K. Koizumi

Roughened surface study on japanese test coil for the large coil task

The Japanese test coil for the Large Coil Task utilizes a pool cooling method. In order to get better stabilization in the coil, many different roughened surfaces were investigated. Chemically oxidized Thermo-excel-C surface was selected as the cooling surface for the Japanese LCT conductor. The steady state boiling helium heat transfer characteristics of this surface were measured, and even with the coil simulating long narrow cooling channel its equal area heat flux is more than 1.0 W/cm2. Stability of the Japanese LCT conductor was analyzed using measured data, and the conductor proved to be sufficiently stable.

Domestic test result of the Japanese LCT coil

Japan Atomic Energy Research Institute (JAERI) has been preparing one D shape superconducting coil for the Large Coil Task. This paper describes mainly the results on domestic test which has been successfully carried out with a single test condition in JAERI this year. The main results, which were obtained during the test, are cool-down and warm-up characteristics, superconducting recovery characteristics, discharge characteristics, strain and displacement measurements, and heat load measurements. Before describing the results, the Japanese coil design parameters and the Superconducting Engineering Test Facility for the domestic test are shown in this paper.

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.

Design of the prototype conductors for the Fusion Experimental Reactor

The prototype conductors of the toroidal coil for the Fusion Experimental Reactor have been investigated. Specifications of the conductor are as follows: forced flow cooling; rated current of 30 kA at 12 T and 4.2 K; margin of critical current of 2; current density in winding of 30-40 A/mm/sup 2/; inlet helium at 4.2 K and 4-10 bar; and minimum bending radius of 1.5 m. Three types of conductors were considered as candidates: a test module coil of FF type (hollow cooling type using test module coil Nb/sub 3/Sn conductor techniques); preformed armor type; and advanced disk type. Detailed design parameters and analysis results are given for the three candidate conductors. >

Construction and operation of the cluster test facility

The 20MJ superconducting cluster test facility, which has been under construction for the last two years at Japan Atomic Energy Research Institute (JAERI), was successfully operated in August 1980. Operating design values were achieved without any premature quenching. The fabrication and operation of the facility was the first experience with a superconducting toroidal coil in Japan. The succesful operation of the facility system makes it possible to test a 10T Nb 3 Sn magnet as a Test Module Coil which will be placed in the facility next year. This paper outlines briefly the facility system and describes mainly thermal results and stress results.

Testing of the pool-boiling cooled Japanese LCT coil in the international fusion superconducting magnet test facility

The Japanese LCT coil has successfully achieved the design field of 8 T in the toroidal array of the six LCT coils. In March, 1986, tests of the LCT coils were started following the cooldown of the whole facility. In the single-coil test and design-point test, in which the maximum field was 6.4 T and 8.1 T, respectively, the coil was charged, discharged, and dumped under different conditions. A recovery test and a simulated nuclear heating test were performed to investigate the stability of the coil. Measurements of displacement under the several conditions of electromagnetic load were analyzed to explain the mechanical behavior of the coil. Results obtained in the tests are reported in this paper.

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. >

Development of a forced-cooled superconducting coil with high average current density (DPC-TJ)

A forced-cooled superconducting coil (DPC-TJ) using a double-walled cable-in-conduit, the so-called Performed Armor CICC, has been developed. The DPC-TJ is an advanced coil with an average current density of 40 A/mm/sup 2/, operating current of 24 kA, and field of 12 T. The DPC-TJ coil has several advantages such as mechanical rigidity, negligible degradation of critical current, sound electrical insulation, and excellent winding tolerance compared with a conventional forced-cooled coil. A superconducting strand was developed with the aim of improving the critical current density and resistivity. The resulting Nb-tube-processed (NbTi)/sub 3/Sn strand fulfils the requirement that the critical current density be more than 600 A/mm/sup 2/ at 12 T and the RRR (residual resistivity ratio) be higher than 50. >

Experiment of 10-T, 60-cm-bore Nb 3 Sn test module coil (TMC-1) for the cluster test program

A 60-cm-bore coil wound with a reacted multifilamentary Nb 3 Sn conductor, named as TMC-1, was constructed. A magnetic field of 10.2 T was successfully generated at a current of 6,056 A with a back-up field of 3.3 T from the cluster test coil. The total stored energy was 39 MJ. The strain of the Nb 3 Sn conductor was 0.67 % including a bending strain of 0.54 % during winding. Moreover, a 30-cm-length normal zone, nucleated by heater-input technique in the innermost turn, was recovered to superconducting state at 10 T. This means that a heat flux of conductor cooling surface is more than 1.08 W/cm2. For the manual dump with a decay time of 14 second(B=0.48 T/sec.), the TMC-1 was stable without any damage. The TMC-1, which is pool-cooled at 4.2 K, is constructed as a step of the development of high field toroidal coil in a tokamak fusion machine. From thease results, it is demonstrated that multifilamentary Nb 3 Sn conductor is applicable to large-current and large-size coil.