Residual gases in oil and mercury pumped systems: J H Singleton,J Vac Sci Technol, 3 (6), Nov–Dec 1966, 354–355

Abstract

This work reports on RGA studies relative to pump-down and ultimate pressure experiments made on a 40 l UHV chamber with a specially designed non-evaporable getter (NEG) pump operated in series with the main pumping group, comprising a 600 l/s hybrid turbo pump backed by a 12 m3/h rotary pump. Experiments were also made with a 50 l/s turbomolecular drag pump inserted between the exhaust of the hybrid turbo pump and the intake pipe of the rotary pump. The NEG pump, located on top of the main turbo pump, was realized using five NEG elements arranged around the walls of a cylindrical cartridge inserted inside a stainless-steel nipple having an inner diameter of 150 mm. A single NEG element, consisting in a ∅ 5 mm, 720 mm long rod, shaped as a sinusoid, was prepared by sintering ca. 20 g of pure titanium on a ∅ 0.5 mm nichrome wire. The NEG pump allowed for a tenfold reduction of H2O partial pressure and a reduction of the ultimate pressure from 1×10-9 to 1×10-10 mbar. In particular, because of the sorption characteristics for hydrogen of NEG pumps, the H2 partial pressure could be significantly reduced by effectively dealing with the hydrogen backstreaming, typical of turbo pumps.