Coupling current control in stabrite-coated NbTi Rutherford cables by varying the width of a stainless steel core

AC loss measurements were made on a series of Rutherford cables wound from stabrite-coated NbTi/Cu multifilamentary strand, from the results of which interstrand contact resistances were calculated. The 28-strand, 15 mm wide, LHC-inner type cables contained stainless steel cores of widths varying from 0 (no core) to 12.7 mm. Measurements were made on 4-layer cable packs. Two main preparation (curing) cycles were used: (1) heat treatment (HT) at 170°C under 80 MPa followed by pressure release and re-application before measurement; (2) HT to 200°C and maintenance of the pressure until after measurement. One additional protocol-(1)-treated pack was prepared from cables that had received a diffusion HT of 200°C/8h in air following a CERN-recommended prescription for achieving a satisfactory contact resistance (ICR). Calorimetric loss measurements were made on all samples using a sinusoidal field with an amplitude of 400 mT. It is concluded that by adjusting the width of a stainless steel core the effective ICR, R⊥ ,eff , of a stabrite-coated LHC-inner-type Rutherford cable can be varied over a wide range, and in particular that a published target of 15 μΩ could be attained with a core width of 8.5 mm - a little more than one-half the width of the cable, leaving the rest of the cable free for current sharing. It is also concluded that in terms of R⊥ ,eff the OSU-administered CERN diffusion HT was equivalent to inserting a 9.5-mm-wide core.