An evaporating system using a liquid helium cryopump was constructed and its pumpdown curves and pressure change during evaporation were measured. Using this system, the internal stress and the electrical resistivity of deposited aluminum films were investigated. They are compared with the properties about the film deposited in the diffusion pump system and the difference between them is discussed.
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.