Core-suppressed AC loss and strand-moderated contact resistance in a Nb3Sn rutherford cable

摘要

Calorimetric measurements of AC loss and henceinterstrand contact resistance (ICR), have been performed on twotypes of Rutherford cable wound with unplated Nb3Sn strand. Oneof the cable types was furnished with a thin core of AISI 316Lstainless steel and the other was left uncored. The cables weresubjected to pressures of 5, 10, and 20 MPa, respectively, duringreaction heat treatment (RHT), and to 100 MPa duringmeasurement. AC loss was measured at 4.2 K in sinusoidalmagnetic fields of amplitudes 200 and 400 mT at frequencies of 5to 90 mHz both with and without the presence of DC bias fields ofup to 1 T. The magnetic fields were applied both parallel andperpendicular to the face of the cable. For the cored cables ICRwas relatively high (78μΩ).Loss and contact resistance wererelatively independent of RHT pressure within the range measured.The contact resistance of the uncored cables were also RHT-pressure independent, however, the absolute values of ICR weremuch lower, being about 2.7 μΩ with a 1 T background field, andvery much smaller in the absence of a background field. Thebackground-field dependence was shown to be due to the presenceof an unreacted Nb barrier which enveloped the strand just belowthe external Cu stabilizer and thereby provided very low resistancecoupling paths at small bias fields. The relative roles of strand andcable designs in the determination of interstrand losses arediscussed. It is concluded that a low-loss Nb3Sn Rutherford cablehas been achieved through the use of a metallic-alloy core.