Magnetic Measurements of Interstrand Contact Resistance in<tex>$rm Nb_3rm Sn$</tex>Cables in Response to Variation of Pre-Heat-Treatment Condition

Abstract

Inductive (pickup-coil) magnetometry was used to measure AC loss in uncored Nb 3 Sn Rutherford cables in the perpendicular and parallel orientations of the applied field. The four cables selected for study had widths of 8, and 13 mm and strand counts of 20 and 30, respectively. Under various surface conditions they were reaction heat treated (RHT) then vacuum impregnated with resin in preparation for measurement. The magnetic measurements were made at 4.2 K in sinusoidal fields of amplitude 400 mT and frequencies of 5 to 90 mHz, The total per-cycle loss so obtained was used to deduce the "crossover" interstrand contact resistance (ICR). Attention is focused on the ICRs of one particular 8-mm/20-strand cable measured in this and previous studies under several pre-RHT conditions: (i) as-received, (ii) acetone-degreased, and (iii) acetone-degreased then HCl-deoxidized then acetone rinsed. A comparison is also made to the ICR of a sub-size cored Nb 3 Sn cable.

Magnetic measurement of interstrand contact resistance and persistent-current magnetization of Nb3Sn Rutherford cables with cores of MgO tape and woven S-glass ribbon

“…For the present cables the uncored <R eff > AV. of 0.2 µΩ agrees well with previously measured results for uncored Nb 3 Sn cables [7][8] [9] but would lead to an unacceptable M coup,LARP,0.2µΩ = 338 kA/m. The presence of the insulating cores with <R eff>AV.…”

“…For the NbTi-wound LHC-inner cable (with <w/t> = 7.94, L p = 55 mm, N = 28, R c = 20 µΩ) ramping at 6.5 mT/s Equation (1) provides our "bench-mark" coupling magnetization of M coup = 1.85 kA/m. The same cable wound with Nb 3 Sn strand, under the pressurized windand-react conditions that it would experience in a magnet, with R c s such as 0.15 µΩ, 0.16 µΩ [7], 0.24 µΩ [8], 0.3-0.36 µΩ [7] and 0.4 µΩ [9], would exhibit coupling magnetizations some two orders of magnitude larger than this. Thus as frequently pointed out a core is needed to increase the R c of Nb 3 Sn Rutherford cables.…”

Strand level modeling of contact resistance and coupling loss for EU-DEMO-TF prototype conductors

“…Although still speculative, the need for using R ip may be due to the cable geometry and associated manufacturing process, with different compaction load for both directions. This could be typical for rectangular cable with a large aspect ratio, as commonly observed in accelerator type of cables [26], different from the round ITER conductors with more homogeneous cable compaction in all directions. The fact that the same values have been found for R ip and R ss , with JackPot to match the AC loss in parallel and perpendicular field configurations, supports this hypothesis.…”

Effects of Core Type, Placement, and Width on the Estimated Interstrand Coupling Properties of QXF-Type Nb₃Sn Rutherford Cables

“…Over the years, the calorimetrically and magnetically measured Reff (i.e. Rc) values we have obtained for uncored Nb3Sn cables have been: 0.24 [9], <0.1 [17], 0.17, 0.37, 0.39 [18], 0.24 [19], 0.37 [20], 0.23 [21], 0.15, 0.36 [22], 0.4 [23], 0.37 [24], 0.22 [25], 0.10, 0.17. 0.25 [26], 0.33 [27] for an average of 0.26 ± 0.1 μΩ along with two "high" values of 1.76 [22] and 1.93 [18].…”