Simple method to measure the thermal conductivity of technical superconductors, e.g., NbTi

A technique is described which allows the measurement of the thermal conductivity kappa of superconductors below T(c) without the use of a thermometer, if T(c) is known. The method is particularly adapted to technical superconductors of poor thermal conductivity. It is convenient to use as sample a superconducting wire or band provided with a high conductivity matrix of a normal metal, which has to be removed from the test length. The stabilized ends of the sample are thermally anchored to a heat sink of variable temperature T. A current I flowing through the conductor holds the middle part of the test length in the normal state due to Joule heating. The length of the normal section and hence the voltage appearing on the sample are a functions of I and FkappadT. The variation of the temperature of the heat sink then allows the determination of kappa (T). Results for two NbTi samples are included.