Restgases
Restgases, or residual gases, are the gas species that remain in a vacuum system after pumping. They originate from outgassing of chamber walls and components, permeation through seals, leaks, desorption of adsorbed films, and, in some cases, pump oil decomposition or getter activity. The partial pressures of these gases set the background pressure and can influence experimental conditions.
In ultra-high vacuum, the composition is typically dominated by hydrogen, water vapor, carbon monoxide, carbon dioxide,
Residual gas analysis (RGA) is used to monitor restgases. A mass spectrometer detects desorbing gas species
Impact: Restgases contribute to surface contamination, chemical reactions, and unwanted sputtering in vacuum devices. In accelerators
Control and mitigation: Bake-out at elevated temperatures; selection of low-outgassing materials and clean assembly; use of