Interstrand Contact Resistance in Nb3Sn Cables Under LARP-Type Preparation Conditions

The Nb₃Sn cables being developed under the LARP program will need to have suitable, reproducible, and uniform interstrand contact resistances (ICR) in the interests of accelerator- field quality (low coupling magnetization) and stability (current- sharing between strands). In the first of a pair of studies ICR was measured in response to variation of strand surface condition. As a sequel to this the present set of measurements explores the influence of cable preparation conditions on ICR, determined as before using calorimetric and magnetic AC-loss measurement techniques in face-on and edge-on applied AC fields. Uncored Rutherford cables were wound at Fermilab from OST MJR-type strand and wrapped with S-glass tape impregnated in most cases with a ceramic binder (applied before reaction HT). The HT/pressuriza- tion sequence of the cables was made to mimic as closely as possible the expected LARP magnet-fabrication schedules. Derived from maxima in the loss-vs-frequency curves was an ICR "inho- mogeneity-two ICRs for each cable pack each associated with a particular fraction of the strands. Furthermore, both of the ICRs, at 0.4 and 4 muOmega, would in a magnet be too small to satisfy the generally accepted magnetization requirements.