Core-suppressed AC loss and strand-moderated contact resistance in a Nb3SnRutherford cable

Calorimetric measurements of AC loss and hence interstrand contact resistan ce (ICR), have been performed on two types of Rutherford cable wound with u nplated Nb3Sn strand. One of the cable types was furnished with a thin core of AISI 316L stainless steel and the other was left uncored, The cables we re subjected to pressures of 5, 10, and 20 MPa, respectively, during reacti on heat treatment (RHT), and to 100 MPa during measurement. AC loss was mea sured at 4.2 K in sinusoidal magnetic fields of amplitudes 200 and 400 mT a t frequencies of 5 to 90 mHz both with and without the presence of DC bias fields of up to 1 T. The magnetic fields were applied both parallel and per pendicular to the face of the cable. For the cored cables ICR was relativel y high ( approximate to 78 mu Omega). Loss and contact resistance were rela tively independent of RHT pressure within the range measured. The contact r esistance of the uncored cables were also RHT-pressure independent, however , the absolute values of ICR were much lower, being about 2.7 mu Omega with a 1 T background field, and very much smaller in the absence of a backgrou nd field. The background-field dependence was shown to be due to the presen ce of an unreacted Nb barrier which enveloped the strand just below the ext ernal Cu stabilizer and thereby provided very low resistance coupling paths at small bias fields. The relative roles of strand and cable designs in th e determination of interstrand losses are discussed. It is concluded that a low-loss Nb3Sn Rutherford cable has been achieved through the use of a met allic-alloy core. (C) 1999 Elsevier Science Ltd. All,rights reserved.