Abstract
A compact cryogenerator called “Cryopet” has been applied as a refrigerator for the cold trap and baffle of the 4-inch diffusion pump. This “Cryopet” works by the principle similar to the MacMahon-Gifford cycle, and generates about 45w of the cold at -150°C. The cold trap filled with ethyleneglycol or methanol as heat transfer medium was cooled down, and ultimate temperature of -130°C was obtained. The conventional chevron baffle was also cooled by this machine, and temperature got down to -80°C. In this two methods, the ultimate pressures of the systems were almost comparable to the case when the trap was cooled by liquid nitrogen.
The oil backstreaming rates from the diffusion pump were also measured. The oil sticked at the bottom of the trap was dissolved in benzene and the solvent was evaporated, then remained oil was weighed by a precision chemical balance. In comparision with the backstreaming rate without both the baffle and top-jet-cap, we found the rate was decreased to about 10-3 when the baffle was cooled by water, and to less than 7 × 10-4 when “Cryopet” or liquid nitrogen was applied to the baffle.
