Recent results from R&D; on superconductors at CRPP
Prototype conductors for the ITER magnets have been tested extensively in the SULTAN facility at CRPP in the last decade. The in-depth characterization of the high current carrying conductors provided a valuable feedback in the design, with performance optimization and cost reduction. From the transient stability results on full size, short length conductor samples, the temperature margin required to withstand the plasma disruption has been found to be much smaller than originally assumed. A comparison between two specially designed sub-size conductors (the SeCRETS experiment) showed that the copper fraction in the superconducting Nb3Sn composite can be reduced without affecting the stability, leading to a substantial reduction of the overall amount of superconducting composite to be procured for the ITER magnets. The ac loss measurements carried out over a broad range of ac field frequency, brought evidence of two regimes of losses, complementing the test results of the ITER model coils and indicating that the correct eddy currents loss to be retained in the design for plasma disruption and initiation is much smaller than the value extrapolated from the slow charge of the model coils. The impact of the coolant speed on the stability behaviour of NbTi and Nb3Sn cable-in-conduit has been observed both in transient field and dc experiments, leading to the conclusion that the assumption of a constant value for the heat exchange coefficient is inadequate in the design criteria.