Optimization of the BCP processing of elliptical nb srf cavities

At present, the electropolishing (EP) process is considered the key technology unleashing the capability to produce Niobium SRF cavities performing at or above 35 MV/m. Nevertheless buffered chemical polishing (BCP) remains a cheap, simple and effective processing technique for single grain high gradient and polycrystalline lower gradient cavities. BCP will be adopted to chemically process the third harmonic 3.9 GHz cavities being fabricated at Fermilab [1]. The dimensions and the shape of these cavities yield a strong nonuniformity in the material removal between iris and equator of the cells. This paper describes the thermal-fluid finite element model adopted to simulate the process, the experimental flow visualization tests performed to verify the simulation and a novel device fabricated to solve the problem