Coupling loss and contact resistance in cored stabrite cables - Influencesof compaction and variation of core width

AC loss due to coupling currents in a Rutherford cable can be modified by c hanging the interstrand contact resistance (ICS) by: adjusting the level of native oxidation of the strand, coating it, or by inserting a ribbon-like core into the cable itself. With regard to cored cables further effective-I CR adjustments can be achieved by changing: (i) the degree of compaction du ring manufacture, (ii) the thickness of the core at fixed overall thickness , and (iii) the width of the core. We report on Be results of magnetic and calorimetric AC loss measurements on stainless-steel-core stabrite cables w hich had been: (i) externally compacted by rolling to thicknesses of 0, 6, 9, and 11% below the standard thickness, (ii) internally compacted by being furnished with cores of thickness 1 mil (30 mum) and 2 mil(50 mum), and (i ii) furnished with cores whose widths, w(core) were about 20%, 50%, 75% and 100% of the maximum possible width. The measurements H:ere made in applied AC: fields that were directed perpendicular (face-on, FO) and parallel (ed ge-on, EO), respectively to the broad cables faces. It was noted that: (i) the introduction of the core dramatically reduced the FO loss, (ii) core in duced compaction decreased the side-by-side ICR and hence increased the EO loss, (iii) increases in either external or internal compaction still furth er increased the losses, particularly those in the FO direction (which of c ourse had already been strongly core-suppressed). The loss results were als o interpreted in terms of the FO-measured effective ICRs, R-perpendicular t o,eff, which were found to decrease from 350 mu Omega to 40 mu Omega during the compaction of a 170 degreesC-heat treated ("ctured", HT) cable and fro m II mu Omega to 10 mu Omega in the case of a 200 degreesC HT one. With inc rease in the w(core) of a 170 degreesC HT cable R-perpendicular to,eff incr eased from 1.8 mu Omega to 75 mu Omega, passing through 15 mu Omega at a w( core) of 66% w(core,max). The results show that there is an opportunity for achieving the LHC-target R-perpendicular to,(eff) of 15 +/- 15 mu Omega ei ther by compacting the standard cored cable (Tf= 200 degreesC) by 6 similar to9% or by reducing the width of the core (Tf= 170 degreesC) to within 66 +/-7% of w(max). We prefer the latter route since it exposes more of the st rands (some 34 +/-7% of them) to crossover-type current sharing.