Effect of the film thickness on electron stimulated desorption yield from Ti-Zr-V coating

Abstract

With the benefits of evenly distributed pumping, low thermal outgassing rate and low photon-/electron-/ion stimulated desorption yields, non-evaporable getter (NEG) coating has been widely used in particle accelerators for many years. Our earlier work has demonstrated the different thickness of Ti-Zr-V coating in the range of 0.1–1 μm affects its pumping properties. In this study, the electron stimulated desorption (ESD) yields were studied for Ti-Zr-V coating deposited from a twisted target with its thickness less than 0.5 μm, while an uncoated sample was also measured as a reference. The ESD yields for H2, CH4, CO and CO2 were measured as a function of electron accumulated dose up to ∼2 × 1024 e-/m2 followed bakeout/activation by heating to 80, 120, 140, 180 and 250°C. After each ESD experiment the samples were full saturated with a mix of H2, CO and CO2. Both NEG coated samples demonstrate lower values in comparison to the uncoated one after heating/activation to temperatures up to 180°C for H2, up to 250°C for CH4, up to 140°C for CO and 120°C for CO2. The activation to 140°C is the most efficient way to reach lower pressure and avoid quick aging of the NEG coating. The thinner NEG coating provides a significantly lower ESD yield in comparison to the thicker one only after activation to 180°C, while their ESD yields are almost identical for each gas at the lower temperature.