Experimental study on scaling law of outgassing rate with a pumping parameter

The outgassing rate of a small test chamber made of 304 type stainless steel has been measured as a function of pumping speed in a range from 0.3 to 200 ιs. In the experiment the chamber has been first exposed to the air and then pumped with different pumping speeds for 3 days at room temperature of 20 degC without baking. The typical outgassing rates of the chamber are determined from the measurement of steady pressures at the pumping time of 72 h. As a result of experiment, it is found that measured outgassing rates q obey a set of power laws of q1=c1(S/A)m1 and q2=c2(S/A)m2 where S/A is the ratio of pumping speed S to surface area A of the chamber, c1 and c2 are constants, exponents of m1 and m2 are 0.8282 for S/A≥ 10-3 ι/scm2 and 0.4655 for S/A≤ 10-3 ι/scm2, respectively. Technical application of the obtained scaling law is discussed in connection with the design of pumping system for a large vacuum device. (author)