Abstract
Thermal outgassing rate measurements and residual gas analyses were used to study two aluminum-alloy chambers, which had different surface treatments. One chamber was machined with alcohol, and the other was extruded by using a diamond-tip die to provide smooth internal surface . The effect of surface roughness on the outgassing rate and the mechanism of the slope -2 in outgassing rate curve were investigated in this work. The chambers were vented to dry nitrogen atmospheres with different venting conditions in order to obtain lower outgassing rates. The results showed that in the experiments of venting to extremely with a humidity of dry nitrogen gas(1.3ppb), to protect the vacuum chamber from atmosphere environment by glove box, had the lowest outgassing rate among the others. The outgassing rates of the extruded aluminum chamber at the 1st,10th and 24th hour were shown as q1=1.6x10-11 mbar.L/s.cm2, q10=6.0x10-13 mbar.L/s.cm2 and q24=1.6x10-13 mbar.L/s.cm2,which were 1.5,5.5 and 10 times relatively lower than the chamber cleaned with alcohol. It was shown that the environmental humidity had a great effect on the outgassing rate. From the results of the outgassing rate curve, the slope of the alcohol treated aluminum chamber was -2 .1 at the first hour after pumping and the slope of the ex-treated aluminum chamber was -1.8. In summary, the results from this research implied that the mechanism of the slope -2 of the outgassing rate curve has relations with the surface porosity and the gas dissociation.