The effect of cladding material on ac losses of commercial Nb3Sn tapes

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Abstract
Ac losses of commercial Nb3Sn tapes have been measured before and after removal of the normal metal cladding which is used to stabilize the superconductor. It is shown that materials which are frequently used to assist in bonding the normal metal to the Nb3Sn surface give rise to hysteretic losses which are much larger than those of the Nb3Sn itself in the low‐field region of interest for power transmission, below 1000 Oe. Examples of such materials are superconductive Pb–Sn solders used in cladding tin‐diffused tapes and ferromagnetic nickel flashes used in silver plating vapor‐deposited tapes. These lossy materials are not essential and can be eliminated in tapes which are properly designed for power transmission. It is also shown that eddy current losses are acceptably small for normal metal cladding thickness of the order of 25 μm (ρ∼10−8 Ω cm).