Funded Projects 2018

Influence of Nitration of SRF grade Niobium on Kapitza Resistance and Thermal Conductivity

Copyright: Dr. Marc Wenskat

Dr. Marc Wenskat (UHH)

Project Partners: Guilherme Dalla Lana Semione, Christopher Bate

Superconducting radio-frequency (SRF) cavities are the workhorse for modern accelerators, whether for the European Spallation Source, the European XFEL or LCLSII and the cavity production for the European XFEL set standards. But in recent years, new treatments have emerged. In particular the LCLSII cavity production is based on a treatment which mechanisms remain mysterious. These so called “nitrogen doped” cavities have a lower surface resistance RS by a factor 2-3 in the operational range for a continuous wave machine, which drastically reduces operational costs, but the maximum accelerating field was also reduced by about 30%. Another improvement is the “nitrogen infusion” process, which reduces Rs but maintains the accelerating field. This process is difficult to control and not all relevant process parameters are yet identified. None of the new treatments are understood in terms of surface processes or relation to cavity performance. We want to investigate our new hypotheses to explain the reduced accelerating field for nitrogen-doped cavities. In parallel we will test a theory for the origin of the reduced Rs. If the hypothesis is found to be correct, the limitation of doped cavities can be overcome. But even more important, a new insight in the relation of surface properties and cavity performance would be achieved.