Effect of mechanical deformation on Nb-Ti filament proximity-effect coupling at the edges of SSC cables

Magnetization as a function of transverse magnetic field and time was measured for short strands extracted from the centers and edges of five Nb-Ti Rutherford cables designed for use in Superconducting Super Collider dipole magnets. The multifilamentary strands all had 6-μm-diameter filaments. Edge samples, which had severe mechanical deformation, showed small magnetic coupling losses at low fields, compared to no coupling losses for underformed center strands. The existence of sharp strand bends at cable edges decreases the interfilament spacing to the order of the coherence length in the normal matrix material, which increases the effective filament diameter and hysteresis loss at low fields. Microscopic studies of the cables´ cross sections confirmed smaller interfilament separations in these samples. Flux creep measurements, represented by the time dependence of magnetization, showed little difference between edge and center samples