Modeling and Optimization of the Chemical Etching Process in Niobium Cavities
Niobium cavities are an important component of integrated NC/SC high-power
linacs. Researchers in several countries have tested various cavity shapes
and concluded that elliptically-shaped cells and buffered chemical polishing
produce the best performance. The objective of this paper is to study and
optomize the process on the effect of chemical etching on the surface roughness.
Chemical etching of the inner surface of the cavity is achieved by circulating
acid through it. The acid interacts with the surface and eliminates imperfections.
During etching, the end of the cavity is blocked. A pipe with baffles is inserted
within the cavity to direct the flow along the surfaces. A finite element
computational fluid dynamics model is developed for the etching process. The
problem is modeled as a two-dimensional, axisymmetric, steady state fluid
flow problem. This model is used to study the parameters affecting the uniformity
of the etching process, such as flow rate and geometry of the baffle. The
model is parameterized so it can be used within an optimization program to
improve quality of the surface finish.