LABORATORI NAZIONALI DI LEGNARO
In the present talk, based on experimental evidence, we consider the hypothesis that the Q‐slope is related to enhanced thermal boundary resistance at the Nb/Cu interface, due to poor thermal contact between film and substrate. We have developed a simple model that directly connects the Q versus E acc curves to the distribution function f(RNb/Cu)of RNb/Cu values at the Nb/Cu interface over the cavity surface. Starting from different Q versus Eacc experimental curves from different sources, using typical ‘inverse problem’ methods, we deduce the corresponding distribution functions generating those curves.
The results show, for all the examined cases, very similar functional dependences of the defect distributions and prove that, to describe the experimental Q versus Eacc curves, it is sufficient to assume that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate.