High Temperature, Superconducting, Thinfilm Coatings for RF Accelerator Cavities

78840S05 Superconducting radio frequency (RF) accelerator cavities are traditionally constructed from pure Niobium metal. However, niobium is expensive and difficult to manufacture, leading to increased material and fabrication costs. Compounding the cost problem is the fact that the majority of the superconductor is wasted because the majority of the material is used to meet the mechanical strength requirements of the system, not to conduct current [i.e., the London penetration depth of the superconducting current is very thin (~60 nm), whereas the wall of the cavity must be thicker (~3 to 4 mm)]. In this project, a Coaxial Energetic Deposition (CED) process will be used to coat the inside of copper RF elliptical accelerator cavities with superconducting MgB2 films with comparable or superior accelerating gradients and quality factors to Niobium cavities, but with further reduced fabrication and operation costs due to the higher critical temperature of MgB2. Phase I will test the feasibility of using the CED process to deposit superconducting MgB2 films on the inside of elliptical RF cavities by: (1) using the CED process to coat four 5 cm inside diameter copper tubes, about 25 cm in length and several sapphire and copper witness plates with MgB2 films; (2) measuring the superconducting transition temperature and Residual Resistivity Ratio for the CED films to determine superconducting properties; (3) performing SEM and x-ray diffraction analysis to assess general film properties; and (4) coating one or more actual RF elliptical copper cavities with MgB2. Commercial Applications and Other Benefits as described by the awardee: The superconducting thin film coatings for accelerator cavities should reduce the development and operating costs of particle accelerators. Thus the installation and operating costs of experimental particle physics projects will decrease while the ability to probe fundamental physics questions with higher energies will increase. In addition, the capabilities of the CED process will be further developed, which could lead to such applications as protective coatings for coal gasification, olefin manufacturing, and gun barrels for the military.