Study of Bi(2223) tapes with low thermal conductivity

In this paper we describe an apparatus for static measurements of the thermal conductivity of Bi(2223)/Ag-sheathed tapes in a temperature range going from 4 K to 200 K. The standard experimental technique has been improved by the implementation of an original sample arrangement that minimizes the thermal losses by radiation. We have performed a set of measurements of thermal conductance on Bi(2223) tapes with different metallic sheaths. The thermal conductance varies within four order of magnitude when the sheath is changed from pure Ag to Ag alloys. The thermal conductivity of several AgAu and AuMg alloys has been extracted from these measurements, discussing then the origins and the mechanisms for the observed unpredicted material properties.