H. Mukai

Development of high current density, large superconducting coil for fusion machines: the DPC-TJ Program

Abstract A 40 A mm −2 , 24 kA, high rigidity, large forced-cooled, (NbTi) 3 Sn superconducting coil referred to as the DPC-TJ was developed during collaboration between the Japan Atomic Energy Research Institute and Toshiba Corporation. The purpose of the DPC-TJ Program is to demonstrate the realizability of a high average current density with a large coil wound by a large Nb 3 Sn superconductor which meets the requirements of the conductor for the next thermonuclear fusion machine. The DPC-TJ was fabricated as the first coil of the preformed-armour type, which was developed in this programme as a fabrication method that enables us to achieve high rigidity and high current density simultaneously without difficulty. Testing of the DPC-TJ coil was performed successfully and the DPC-TJ Program was completed having accomplished its objectives.

Test results of the DPC-TJ: thermal and hydraulic performance☆

Abstract The thermal and hydraulic test results of the DPC-TJ coil, a 24 kA-40 A mm −2 forced-cooled Nb 3 Sn coil, are presented in this paper. The DPC-TJ coil was installed and tested between the DPC-U1 and U2 coils. The weight of the DPC-TJ coil is 2.8 ton and the total cool-down weight of the coil system is 23 ton. It took ≈ 180 h to cool the coils from room temperature to 20 K. The DPC-TJ coils heat load was 20 W at zero transport current and 40 W at 24 kA, the rated charging state. The pressure drop in the DPC-TJ coil was measured and the obtained value agreed well with that determined by the empirical formula used for the design of the DPC-TJ coil. A.c. losses and inductive losses due to heat input cause a rapid decrease in the helium flow rate at the coil inlet position. This phenomenon was analysed and one of the design standards was derived.

Test results of the DPC-TJ: stability performance

Abstract In this paper the stability test results of the DPC-TJ coil are summarized. The DPC-TJ coil is a cable-in-conduit, forced-flow type, large superconducting coil, cooled by supercritical helium. The stability test was performed using an inductive heating method, and the dependences of the stability margins on the operating current and on the duration of heating were investigated. The relation between heating power and the take-off time, defined as the time from the start of heating until the appearance of normalcy in the conductor, was also studied. The main results are as follows: the so-called limiting currents were not obvious with the present test conditions; the influence of the duration of heating on the stability margin was small; and the heating power was inversely proportional to the square root of the take-off time, up to ≈ 20 ms.

Test results of the DPC-TJ: electromagnetic performance☆

Abstract The DPC-TJ coil experiment was successfully carried out at the Japan Atomic Research Institute (JAERI) in 1991. This coil was developed by Toshiba and JAERI in collaboration to demonstrate the realization of superconducting coils for fusion with a high average current density of 40 A mm −2 . The DPC-TJ coil was charged up to its rated current of 24 kA (40 A mm −2 ) at 7.6 T without quench in the DPC test facility. Thereafter electromagnetic performance was tested by measuring I c and T cs values, and the critical current at 12 T was estimated at 41 kA. Many electromagnetic results were obtained, which are necessary for the design of future fusion machines such as the International Thermonuclear Experimental Reactor (ITER).

TEST RESULTS OF THE DPC-TJ, A 24 kA-40 A/mm2SUPERCONDUCTING TEST COIL FOR FUSION MACHINES

A high–current–density large forced–cooled (NbTi)3Sn superconducting test coil for fusion machines named DPC–TJ was developed and tested. This test coil is the first coil adopting the new winding concept which enables high coil-rigidity together with high current–density. The coil was investigated in detail, and its designed rated state of 24 kA–12 T–40 A/mm2was confirmed to be obtainable by the equivalent condition test. Through this development work, it was verified that superconducting coils for future large fusion machines could be designed with high current-density.

Charging test results of the DPC-TJ, a high-current-density large superconducting coil for fusion machines

The authors describe the electromagnetic results and the quench phenomena of the DPC-TJ large cable-in-conduit Nb/sub 3/Sn coil experiment which took place in the summer of 1991. The DPC-TJ coil was developed by Toshiba and JAERI in collaboration to demonstrate the realization of (NbTi)/sub 3/Sn superconducting coils for fusion with high average current density of 40 A/mm/sup 2/. The coil was charged up to its rated current of 24 kA (40 A/mm/sup 2/) at 7.6 T without quench in the DPC test facility. Thereafter, the electromagnetic performance was tested by measuring I/sub c/ and T/sub cs/, and the critical current at 12 T was estimated to be 41 kA. The quench phenomena of the DPC-TJ coil were also tested by measuring normal-zone propagation velocity to get the protection design. In these experiments, very slow and very fast propagation were observed. Many other electromagnetic results were also obtained, which are necessary for the design of fusion machines such as International Thermonuclear Experimental Reactor.<<ETX>>

Test results of the DPC-TJ: mechanical performance

Abstract The mechanical performance of the DPC-TJ coil was measured during the charge-up test by strain gauges and displacement gauges attached directly to the coil surface. To estimate winding stiffness, expansion tests were performed on a winding model at both 300 and 77 K. The test results obtained with the DPC-TJ coil were compared with calculations obtained by the finite element method (FEM) analysis and expansion test results. Such comparison showed that equivalent Youngs moduli calculated by the FEM were in good agreement with those measured during the charge-up test of the DPC-TJ coil, which had a higher rigidity than the winding model. As a result of the charge-up test, it was demonstrated that the DPC-TJ coil had high rigidity, as designed.

Fabrication of superconductor for the DPC-TJ coil☆

Abstract A forced-cooled superconducting coil (DPC-TJ) was wound with a double walled cable-in-conduit referred to as preformed-armour type C ICC. In this paper, we describe the fabrication of the conductor for the DPC-TJ coil with the first conduit, which plays a role in sealing the supercritical helium from the vacuum. Because the DPC-TJ coil has a high average current density of 40 A mm−2 (12 T,4.2 K) in the winding area, an (NbTi)3Sn strand formed by the Nb tube method was selected, which has a very high critical current density in the non-Cu area. As a result of development work, a strand could be fabricated which met the following requirements: critical current density > 600 A mm−2 at 12 T and residual resistivity ratio (RRR) value > 50. A fabrication line for the cable-in-conduit conductors using the roll-forming method was also developed. Through fabrication of the conductor for the DPC-TJ coil, it was demonstrated that large and long conductors could be fabricated for future fusion reactors.