Parametrization of the niobium thermal conductivity in the superconducting state

Thermal conductivity measurements of niobium sheets manufactured for deep-drawing of superconducting cavities have been gathered. Due to the differing histories of the niobium samples and a wide range of metal purities (35<RRR <1750), the data demonstrate a large scatter of thermal conductivities. An attempt was made to obtain an analytical expression with realistic parameters for the thermal conductivity between 1.8 K and 9.25 K. The set of parameters deduced from a least square fit of experimental data is not very different from those yielded by the theory of superconducting metals, taken as a starting point. This should make it possible to obtain a reasonable estimate of the thermal conductivity of niobium in this temperature range, once the RRR and the past history of the metal samples had been determined. (author)