Mitigating the detrimental effect of hydrogen impurities on secondary electron yield of amorphous carbon thin films: A study on power density, and discharge modes

Amorphous carbon thin films with low Secondary Electron Yield (SEY) are critical for applications where electron multipacting limits achievable performance. Such films are effective to mitigate electron cloud formation within the vacuum beam lines of particle accelerators such as the Large Hadron Collider and the Super Proton Synchrotron at CERN. They are now also being implemented in the new Electron Ion Collider under construction at Brookhaven National Laboratory. Research over the last decade has highlighted the significant role of hydrogen presence in the plasma discharge during deposition. Hydrogen incorporation in the films has been shown to increase the SEY, posing a key challenge in coating the extensive beam pipes for particle accelerators. In this study, the effects of power density and discharge mode, i.e. Direct Current (DC) and High-Power Impulse Magnetron Sputtering (HiPIMS), on the SEY of amorphous carbon films are examined. These films were produced by sputtering in an argon atmosphere with 1.3 % D₂ to simulate hydrogen-like impurities typically arising from outgassing in the beam pipes and the deposition system. The D₂ consumption during the coating process was monitored by mass spectrometry and is correlated with the SEY. The findings indicate that higher deposition powers result in films with lower SEY, suggesting a reduced deuterium incorporation. Additionally, for the same average power density, films deposited in HiPIMS mode exhibit a lower SEY compared to those deposited in DC mode. The results are discussed in the context of hydrogen incorporation mechanisms in carbon films, with a view towards optimizing coating system design and process parameters. • Graphitic carbon thin films can reduce Secondary Electron Yield (SEY) of surfaces. • Discharge power impacts the mitigation of D 2 impurities in the Ar process gas. • Sp 2 fraction in carbon films correlates with deuterium consumption and SEY. • Higher discharge powers favour sp 2 in films sputtered in Ar-D 2 and reduce SEY. • Use of High-Power Impulse Magnetron Sputtering can minimize deuterium consumption.