SURFACE CHARACTERISTICS OF ALUMINUM AND OF SEVERAL METALS FROM VIEW POINT TO REDUCE DYNAMIC GAS DESORPTION

摘要

Dynamic gas desorption, especially photon stimulated gas desorption in e(-) (or e(+)) storage rings is influenced by characteristics of surface oxide and contamination. Photoelectrons decompose water and hydrate in the oxide layer. The resultant hydrogen deteriotates pressure. Harmful molecules on beam lifetime are CO, CO2, H2O, CH4, and other hydrocarbons. The elements are chemically decomposed products in the surface layer. Therefore water, hydrates and hydroxides in the oxide layer must be removed and changed to pure oxide. The experiments to support this idea are reviewed: deterioration in hydrogen gas desorption in sputter ion pump (5 keV) with Al hydroxide. Removal of surface contamination by ion beam etching but not by discharge cleaning. Detection of deuterium desorption by e(-) bombardment (3.5 keV) from alkaline etched aluminum but not from EX heated Al. Al2O3, SiO2 and Cr2O3 are stable against synchrotron radiation (similar to 100 keV) in ultra pure water, but not Ni oxide and Cu oxide. The oxides like Al2O3 and Nb2O5 made by ozone treatment improved the gas desorption characteristics (epsilon(c) = 26 keV), and high Q and high field gradient (14.4 MeV//m) characteristics of a superconducting Nb cavity, respectively. [References: 17]