K. Kawano

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.

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.

Recent progress in the demo poloidal coil program

The fabrication of two 30-kA NbTi pulsed coils and one 10-kA Nb/sub 3/Sn coil with a total stored energy of 40 MJ is in progress as a part of the DPC (Demonstration Poloidal Coil) Program. All the Nb-Ti superconducting strands have been fabricated, and their loss time-constant has been measured at 0.32 ms at 7 T, which is well below the initial target of less than 1 ms. A novel winding technique is described for the large current conductor which provides good mechanical contact. >

Experimental results of the Nb/sub 3/Sn demo poloidal coil (DPC-EX)

In order to demonstrate the applicability of a Nb/sub 3/Sn conductor to pulsed poloidal coils for Tokamak fusion machines, the Nb/sub 3/Sn Demo Poloidal Coil (DPC-EX) has been fabricated and tested. DPC-EX, whose inner diameter is 1 m, consists of two double pancakes made by a react-and-wind technique. The coil has a flat cable-in-conduit conductor cooled by forced-flow helium. DPC-EX has been set up in the Demo Poloidal Coil Test Facility (DPCF). In the operation of the coils in series, DPC-EX has been ramped up to 17 kA in 1 s. The magnetic field at this point was 6.7 T, and pulsed operation at 6.7 T/s was thus demonstrated. An average current density of 37.2 A/mm/sup 2/ in the winding was achieved in this operation, and the AC loss of the coil was confirmed to be quite small.

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. >

AC loss results of the Nb/sub 3/Sn Demo Poloidal Coil (DPC-EX)

AC losses in the DPC-EX, whose purpose is to demonstrate the applicability of Nb/sub 3/Sn conductor to poloidal coils for Tokamak fusion machines, were measured, and the results were analyzed. The coil was fabricated with a Nb/sub 3/Sn cable-in-conduit conductor and has a 1 m inner diameter. The AC loss was 9.4 kW for the pulse operation of a 0-17 kA-0 cycle with a ramp time of 1 s, corresponding to a 6.7-T maximum field and a 6.7-T/s pulse rate. It was 0.14% of the magnetic stored energy. The effective Nb/sub 3/Sn filament diameter was estimated as 32 mu m and the effective time constant of the coupling current within the strand was calculated as 2 ms on the assumption that coupling current between strands is negligible. The limitation of coil current due to AC losses is discussed. >

Thermal design and verification tests of the Nb-Ti demo poloidal coils (DPC-U1, U2)

For the development of a 30-MJ, 7-T/s pulsed coil, a 30-kA cable-in-conduit conductor with low pulsed loss was designed and fabricated. The Japan Atomic Energy Research Institute performed verification tests to measure the temperature increase when a high-energy disturbance of 300 mJ/cc-strand is put into the superconducting strands and also to measure the stability margin of the conductor, which is increased by a factor of 1.65 when the He flow rate is increased from 0 to 1.0 g/s at the nominal current under 7 T. A possible mechanism to explain this improvement is discussed. >

Cryogenic system development and helium behavior study for forced-flow superconducting coils

In Japan Atomic Energy Research Institute (JAERI), cryogenic technology development is propelled to aim at realization of superconducting coil system for fusion experimental reactor (FER). For this purpose, forced-cooling technology which is one of attractive cooling methods and is expected to use for one of large superconducting coils for fusion is being investigated according to the cryogenic technology development program shown in Fig. 1. JAERI has already constructed and tested three forced-flow generating facilities which are named as forced flow generator (FFG), segment test facility (STF) and forced flow test facility (FFTF). The forced flow generator (FFG) which can provide supercritical helium up to 3 g/s with 8 atm and 4.5 K was firstly fabricated for fundamental investigation of forced-cooling coils and coolant. As the second step, STF and FFTF were constructed in order to investigate coolant, supercritical helium, control technique combined with the helium liquefier/refrigerator. They are designed to have the capacities of flow rate up to 20 g/s and 60 g/s with 15 atm and 4.4 K by adding supercritical heat exchanger to the existing 350-l/h and 1.2-kW helium cryogenic system. Using these facilities, several forced-cooled superconducting coils with cable-in-conduit conductor were tested and the stability characteristics and supercritical helium behavior in the conductor were measured. This paper describes design concept and tested performances for the forced flow facilities, and pressure rise Characteristics of supercritical helium in cable-in-conduit conductors.

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. >

Performance test results of cryogenic pump system for Demonstration Poloidal Coil

The system, composed of a circulation pump and a cold compressor, is designed to produce supercritical helium with a mass flow rate of 350 g/sec at 10 bar below 4 K in normal operation. The circulation pump uses a reciprocating-pump design with double-acting bellows. The cold compressor uses a centrifugal compressor design with dynamic gas bearings. In performance tests using real cryogenic pumps for the Japan Atomic Energy Research Institute Demonstration Poloidal Coil program, it was found that the measured maximum flow rate is around 680 g/sec at a pressure head of 1.1 bar with adiabatic compression efficiency of more than 60%. >