Transcript Cleaning Strategies

Cleaning Strategies for
Storage Rings
Ron Reid
Group Leader, Vacuum Science Group
ASTeC
CCLRC Daresbury Laboratory
Warrington WA4 4AD, UK
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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
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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
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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
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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
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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
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A Distinction
• Differentiate between
• Cleaning
• Removal of unwanted components
• Passivation
• Formation of barriers
• Low sticking probabilities
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Some examples of cleaning processes
• Solution
• Water based
• Solvent based
• Alcohols
• Chlorinated hydrocarbons
• Detergents
• Etchants
• Acids
• Alkalis
• Vacuum Baking/Firing
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Some examples of passivation
• Air Baking
• Electropolishing
• Glow Discharge
• But note that all of these have some cleaning
effect!
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Some actual cleaning processes
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Results: Stainless steel contaminated then
cleaned
Aqueous based detergent
Hydrofluoroether solvent
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Acknowledgements
• Joe Herbert
• Keith Middleman
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