Test Results of Three Poloidal Field Superconducting Samples in SULTAN

Superconductors for the ITER Poloidal Field Coils are large cable-in-conduit conductors (CICC) made of NbTi strands encased in a round-in-square stainless steel jacket. Three prototype conductor sections for poloidal field coils PF1/6, PF2/3/4 and PF5 have been fabricated in collaboration of the domestic RF, CN and EU agencies and tested in SULTAN Test Facility at the nominal operating conditions. The test aimed to characterize the DC and AC behavior of the conductors. The DC test was focused on the current sharing temperature (T-cs) at the nominal operating current and nominal operating background field. The take-off electric field at the nominal Helium mass flow rate was investigated versus the cable current density over a broad range of field and temperature. The AC loss measurement was performed before any electromagnetic loading and after a number of load cycles in order to define the impact of cyclic loads on the coupling currents constant of the cable. From the test results in SULTAN test facility, the margins in normal operation and the limits of the operation range of the ITER PF conductors are assessed.

Test Result of a Full-Size Nb3Sn Conductor Developed for the ITER TF Coils

Pierluigi Bruzzone, Boris Stepanov

The Japan Atomic Energy Agency (JAEA) developed ITER TF Nb3Sn conductors that fulfill ITER requirements and has commenced fabricating the conductors to be used in the ITER TF coils. As a qualification of conductor fabrication, two full-size conductor samples, named as JATF4, were prepared and tested by the SULTAN facility at CRPP in Switzerland. Temperature sensors and voltage taps were attached on the three meter-long conductor samples to measure the current sharing temperature (Tcs). Measurements were performed at the beginning of the testing campaign, during cyclic test, and at the end of the campaign following a warm up and cool down. The Tcs values electrically assessed by the agreed procedure at outer magnetic fields of 10.78 T initially were 6.5 K and 6.2 K, and then 6.1 K and 6.0 K at the end of the campaign for each conductor, respectively. These results demonstrate that the conductors have a sufficient Tcs margin to satisfy the ITER TF conductor criterion of 5.7 K, and conductor fabrication is qualified. Details of the test results are presented and discussed.

2011

Prospects for the use of high-T-c superconductors in fusion magnets and options for their test in SULTAN

Pierluigi Bruzzone, Stephen Alfred March, Boris Stepanov, Davide Uglietti, Rainer Wesche

In the last few years, the critical current densities of long commercially available REBa2Cu3O7-x (RE-123, where RE represents Y or a rare earth element) coated conductors have reached values of 250 A/cm-width at 77K and zero applied field. Even higher values of 600 A/cm-w (77 K, B = 0) have been demonstrated in shorter lengths. The attractive features of the use of these high-T-c superconductors (HTS) are operation temperatures above 20K and/or magnetic fields higher than those envisaged for the ITER TF coils. Possible operation conditions for HTS fusion magnets have been studied taking into consideration the possible further improvements of RE-123 coated conductors. Investigations of stability and quench behavior indicate that stability is not a problem, whereas quench detection and protection need attention. Because of the high currents necessary for fusion magnets, many tapes need to be assembled into a transposed conductor. The qualification of HTS conductors for fusion magnets would require their test at magnetic fields of 11 land currents well above 10 kA. The possibilities to test straight HIS conductor samples in SULTAN have been considered. For a test at 4.5 K, only the development of a low resistance joint between the HTS conductor under test and the NbTi transformer of SULTAN would be necessary. Tests up to 20K would require that the HTS sample is connected with the NbTi transformer by a conduction-cooled HTS bus bar of large thermal resistance similar to the HIS module of a current lead. HIS conductor tests at temperatures around 50K would be possible with modified cryogenics. (C) 2013 Elsevier B.V. All rights reserved.

Elsevier Science Sa2013

DC performance, AC loss and transient field stability of five medium size NbTi cable-in-conduit conductors with parametric variations

Pierluigi Bruzzone, Boris Stepanov, Martin Vogel, Rainer Wesche

Five medium size NbTi cable-in-conduit conductors with parametric variations in the cable layout were fabricated of three different strands to investigate their DC performance, AC loss behaviour and transient stability by means of the SULTAN facility. A comparison of measured strand data and the cable performances at the same background field indicates that the current carrying capacity of the conductors is limited by the total magnetic field on the high field side. Due to the self-field contribution the total magnetic field on the high field side is considerably larger than the background field at high currents. The take-off electric fields were found to decrease with increasing quench currents, resulting in sudden take-offs for large overall current densities. Effective self-field factors are used to describe the DC performance in the current range, where the critical current and the current sharing temperature are accessible. The quench behaviour of the conductors is discussed in the framework of a model based on peak-field-induced quenches. Differences in the DC performance of the conductors are related to the variation in the transverse resistance determining the ability of the conductors to redistribute the current in the case of a current imbalance originated at the joints. This aspect was studied in more detail by modifying one of the joints allowing a defined number of subcables to be disconnected. The voltage-current characteristics of strands and cable-in-conduit conductors are compared. The reasons for cable n values deviating from the strand n values are discussed. Moreover, the effect of different transverse resistances on the AC loss behaviour and the transient field stability was investigated. Ni coating of the strands was found to be sufficient to eliminate the interstrand coupling current loss. Thus, additional subcable wraps provided no significant further loss reduction. (c) 2005 Elsevier Ltd. All rights reserved.

2005

DC performance, AC loss and transient field stability of five medium size NbTi cable-in-conduit conductors with parametric variations

Pierluigi Bruzzone, Boris Stepanov, Martin Vogel, Rainer Wesche

2005