ON THE EFFECT OF BAKEOUT FOR THE PUMPING SPEED DEPENDENCE OF OUTGASSING RATE IN A STAINLESS-STEEL CHAMBER

In order to investigate the effect of bakeout on the dependence of out gassing rate on pumping speed in a vacuum system, the outgassing rates of a test chamber at room temperature without baking and after bakeou t at 100 and 250 degrees C were measured as a function of pumping spee d. The measuresd outgassing rate q(Torr . l/s . cm(2)) obeys power law q = C(SIA)(m) where C and m (0 < m < 1) are constants, S/A is the pum ping parameter defined as the ratio of the pumping speed S(l)/s) and t he surface area A(cm(2)) of the chamber, and the variable range of S/A is from 2.46 x 10(-5) to 1.26 x 10(-2) (l/s . cm(2). The obtained pow er laws at RT and 100 degrees C have two different exponents but that at 250 degrees has only one exponent. The experiment shows that the ba keout weakens the pumping speed dependence on outgassing rate. In addi tion the theoretical consideration for the effect suggests that the st icking probability of the wall plays an important role on the pumping speed dependence. Copyright (C) 1996 Elsevier Science Ltd.