JR Macdonald Laboratory 2000 Summer Short Course: Introduction to Vacuum Physics and Technology: ---------------------------------------------- Problem #2: A differentially pumped gas target has 0.1" diameter beam entrance- and exit apertures. It is mounted in the center of a 4" 4-way cross (4x3.75" long). It is sealed with 4.5" x .1" Buna-N O-rings. The differential pumping is accomplished with a TPU400 turbomolecular pump (6" inlet port). The TPU400 is adapted to 4" with a zero-length reducer and connected with a 7.5" long, 4" diameter nipple to the 4 way cross. The TPU400 pump is backed by a DUO30A rotary vane pump. Question A: What is the expected hydrogen pressure in the differential pumping region if the gas target is kept at 0.1 Torr Hydrogen? Question B: What is the expected nitrogen pressure in the differential pumping region if the gas target is kept at 0.1 Torr Nitrogen? Question C: What is the expected nitrogen pressure in the differential pumping region if we eliminate the 7.5" long 4" diameter nipple?