Thermal behaviour of superconducting niobium cavities is investigated especially focusing on the Kapitza boundary resistance. First systematic measurements of the thermal boundary resistance are performed on samples with well characterised thermal conductivity (RRR values) and surface morphology (chemically etched or electropolished). The experimental data are used in a simple model, calculating the heat flux to the superfluid helium bath. These results show the relative importance of the Kapitza resistance with respect to the thermal conductivity. Also they indicate that best conditions are reached when using high RRR niobium with rough chemically etched outer surfaces.
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