.6-GJ CS model coil is operated in a pulse mode (0.5 T/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. The authors measured the AC losses of the full-sized conductor and could determine the cable coupling time constant. They analyzed the heat generation of the CS model coil and calculated the temperature rise of the cable for the model coil.

Design consideration of the ITER-TF coil with a react-and-wind technique using Nb/sub 3/Al conductor

The ITER-TF coil requires a generation of 12.5 T in a size of 12 m/spl times/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%. I/sub c/ 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.

Design of the Nb/sub 3/Al insert to be tested in ITER central solenoid 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-rind method for toroidal 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-12.5 T 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.

Design of the CS insert coil [ITER superconducting coils]

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 underway 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 1.5 m. 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).

Development of 240 mm bore-13 T superconducting coil for large scale conductor testing

A 240-mm-bore high-field superconducting coil was designed, fabricated, and tested. This coil is planned as a test facility for the development of large-scale superconductors for fusion machines. Tests were performed in a 4.2 K bath, and the designed magnetic flux density of 13.0 T was obtained in the center of its bore. The maximum magnetic flux density on the coil was 13.9 T; the average current density was 101 A/mm/sup 2/; the stored energy was 4.8 MJ; and the charging time was 18.5 minutes. This coil has served as a reliable conductor test facility since the first achievement of 13.0 T. >

Development of full-scale conductors for the ITER Central Solenoid Scalable Model Coils

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 an 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. >

Development of hollow cooling monolithic conductor for ITER TF coil

Results of verification tests for the TMC (Test Module Coil)-FF hollow cooling monolithic conductor are presented. With various strands to test the optimal bronze ratio, the critical current of full-scale samples was measured at 13 T and 4.2 K. The maximum critical current density is 404 A/mm/sup 2/, which is smaller than the requirement of over 500 A/mm/sup 2/ at 12 T. There is no degradation of the critical current of a full size conductor compared with the same sample before cabling. AC losses of the conductor were measured in parallel and perpendicular fields. The results of the time constant measurements are larger than the calculated values in each direction. The stability margin of the full size conductor is 40 mJ/cc-metal at the nominal point, assuming long length disturbance. This result is estimated from experimental results for a reduced size conductor and from thermal analysis. The heat generation of the joint between Nb/sub 3/Sn and Nb-Ti is much smaller than that of nuclear heating. >

Effect of non-uniform current distribution on the stability in Nb-Ti cable-in-conduit superconducting conductor

30kA-NbTi Demo Poloidal Coil (DPC-U) exhibited instability such as the conductor quenches at 40% of the rated current which is still expected conductor critical current, instability was caused by the non-uniform current distribution in the DPC-U conductor whose strands were insulated from each other. To investigate the instability of the DPC-U conductor, a stability experiment of a subsize conductor consisting of 27 strands was performed and the effect of the current imbalance on the stability was investigated. The current imbalance was forcibly established in the conductor using two current sources in this experiment. The experimental results indicate that the stability margin decreases as the current imbalance becomes larger and that the stability margin of the conductor is governed by the stability of the strand with the highest current in the conductor. Also, it is confirmed from the experimental results that the instability of DPC-U has to be attributed to the current imbalance in the conductor.