Single-Strand Excitation for Probing Current Sharing and Parallel Resistance in Cored Nb3Sn Rutherford Cables at 4.2 K and 10 Tesla

A rig was fabricated to test single-strand excitation and current sharing in Nb3 Sn Rutherford Cables. Measurements were performed on 400 mm lengths of a 27-strand, cored cable. In preparation for measurement, the cable was mounted onto a U-shaped holder, reacted for 72-48-50 h at 210-400-665 °C under 20 MPa. Current was injected into a single strand of the cable, and the onset of current sharing was seen above single strand Ic. After the onset of transition, the I-V showed a flat baseline the slope of which gave the transfer resistance to the two neighboring strands. Two cable samples were measured, one of which was reacted in a dilute oxygen atmosphere. The slightly oxidized cable had a R
_∥
of 280 nΩ, whereas the other sample had a R,, was 70 nΩ per lay pitch. Varying I/Ic and a heat pulse from a carbon paste heater was used to turn off successive pairs of neighboring strands, and the resulting current-distribution was measured using voltage taps. These measurements were performed as a screening for cable and cable preparation protocol for larger scale measurements.