Nb Coatings for Bellows used in SRF Accelerators

High-current particle accelerators have need for low-impedance bellows connecting accelerating cells and in other areas of the accelerator. Typical techniques to decrease surface impedance are to use shields of superconducting Nb, however, as these shields move they produce particulates that can be detrimental to operation if they find their way into the storage ring. Alameda Applied Sciences Corporation has demonstrated high-quality Nb coatings on flexible metal bellows. This superconducting layer leads to a decrease in the surface resistance at cryogenic temperatures and a decrease in the power consumption of the bellows. AASC will further engineer this superconducting layer by improving the film adhesion to the bellows and further investigating the RF properties of a superconducting bellows. In Phase I, two stainless steel bellows were coated with Nb and RF measurements were performed to determine the Q of the resonant structure from 300 K to 5 K. Additionally, initial tests to determine the adhesion of cathodic arc films to stainless steel were carried out. In Phase II, further adhesion tests will be performed and process variables will be optimized with film adhesion in mind. Cryogenic RF tests will be carried out to further understand the behavior of a superconducting thin film bellows in a simulated environment. Commercial Applications and Other Benefits: The production of a particulate-free, low-impedance bellows has application in many of todays high-current particle accelerators, such as accelerator light sources and spallation neutron sources.