Vacuum chamber conditioning and saturation simulation tool (VacuumCOST): Enabling time-dependent simulations of pressure and NEG sticking in UHV chambers

Modern particle accelerators, synchrotrons, and other machines requiring UHV frequently make use of NEG coatings to achieve low pressures and resulting high beam stability and lifetime. It is the nature of NEG pumps and coatings, that a limited amount of gas can be pumped before saturation is reached, at which point the NEG must be re-activated to pump efficiently again. While the pumping mechanism and absorption limits are well understood and software packages exist for simulating the steady-state vacuum systems, there is a need for simulating the temporal evolution of the pumping capability of NEG coatings in regions of high outgassing rates such as near crotch absorbers. This paper presents a simple framework, written in Python, for running time-dependent simulations of NEG-coated vacuum systems in molecular flow, by making use of the command-line interface of the already widely used MolFlow simulation software. It also compares simulation results with accelerator pressure measurements.