Speaker
Description
"The Future Circular Collider (FCC), foreseen to be built at CERN, relies on the Nb/Cu technology for the 400 MHz RF system. In view of reaching the requested specifications, it is of uttermost importance to push the SRF performance of the Nb thin films to its limits. To do so, it appears critical to understand what are the underlying physical phenomena that drive the Q-slope. Such an effect has been tracked back to be partly due to magnetic flux pinning in the films that eventually dissipates power once the applied RF field amplitude increases [1].
Nb thin films elaborated using DC-biased HiPIMS are known to lead to dense films and address the contribution to the Q-slope attributed to film porosities [2,3]. Using the critical current density, JC, as a metric of the density of pinning sites in our films, we find a dependency with film thickness as well as with the ion bombardment energy. We manage to identify the defect family responsible for tuning the Jc and use an analytical model to explain the optimal bombardment energy found to minimize it. This study leads to the identification of an optimal bias voltage value to be used in view of minimizing defects in Nb films. "
