Origin of possible contamination introduced by a turbomolecular pumping system

Abstract

Turbomolecular pumping groups are widely used in accelerators for the pre-evacuation and during the bake-out of the vacuum system. A major requirement for these groups, apart from pumping speed considerations, is the cleanliness of the vacuum produced. In an attempt to clarify this question, a bakeable low-pressure vacuum system has been constructed to allow the direct comparison of the contamination introduced by a turbomolecular pump and by an ideally clean cryopump. This contamination has been checked by the quantitative analysis of the residual gas as well as of the gases desorbed from surfaces under electron bombardment. Contamination by the rotary pump oil is only apparent below 40% of the turbomolecular pump nominal rotation speed. When the pump is stopped, the system is contaminated by heavy hydrocarbons which can be eliminated by a 300°C vacuum bake out. Abstract Turbomolecular pumping groups are widely used in accelerators for the pre-evacuation and during the bake-out of the vacuum system. A major requirement for these groups, apart from pumping speed considerations, is the cleanliness of the vacuum produced. In an attempt to clarify this question, a bakeable low-pressure vacuum system has been constructed to allow the direct comparison of the contamination introduced by a turbomolecular pump and by an ideally clean cryopump. This contamination has been checked by the quantitative analysis of the residual gas as well as of the gases desorbed from surfaces under electron bombardment. Contamination by the rotary pump oil is only apparent below 40% of the turbomolecular pump nominal rotation speed. When the pump is stopped, the system is contaminated by heavy hydrocarbons which can be eliminated by a 300°C vacuum bake out.

Use of monoatomic and polyatomic projectiles for the characterisation of polylactic acid by static secondary ion mass spectrometry

“…Above m/z 300, no significant signals are detected. The ions up to m/z 40 can originate from hydrocarbon contamination from air or even vacuum,51–54 and have therefore low specificity for PLA.…”

Optical properties of magnetron-sputtered and rolled aluminum

“…22 Oxide within the bulk of MS aluminum originates from the reaction of water and/or oxygen remaining in the vacuum chamber with aluminum as it is deposited and as it is in flight between the target and the substrate. Both oxygen and water are present in the residual gas of a nonbaked turbomolecular pumped system.…”