Combination of a getter pump with turbomolecular pumps in UHV applications

This work reports on RGA studies relative to pump-down and ultimate pressur e experiments made on a 401 UHV chamber with a specially designed non-evapo rable getter (NEG) pump operated in series with the main pumping group, com prising a 600 l/s hybrid turbo pump backed by a 12 m(3)/h rotary pump. Expe riments were also made with a 50 l/s turbomolecular drag pump inserted betw een 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 usi ng five NEG elements arranged around the walls of a cylindrical cartridge i nserted inside a stainless-steel nipple having an inner diameter of 150 mm. A single NEG element, consisting in a empty set 5 mm, 720 mm long rod, sha ped as a sinusoid, was prepared by sintering ca. 20 g of pure titanium on a empty set 0.5 mm nichrome wire. The NEC pump allowed for a tenfold reducti on of H2O partial pressure and a reduction of the ultimate pressure from 1 x 10(-9) to 1 x 10(-10) mbar. In particular, because of the sorption charac teristics for hydrogen of NEG pumps, the H-2 partial pressure could be sign ificantly reduced by effectively dealing with the hydrogen backstreaming, t ypical of turbo pumps. (C) 1999 Elsevier Science Ltd. All rights reserved.