AC loss and contact resistance in copper-stabilized Nb3Al Rutherford cables with and without a stainless steel core

Calorimetric measurements of AC loss and hence interstrand contact resistan ce (ICR), were measured on three samples of Rutherford cable wound with Cu- stabilized jelly-roll type unplated Nb3Al strand. One of the cable types wa s furnished with a thin core of AISI 316L stainless steel and the other two were both uncored but insulated in different ways. The cables were subject ed to a room-temperature-applied uniaxial pressure of 12 MPa that was maint ained during the reaction heat treatment (RHT), then vacuum impregnated wit h CTD lot epoxy, and repressurized to 100 MPa during AC-loss measurement. T he measurements were performed at 4.2 K in a sinusoidal field of amplitude 400 mT at frequencies of 1 to 90 mHz (no DC-bias field) that was applied bo th perpendicular and parallel to the face of the cable (the face-on, FO, an d edge-on, EO, directions, respectively). For the cored cable the FO-measur ed effective ICR (FO-ICR), was 5.27 mu Omega. Those for the uncored cables were less than 0.08 mu Omega. AS shown previously for NbTi- and Nb3Sn-based Rutherford cables, the FO-ICR can be significantly increased by the insert ion of a core, although in this case it is still below the range recommende d for accelerator-magnet use. Postmeasurement dissection of one of the cabl es showed that the impregnating resin had permeated between the strands and coated the core with a thin, insulating layer excepting for some sintered points of contact. In the uncored cables the: strands were coated with resi n except for the points of interstrand contact. It is suggested that in the latter case this tendency for partial coating leads to a processing-sensit ive FO-ICR.