M. Spadoni

Conductor fabrication for the ITER model coils

The Nb/sub 3/Sn cable-in-conduit 40 kA, 13 T conductors proposed for the next generation ITER tokamak are being tested by the construction of a 600 MJ solenoid and a 80 MJ race track coil. The conductors are being manufactured in a world wide collaboration, with task sharing among the four partners of the ITER project. To date, the qualification and /spl sim/20% of the procurement of the Nb/sub 3/Sn strands is complete. Several hundred meters of dummy copper cable and short lengths of superconducting cable are available. The production of jacket sections is advanced and the two jacketing lines are set up for production. The manufacture of 98 tonnes of cable-in-conduit conductors will be completed in autumn 96.

Test results on the first 50 kA NbTi full size sample for the International Thermonuclear Experimental Reactor

Within the framework of the R&D studies for the International Thermonuclear Experimental Reactor (ITER) project, the first full size NbTi conductor sample was fabricated industrially and tested in the SULTAN facility (Villigen, Switzerland). This sample (PF-FSJS), which is relevant to the poloidal field coils of ITER, is composed of two parallel straight bars of conductor, connected at the bottom through a joint designed according to the CEA twin-box concept. The two conductor legs are identical except for the use of different strands: a nickel plated NbTi strand with a pure copper matrix in one leg, and a bare NbTi strand with a copper matrix and internal CuNi barrier in the other leg. The two conductors and the joint were extensively tested as regards DC and AC properties. This paper reports on the test results and analysis, stressing the differences between the two conductor legs and discussing the impact of the test results on the ITER design criteria for the conductor and joint. While joint DC resistance, conductors and joint AC losses fulfilled the ITER requirements, neither conductor could reach its current sharing temperature at relevant ITER currents, due to instabilities. Although the drop in temperature is slight for the CuNi strand cable, it is more significant for the Ni plated strand cable.

Design and manufacture of a prototype NbTi full-size joint sample for the ITER poloidal field coils

Abstract The design of the poloidal field (PF) coils of the International Thermonuclear Experimental Reactor (ITER) relies on the use of 45 kA NbTi cable-in-conduit conductors. An R&D programme is carried out jointly between CEA and ENEA to acquire knowledge on the behaviour of such conductors. In addition to the manufacture and tests of two subsize joint samples at CEA Cadarache, the design of a poloidal field full-size-joint sample (PF-FSJS) has been carried out. This sample is composed of two conductor legs made of stainless steel-jacketed NbTi full size cables, of a lower joint built according to the “twin box” concept developed at CEA, and of two upper terminals to be connected to the facility current leads. A description of the sample design, the techniques used for the different manufacturing steps of the conductor legs, the terminations and the assembly is related. This prototype sample will be tested in the Sultan test facility at Villigen (Switzerland) and will be a model for the manufacture of joints for the PF coils.

Development of high-current high-field conductors in Europe for fusion application

In the framework of the preparation for the realization of the international thermonuclear experimental reactor (ITER), the construction and test of relevant models of seven different parts of the reactor was decided. Two of them are related to the superconducting coils: the toroidal field model coil (TFMC) and the central solenoid model coil (CSMC). For these superconducting coils, due to the expected high values of the current (≥60 kA) and voltage (≥5 kV with respect to the ground) the adopted technology was that of cable in conduit conductor (CICC). Until recently, little experience of this technology existed. Therefore, an extensive research and development programme has been carried out, in the last 10 years, by the ITER partners and particularly in Europe, to design, industrialize and test these large conductors and their joints. The EURATOM associations CEA and ENEA played a leading part in this phase. The CICC concept is described and the results of the developments are presented. About 7 km of conductors were manufactured in the industry and for that more than 10 tonnes of Nb3Sn strands were produced in Europe. In this large programme, Europe is particularly in charge of the TFMC, which will be tested this summer at Forschung Zentrum Karlsruhe (Germany). In the framework of this programme, three full size conductors and joint samples were tested at the European Sultan test facility (Centre de Recherches de Physique des Plasmas, Villigen, Switzerland), to validate the technological choices and check that the ITER specifications were met. The results of these tests are presented in detail. Starting from the strand critical properties, the conductors made of about 1000 strands did reach their expected performance. The joints of these large conductors are very special and delicate components. Their behaviour was quite successful and the joint resistance of these samples (of the order of 1 nΩ) was well within the specifications.

The ITER Toroidal Field Model Coil (TFMC)

Abstract The TF coils for ITER (ITER, Final Design Report, December 1997) will use the concept of a circular thin walled Nb3Sn cable in conduit superconductor completely enclosed in an insulated groove in steel plates to form the coil pancakes. These are then stacked together to form the winding pack supported by a steel case. The concept is being demonstrated by the fabrication of a TFMC (E. Salpietro et al., Construction of a Toroidal Field Model Coil (TFMC) for ITER, MT-15 Fifteenth International Conference on Magnet Technology, Oct 20–24, 1997, Beijing, China; R. Maix et al., Manufacture of the ITER TF model coil (TMFC), Poster P1-217) with a bore of 1.4×2.5 m, a peak field of 8.77 T and a total current of 7.8 MAT. The coil will be tested during 1999 in the TOSKA facility at FZK, Karlsruhe, using the EURATOM LCT coil to provide an external field system. The objectives of the TFMC are as follows: 1. to develop and verify the full scale TF coil manufacturing techniques, in particular the following features: ◦ plate manufacturing (forming the grooves); ◦ fitting the conductor in the groove after heat treatment and insulation (i.e. predictable geometry change); ◦ closing the groove with a cover plate and plate insulation; ◦ fitting the winding into the case, gap filling and case closure; 2. to establish realistic manufacturing tolerances; 3. to bench-mark methods for the ITER TF coil acceptance tests, including insulation and impregnation process; 4. to obtain information on the coil’s mechanical behaviour, operating margins and in-service monitoring techniques, particularly for the insulation quality over fatigue cycles.

Direct measurement of the AC loss of an ITER relevant coil

Abstract In the ENEA Frascati Laboratory, an ITER relevant coil is being tested in pulsed regime. One item of the testing program is the search for possible ramp rate limitations. The range explored (up to 3.2 T/s) covers amply the ITER Central Solenoid operating regime (0.5–1 T/s). An interesting outcome of these tests is that repeated run sets, performed in similar conditions, show an increasing value of the ramp rate that produces a quench. This behaviour is attributed to a continuous decrease of the value of the AC loss constant nτ, due to the increase of the cable transversal resistivity. An explanation on the basis of a `classical training was also considered, but for a number of reasons reported in the paper, it was discarded. Direct measurements of the AC loss on the whole coil confirm that the original value of nτ (140 ms), as measured on a `virgin piece of conductor, has gone below 40 ms. The measurements are made difficult by the presence of a heavy mechanical structure and of a background coil. The techniques applied and the results are reported in detail.

Conceptual design of the ITER TF model coil

The aims of the toroidal field (TF) model coil are to test the manufacturing feasibility of the ITER TF magnet concepts, to assess the reliability of the fully integrated system by dedicated testing and to qualify the quality assurance and the testing methods. The 3.8 m long racetrack shaped TFMC will be tested in the TOSKA facility at Karlsruhe in a configuration using the Euratom LCT Coil to provide in-plane and out-of-plane loads, relevant to the ITER coils.

Status report on the 12 T split coil test facility SULTAN (for NET magnets)

The third phase of upgrading of the superconductor test facility SULTAN into a split coil system (SULTAN III) is in progress. SULTAN III consists of two coil packages, each containing three concentrically mounted superconducting solenoids. Together they will produce a field of nearly 12 T between the two coil packages, inside a solenoid bore of 58 cm. The outermost 6 T coils have NbTi conductors, whereas the inner 9 T and 12 T coils are made of A-15 cables. All Nb/sub 3/Sn coils are manufactured by the react-and-wind technique. The split coil arrangement, in connection with a sophisticated sample insert containing a 50 kA superconducting transformer, will allow testing of short samples of high-current-carrying superconductors, e.g. for fusion applications. The sample insert was designed to allow changing the samples within a few hours without warming up the whole magnet system. The authors discuss the present status and potential of SULTAN III. >

Status report on the forced flow high field test facility SULTAN

The construction of the Test Facility SULTAN - a common action of three European laboratories: ENEA (I-Frascati), ECN (NL-Petten) and SIN (CH-Villigen) is near completion. In this paper the status of the contributions of the different partners is described: (a) The SIN part of the facility, the cryogenic system the current leads, the power supplies and the data acquisition system has been put into operation. Results of these tests are presented. (b) The background field will be generated by two concentric solenoids. The ENEA contribution is concerned with the realization of the outer solenoid. This coil, which has been recently completed, will provide a 6 T field in the useful region, the remaining 2 T being supplied by the coaxial ECN insert coil. Details of the design, winding technique, hydraulic circuitry as well as instrumentation of both coils will be given and discussed. In addition the future upgrading to 12 T is outlined.

Testing of industrial Nb/sub 3/Sn strands for high field fusion magnets

A systematic test of I/sub c/, hysteresis loss and RRR on advanced Nb/sub 3/Sn strands from industrial production has been carried out at European Laboratories, highlighting the reproducibility of the test results, the calibration, the accuracy, as well as the scattering among specimens of the same type. Practical recommendations are drawn for reliable acceptance testing of large series production of Nb/sub 3/Sn strands. >