cleaning for ultra- high vacuum (uhv) · outline of presentation zuhv limiting factors zwhy do we...
TRANSCRIPT
![Page 1: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/1.jpg)
Cleaning for Ultra-High Vacuum (UHV)
Keith MiddlemanVacuum Science Group
ASTeCCCLRC Daresbury Laboratory
![Page 2: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/2.jpg)
Outline of Presentation
UHV Limiting Factors
Why Do We Need To Clean for Accelerators?
Methods to Reduce Outgassing
SRS Cleaning Procedure
Methods of Testing
Search for New Cleaning Solvents
![Page 3: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/3.jpg)
Limiting Factors for achieving UHV
Material ChoiceGas Sources
Contaminant: prevents vacuum system reaching required base pressure or introduces unwanted species into the residual gas.Outgassing: The outgassing rate is the time-dependent rate at which gases and vapours are released under vacuum. This limits the ultimate pressure achievable and can introduce contamination into the vacuum system.
![Page 4: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/4.jpg)
Why Clean for Accelerator Vacuum Systems?
UHV Total Pressures Required ~ 1x10-9 mbarMaintain Satisfactory Lifetime Stored Electron Beam
Electron Scatter ∝ Atomic Number2
Low presence of high mass speciesHydrocarbons < 0.1% Pump Lubricants < 0.01%
Stimulated desorptionElectron or Ion induced - Major gas sourceDesorption Yield (Number of molecules per incident photon)
Maintain Clean In-Vacuum SurfacesPrevent Particle Target PoisoningMaintain Efficient Optical Properties for EM Radiation Transport
![Page 5: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/5.jpg)
Methods to Reduce Outgassing
Bakeout - If the pressure is not low enough we can reduce the thermal outgassing rates by reducing the surface coverage N or the temperature T.
Beam Cleaning
Passivation Oxide films Nitride coatings (TiN, BN) Active films (NEG coatings)
![Page 6: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/6.jpg)
Methods to Reduce Outgassing
Ultrasonic Cleaning - widely used
Glow discharge
Electropolishing
![Page 7: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/7.jpg)
SRS Cleaning Procedure
EX-SITU BAKEOUT
Leak check (< 10-10
Bake to 250°C for 24 hours
Record RGA scan
Effective pre-treatment ensures outgassingare reduced to < 10l s-1 cm-2
CLEANING PROCEDURE
Hot water jet with detergentSurface stripping with alumina beadsUltrasonic wash in hot Triklone
Vapour Wash in hot TrikloneRinse with de-min waterImmerse in hot alkaline bath of P3-Almeco 36 at 60°CRinse in de-min waterDry in warm, dust free air, bag and seal.
mbar l s-1)
rates -11 mbar
![Page 8: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/8.jpg)
Cleaning FacilitiesWater Jet and Detergent Phase
![Page 9: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/9.jpg)
Cleaning FacilitiesVapour wash
![Page 10: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/10.jpg)
Testing - Is it ‘Clean’?
Surface Analysis Techniques (Detailed Surface Composition)
AES - Auger Electron Spectroscopy
SIMS - Secondary Ion Mass Spectrometry
Scanning Electron Micrograph
Phenomenological Testing (Surface Vacuum Performance)Measure Total Outgassing Rates - Total Pressure Gauge
Measure Partial Pressures - RGA
Stimulated Desorption (Friction, Electron or Ion Induced, Thermal)
![Page 11: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/11.jpg)
Replacement of 1,1,2-Trichloroethylene
Why Change? - Reclassification of 1,1,2-Trichloroethylene (TrikeTM)
What is important to us? - Thermal outgassing and ESD
Throughput method of measuring outgassing rates
CA
PPQ ⋅−
=21
Comparative Tests - existing procedure proven for 20 years
![Page 12: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/12.jpg)
Outgassing Measurement Facility
![Page 13: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/13.jpg)
Thermal Outgassing Results
Experiment Information Thermal Outgassing Rate Q (mbar l s-1cm-2)
Blank Run 9.3E-14 No Contamination Cleaned with Trike 7.9E-13 Full Contamination. Cleaned with Trike 9.3E-13 Full Contamination. Cleaned with Lenium 2.8E-12 Full Contamination. Cleaned with Leksol 9.3E-14 Full Contamination. Cleaned with Novec HFE 7.5E-13 Full Contamination. Cleaned with IPA 7.5E-13 Full Contamination. Cleaned with Micro 90 3.7E-13 Full Contamination. Cleaned with Lancerclean 4.6E-12
![Page 14: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/14.jpg)
RGA Data - Thermal Outgassing
Acceptable UHV ScanHydrocarbon < 0.1%Pump lubricants < 0.01%
Unacceptable UHV ScanHydrocarbon ~ 25%Pump lubricants ~ 5%
![Page 15: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/15.jpg)
RGA Data - Electron Stimulated Desorption
Desorption Yield ~ 10-3 molecules / e-
Desorption Yield ~ 4 molecules / e-
![Page 16: Cleaning for Ultra- High Vacuum (UHV) · Outline of Presentation zUHV Limiting Factors zWhy Do We Need To Clean for Accelerators? zMethods to Reduce Outgassing zSRS Cleaning Procedure](https://reader031.vdocuments.mx/reader031/viewer/2022030822/5b37da3f7f8b9a5a178cc368/html5/thumbnails/16.jpg)
Summary
Accelerators (storage rings) require UHV
Need to minimise thermal outgassing and stimulated desorption
Requires a detailed cleaning recipe
Phenomenological Testing