Test Particle Monte-Carlo modelling of installations for NEG film pumping properties evaluation

Two installations were built in the ASTeC vacuum science laboratory to investigate the pumping properties of non-evaporable getter (NEG) films. An important parameter to characterise the pumping properties is the film sticking probability (α). Test Particle Monte-Carlo (TPMC) models were used for accurate evaluation of NEG film sticking probability from pressure readings during gas injection. The results of these models were used for interpreting the results of measurements in different experimental configurations: planar, cup and tubular samples. It was shown that there is a difference between simple formulas used in vacuum technique and TPMC results which is significant for α > 0.1 with planar samples, for α > 0.01 with cup samples, and in the full range of α for tubular samples. It was also shown that the gauge positions are very important, the exact position of the gauge or RGA ionisation chamber should be used in the modelling.