The sources of electron-induced contamination in kinetic vacuum systems

The relative importance as contaminants of various materials which are used in the construction of kinetic vacuum systems was assessed by introducing them into a clean system and measuring the carbonaceous deposit formed on a surface bombarded by electrons. In order of descending contaminating power are diffusion pump oil (hydrocarbon), vacuum grease, various types of rubber gasket material, silicone pump oil, and vacuum wax. Uncleaned metal surfaces are also a considerable source of contamination, and methods of cleaning are discussed. Experiments carried out on the dependence of contamination rate upon the temperature of the bombarded surface showed that a 10 times reduction could be expected from raising the temperature to 200°C. A cold trap at - 15° C, surrounding it, was found to be equally effective.