Copper Cold Spray for Mechanical and Thermal Stabilization of SRF accelerator Components

Superconducting linear accelerators are in a growing demand in research and industrial applications. Currently, these devices are exclusively made from niobium, and advances in the art have been driven largely by new recipes to process the niobium surface, making the accelerators more efficient and costs effective. Unfortunately, these improvements come at the expense of other material properties, such as mechanical strength and thermal conductivity. The ability to make multi-material accelerators, while preserving the superior superconducting properties of niobium, is a topic of significant interests. Cold spray is a relatively new metallurgical coating process which can potentially solve this material optimization problem. Cold spray involves accelerating metal powder in a stream of gas to very high speeds and then impacting a solid substrate. The impact is so severe that the oxide layers normally separating the metals is pushed out, resulting in a strong metal-to-metal bond. Cold spray is unique in that the powder is deposited without melting, which should minimize the risk of contaminating the niobium surface. This project will conduct the first-known study of cold-sprayed copper coatings onto niobium for superconducting RF accelerator components. The objective is to assess the compatibility of cold- spray copper with accepted SRF processing recipes and operating conditions. Some known risk factors, such as coating delamination, will be investigated experimentally in order to determine the feasibility of the cold spray approach towards SRF components fabrication. Multi-material SRF accelerating structures could significantly reduce the infrastructure required to operate these devices and reduce cost of ownership for the research and industrial accelerator systems. This would simplify the technology and expedite its adaptation by industrial applications.