How the sorbent microgeometry effects the sorptional characteristics of cryopumps

To calculate and construct cryopumps used in large high-energy physics inst allations, in ITER particularly, it is necessary to know the value of pumpi ng speed. Real surface of the sorbent is not flat. So a molecule of the pum ped gas can be reflected from this surface several times. The real surface of different sorbents is analysed by a scanning tunnel microscope: activate d coals Chemviron GFF/30, Chemviron SC II and non-evaporable getters. The r eal sticking coefficient value on the sorbent surface is calculated on the basis of integral trapping coefficient (pumping speed) of familiar experime ntal devices and of real geometric surface of the sorbent using the test pa rticle Monte-Carlo method. Obtained results for various types of sorbents m ay be useful for engineers-constructors of cryosorption pumps. (C) 1999 Els evier Science Ltd. All rights reserved.