The US program of poloidal coil development for ITER will focus on the design and fabrication of a model coil for the central solenoid. The recently-tested US-Demonstration Poloidal Coil (US-DPC) is a 2-m-diameter, 30 U, 8 MJ, forced-flow Nb$n solenoid made with a cable-in-conduit conductor using an Incoloy 908 conduit. It is approximately one half the scale of the proposed ITER model coil, and its test results offer several implications for the model coil design. The US-DPC, the first large-scale pulsed magnet made in the US, was built by seven companies under MIT supervision and was tested at the Japan Atomic Energy Research Institute (JAERI) in late 1990. The US-DPC was leak tight; it performed very well in DC tests; it performed well in AC tests, achieving approximately 70 % of its ambitious design goal of 10 T/s to 10 T in a series-connection mode with the JAERI background field coils DPC-U1 and U2. In a single-coil mode, the US-DPC achieved stable ramps ranging from 0.5 T/s to 6.6 T (35 kA) to as high as 19 T/s to 4.0 T (21 U). An unexpected barrier of field or current (or both) versus ramp rate was identified above 23 kA, which appears to be related to short-duration energy disturbances and the "limiting current" of the conductor. This paper describes the design and fabrication of the coil and the applicability of the US-DPC experience and test results to the ITER model poloidal coil.
InaoductionThe niobium-tin superconducting magnets of the International Thermonuclear Experimental Reactor (ITER) represent a substantial fraction of the projected multibillion dollar cost. The enormous cost and sheer size of the machine make reliability and availability of the magnet systems of utmost importance since the time for removal and replacement of a typical magnet is measured in years.[l-2] The US program of poloidal field (PF) coil development will focus on the design and fabrication of a model for the central solenoid (CS) with primary emphasis on component and operational reliability. The PF model will consist of a stack of double pancakes that are approximately two thirds of the CS size, but built using conductor and fabrication techniques specified for the central solenoid.The experimental basis for the model comes from work done in the US, Japan and Europe.[3-51 In particular, the recent Demonstration Poloidal Coil @PC) experiments at JAERI have produced data that add significantly to our knowledge of pulsed superconducting magnets. The US-DPC, the US contribution to the experiment, was approximately one half the diameter of the proposed model coil. It used, however, a Nb3Sn cable that is similar to the one proposed for the model and a conduit material that is identical to it[67]The size of the central solenoid of ITER is unmatched by any existing w S n superconducting magnet and the proposed PF model is approximately one order of magnitude smaller in volume. However, the model is considered a fair engineering approximation because both w i l l be modular and characterization of the modules is thought to be s...
