-
Author(s):
K. Akaishi, Y. Kubota, K. Ezaki and O. Motojima
-
Title:
Experimental Study on Scaling Law of Outgassing Rate with A Pumping Parameter
Date of publication:
Aug. 1994
-
Key words:
outgassing rate, ultimate pressure, pumping parameter, LHD
-
Abstract:
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 l/s. 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 degrees C 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 q_1=c_1 (S/A)^m1 and q_2=c_2 (S/A)^m2 were S/A is the ratio of pumping speed S to surface area A of the chamber, c_1 and c_2 are constants, exponents of m_1 and m_2 are 0.8282 for S/A geq 10^-3l/s cm^2, and 0.4655 for S/A leq 10^-3 l/scm^2, respectively. Technical application of the obtained scaling law is discussed in connection with the design of pumping system for a large vacuum device.
-
|
