AC Loss Measurements in CICC With Different Aspect Ratio

The coupling loss in a cable in conduit conductor (CICC) is strongly influenced by the cable geometry. Beside the cable pattern, twist pitch, wrapping and void fraction, also the aspect ratio has a not negligible role in the loss. In fact, it defines the area crossed by the flux variation and it determines therefore the entity of the coupling current between strands. An AC loss experiment on two Nb₃Sn CICC samples (PITSAM II and PITSAM III) is carried out with a calorimetric method in the SULTAN test facility, in order to investigate the impact of the conductor aspect ratio on the loss. The two conductors, identical for cable pattern, void fraction and characteristics of both superconducting and copper strands, differ only in the aspect ratio, having PITSAM II and PITSAM III a square and a rectangular cross-section respectively. After the DC measurements scheduled in the SULTAN test-procedure (including cyclic load), each sample is tested in a sinusoidal field perpendicular both to the background field and to the conductor axis and generated by a pair of saddle shape coils. The background field during the tests is 2 T while the peak to peak amplitude of the sinusoidal signal is plusmn 0.3 T, with a frequency in the range between 0.2 and 6 Hz. The rectangular PITSAM III is tested in a sinusoidal magnetic field perpendicular first to the wide then to the narrow side of the conductor, so that the loss relative to three different aspect ratios is compared. The relation between loss and aspect ratio is also investigated with reference to the time constants tau and to the shape factor n.