Measurements of RRR variation in strands extracted from Nb3Sn-type Rutherford cables

Modem high-J(c) Nb3Sn strands and cables for use in high field accelerator magnets suffer from flux Jump-related instabilities at low magnetic fields. These instabilities are determined by the values of J(c) d(eff), and RRR. It has been postulated that local RRR is a more relevant parameter than average RRR for stability considerations, but the range of RRR values present in a cable has not yet been quantified. Thus, longitudinal variations of RRR were estimated from multiple-tap measurements along the length of strands extracted from mixed strand cables. The cables had either 27 or 28 strands, two different keystone angles, and four different levels of compaction. One type of RRP strand was extracted from each cable, reacted, and then measured. RRR of the straight sections (on the faces) was above 100, while that at the edges of the strand was estimated to be an order of magnitude smaller approximate to 10. Selected regions of the strand with locally depressed RRR were examined by SEM and EDS to check for Sri leakage and examine the type of strand failure present. The implications of these measurements for stability were then discussed.