Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cleaning Strategies for Storage Rings Ron Reid Group Leader, Vacuum Science Group ASTeC CCLRC Daresbury Laboratory Warrington WA4 4AD, UK rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 1 of 12 Why Clean Storage Ring Vacuum Vessels? • To ensure maximum transmission of particles by reducing beam-gas scattering • Lifetime limit better than other processes • To reduce scattered radiation for health & safety (bremsstralüng) • To minimise conditioning time rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 2 of 12 Vacuum System Design Issues • The Vacuum Engineer should consider the following at the design stage: • How all parts can be cleaned (initially and in service) • Component level clean • Full assembly clean • Sub-assembly clean • Cleaning Plant Trapped Areas Solvent Trapping • Size • Robustness • Handling/Risks rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 3 of 12 Vacuum System Design Issues • Material choice • Porosity • Effect of cleaning on tolerances • Multiple materials • Varying effects of cleaning process • Risk of electro-chemical action (galvanic cell) • Assessment of cleaning effectiveness rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 4 of 12 Requirements for UHV/XHV • Minimise desorption • Remove ‘contaminants’ (i.e. components with high outgassing/vapour pressure) • Deplete reservoirs • Bulk gases • Surface overlayers (e.g. adventitious graphite) • Provide barriers • Bulk diffusion rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 5 of 12 How do we know if a surface is clean? • Phenomenologically • Measure outgassing (thermal desorption) • Measure stimulated desorption (according to requirements of system) • In each case total and partial pressure measurements useful • Characterise surfaces • Surface analysis rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 6 of 12 A Distinction • Differentiate between • Cleaning • Removal of unwanted components • Passivation • Formation of barriers • Low sticking probabilities rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 7 of 12 Some examples of cleaning processes • Solution • Water based • Solvent based • Alcohols • Chlorinated hydrocarbons • Detergents • Etchants • Acids • Alkalis • Vacuum Baking/Firing rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 8 of 12 Some examples of passivation • Air Baking • Electropolishing • Glow Discharge • But note that all of these have some cleaning effect! rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 9 of 12 Some actual cleaning processes rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 10 of 12 Results: Stainless steel contaminated then cleaned Aqueous based detergent Hydrofluoroether solvent rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 11 of 12 Acknowledgements • Joe Herbert • Keith Middleman rjr ALBA Workshop, Barcelona, 12-13th Sept 2005 12 of 12