Outgassing and Desorption of the Stainless Steel Beam Tubes after Different Degassing Treatments

摘要

Chemical cleaning, vacuum firing, glow discharge cleaning and insitu bakeout have become standard practice for lowering the outgassing rate and removing surface contaminants in the ultra high vacuum systems of particle accelerators and storage rings. This paper presents the work done with the thermal outgassing of several long stainless steel (304LN and 316L) beam chambers with areas of more than 1 x 10 sup 4 cm sup 2 . They were measured between 20/degree/ C and 500/degree/ C after vacuum firing, glow discharge cleaning or reactive gas (nitric oxide) cleaning. Outgassing rates of low 10 sup -13 and low 10 sup -14 Torr .1/s.cm sup 2 were achieved for H sub 2 and CO, respectively, with vacuum firing alone. The outgassing of H sub 2 in this temperature range is consistent with that due to bulk diffusion with an enthalpy of 9 +- 1 Kcal/mole. The photon stimulated desorption of the chamber surface after the above treatments were also studied by exposure to an intense photon beam at the National Synchrotron Light Source. The effectiveness and merits of reactive gas cleaning in removing the surface contaminants in large vacuum systems are compared to those of vacuum firing and glow discharge cleaning. 14 refs., 5 figs. (ERA citation 14:001518)