Comparison of chemical cleaning methods of aluminum alloy vacuum chambers for electron storage rings

Abstract

Three chemical precleaning methods suitable for aluminum alloy vacuum chambers for electron storage rings have been compared. The methods ranged from vapor degreasing with no chemical attack to light alkaline etching and strong alkaline etching in NaOH. The techniques used to evaluate and compare the three treatments included Auger analysis, thermal outgassing, electron and x-ray induced neutral gas desorption, argon glow discharge cleaning, and scanning electron microscope examination of the surface. In general, the NaOH treatment was best followed closely by the light alkaline etch and then the vapor degreasing. A variant of the light alkaline etch method was used to clean the 2000 Al vacuum chambers of the CERN large electron positron storage ring project. Two chambers cleaned by this method were exposed to synchrotron radiation in a dedicated beam line of a synchrotron radiation source. Compared to a reference chamber cleaned by NaOH these two chambers were initially worse, but after 1 A h of machine operation the difference practically vanished.