COUPLING-CURRENT AND PERSISTENT-CURRENT MAGNETIZATIONS IN Nb[sub 3]Sn RUTHERFORD CABLES AND STRANDS

Abstract

Calorimetric and magnetic measurements of AC loss in Nb 3 Sn Rutherford cables were accompanied by magnetic measurements of persistent-current (hysteretic) loss in strands extracted from those cables. From the cable-loss measurements it is shown that the introduction of a stainless steel core increases the effective interstrand contact resistance (ICR), initially 0.3 µΩ, by more than two orders of magnitude. Uniaxial pressure applied to the cable during winding and subsequently, seemingly by reducing side-by-side contact, increased the ICR. In an edge-on applied AC field the persistent-current cable loss was fully accounted for in terms of the individual-strand loss. The persistent-current loss measured for the cable in a face-on applied field was higher that that in an edge-on applied field, this may have been due to demagnetization effects.

Coupling Loss, Interstrand Contact Resistance, and Magnetization of Nb$_{3}$Sn Rutherford Cables With Cores of MgO Tape and S-Glass Ribbon

“…These bracket the average VSM-measured extractedstrand loss, viz: 3.55 0.09 10 J/m (reduced from the measured 4.44 0.11 10 J/m by a factor 0.8 to take into account the packing factor of the parent cable). Thus the strand falls roughly midway between the FO and EO cable values, which can be compared to previous results [9]. Qualitatively confirmed by separate experiment and calculation this effect is attributed to the demagnetizations associated with a flat superconductor (e.g.…”

“…The of cable NC, at 0.33 , agrees well with all previous results on uncored Nb Sn cables whose s have been found to be in the range of 0.1-0. 4 [1]- [9]: well below the optimal 15 5 [12]. Inclusion of the plain MgO and s-glass cores raised to about 9 , a value that dropped to 6.8 after the ceramic binder was introduced.…”

“…These are unacceptably low values, to correct for which Nb Sn Rutherford cables have been provided with metallic (albeit "insulating") cores of various types and widths. As described in [1]- [9] stainless steel (SS) ribbons or Cu-SS laminates have been used with varying degrees of success. Then in seeking a more flexible core, and one that is more compatible with the cabling process, the Lawrence Berkeley National Laboratory (LBNL) suggested the use of MgO-paper tape and woven s-glass ribbon, respectively.…”

“…So a compromise between ICC and BICC reduction and magnet stability is sought leading to the recommendations that should be very small, although not less than 0.2 [11], and that should be about 15 5 [12]. But the wind-and-react assembly of Nb Sn Rutherford cables in an accelerator magnet typically leads to s in the vicinity of 0.1-0.4 [1]- [9]. These are unacceptably low values, to correct for which Nb Sn Rutherford cables have been provided with metallic (albeit "insulating") cores of various types and widths.…”

“…C OUPLING loss and interstrand contact resistance has been the subject of a long series of studies of Rutherford cables wound with bare-and coated NbTi, Nb Al, and Bi:2212 (for references see [1]), and subsequently Nb Sn [1]- [9]. The suppression of interstrand coupling currents (ICCs) and "supercurrents" [10] (i.e.…”