OXYGEN DISCHARGE CLEANING METHOD FOR ALUMINUM STORAGE-RING VACUUM CHAMBERS

A discharge cleaning method using a dc plasma gun was developed to reduce photon-induced gas desorption by synchrotron radiation in electron storage rings. Hydrocarbon contaminations adsorbed on the inside surface of a long aluminum vacuum chamber (2.5 m) were removed by an oxygen plasma produced by an arc discharge. The plasma density and electron temperature were about 10(9) cm-3 and 1 eV, respectively, near the inside wall of the vacuum chamber at a discharge current of 5 A. The discharge cleaning was applied for 1 h to an aluminum vacuum chamber manufactured by the EX-extrusion process. The results were as follows: (1) measurements with a quadrupole mass spectrometer determined that 6 X 10(19) CO molecules coming from the hydrocarbon contaminations were removed by the discharge cleaning, (2) in situ Auger electron spectroscopy showed that carbon on the surface of an aluminum sample piece was removed within 1 h of discharge cleaning and (3) the photodesorption yield of the chamber with the discharge cleaning was one order of magnitude smaller than that without cleaning.