Interstrand contact resistance and AC loss of a 48-strands Nb3Sn CIC conductor with a Cr/Cr-oxide coating

摘要

The interstrand contact resistance (Rc) between crossing strands in Cable-In-Conduit Conductors (CICC's) determines the coupling loss and the stability against local disturbances. The surface oxidation, surface roughness and micro-scale sliding of the contact surfaces are key parameters in the Rc. The level of surface oxidation is influenced by manufacturing parameters in the strand and cable production, the plating procedure determining the crystalline structure and by the heat treatment. A new process of making a more stable oxide has been developed and characterised. The Cr coating is actually build up out of two different layers. The first layer is a hard Cr coating, identical to the standard Cr layer previously used. On top of this a layer of blade Cr oxide is deposited electrolytically. The coupling loss time constant and Rc are measured on a 48-strands CIC Conductor with this double-coated strand material. The void fraction amounts to 36% and the strand, cabling and jacketing are identical to those used in the previous chrome vendor comparison action. The results, presented in terms of Rc, time constant n¿, and the atomic concentration of oxygen (acO) in the peripheral region of the strand, are compared to previous results from single coated strands