Molecular conductance of a contact-free labyrinth seal used for the contamination control of a cryogenic space instrument

This study presents the molecular conductance measurement of a labyrinth seal introduced for the Contamination Control Cover which is protecting the cryogenic optical surfaces of the mid-infrared instrument of the James Webb Space Telescope against molecular contaminants from the environment. The conductance has been measured in the molecular pressure regime between 10−7 and 10−3 mbar within a temperature range of 300 K and 10 K for several typical components of the expected residual gas such as H2O, NH3, CO2, H2, NO, alcohols and hydrocarbons as well as standard gases such as N2 and He. The measurements have been repeated with a thin orifice to verify the systematics. The results are well consistent with numerically derived values and demonstrate a robust understanding of the design and performance of the labyrinth seal.