Thermal Limitations in Superconducting RF Cavities: Improved Heat Transfer at Niobium-Helium Interface

摘要

The accelerating gradients in superconducting RF cavities can be limited by excessive temperature rise on the inner surface. In some circumstances, such as high RF frequency or anomalous losses, improved heat transfer at the niobium-helium interface can increase the achievable gradient. Different surface morphology techniques have been applied to reduce the limitation at the thermal interface. These techniques include varying surface roughness and forming cooling channels (embedded fins) in the surface. Heat transfer measurements on several niobium samples of different surface states, but same bulk purity at both Helium I and II (super-fluid) temperature regimes are planned. Initial measurements to validate the experimental setup on one sample are presented. Comparison of the test measurements is made with the existing literature data. The surface characterization uses a high-resolution 3D optical nano-scope. Finally, the influence of these interface surface techniques on the performance of the cavities will be discussed.