拡散ポンプ排気系の回転ポンプ油による汚染とその防止

概要

論文の詳細を見る
The mechanism of the oil contamination in a DC-705 oil diffusion-pumped uhv system has been investigated using a high sensitive residual gas analyzer. The system was equipped with a rotary pump and a 4-in. diffusion pump with a water-cooled baffle. It was found that main contaminants in the system come from the cracking of the rotary pump fluid in the diffusion pump boiler. The degradation of the ultimate pressure is proportional to the product of the concentration of the rotary pump fluid and the cracking rate in the hot boiler. In order to prevent the inflow of the fluid into the boiler, it is effective to make a temperature gradient along the foreline tube of the diffusion pump and to evaporate the high vapor pressure fluid on the wall surface warmed up to 70-100°C. For the system being out of operation, we have proposed to place a bakable valve on the foreline which is closed except when both the foreline tube and the valve are warming up with the diffusion pump operation.