worried about nothing? - science and technology … · · 2017-01-17worried about nothing?...

Worried About Nothing?Worried About Nothing? Measurement and Safety in

Vacuum Practice

Cleaning Components of Vacuum Systems

Joe Herbert and Keith MiddlemanVacuum Science Group

ASTeC Daresbury Laboratory (CLRC)

March 25th-26th 2003 IoP Congress - Edinburgh

Introduction

ASTeC = Accelerator Science and Technology CentreAccelerator Physics (11)Insertion Devices and Magnet Physics (7)Radio Frequency and Diagnostics (8)Vacuum Systems (5)Geodesy & Alignment (0)

Vacuum Science GroupProvides the ‘Vacuum’ design and specification for ASTeC projects.Research Programme (E.G. Cleaning, NEG, Characterisation of Materials, Evaluation of Equipment)


Outline of Presentation

(1) Why Do We Need To Clean for Vacuum?

(2) Vacuum System Design Issues

(3) Simple Cleanliness Checks

(4) More Extensive Testing

(5) Science of Cleaning

(6) Problems Associated with Large Scale Facilities

(7) Search for New Cleaning Procedures

Joe Herbert

Keith Middleman


(1) Why Do We Need To Clean For Vacuum?

We Don’t! NecessarilyIt Depends Upon What We Need Vacuum For

Vacuum Regime Required (Type of Flow)Ultimate PressureLeak RateCleanliness

∴ “To Clean or Not To Clean” & “Degree of Cleanliness”

⇒ Depends upon Application!


Examples

Irrespective of application - Manufacturer Desires Attractive Appearance!

Characteristics of a Surface (Surface Properties) altered by ‘Contamination’ at the Surface.

Process Poisoned by ‘Contaminants’

Quality of an In-Vacuum Process Severely Affected By Presence of ‘Contaminant’ Gas Phase Molecules

!

‘Contaminant’ - What is a contaminant in one application may be an essential constituent of another!


Why Clean for - Accelerator Vacuum Systems

Transport of Particles and EM RadiationLoss Reduction

Reduce Scattered Radiation for Health & Safety

Maintain Clean In-Vacuum SurfacesPrevent Particle Target PoisoningMaintain Efficient Optical Properties for EM Radiation Transport

To Provide a Controlled Atmosphere


(2) Vacuum System Design Issues

The Vacuum Engineer Should Consider the Following at the Design Stage:

How All Parts Can Be Cleaned (Initial and In Service)Component Level CleanFull Assembly CleanSub-Assembly Clean

Cleaning PlantSizeRobustnessRisks/Protection Methods

Trapped AreasSolvent Trapping


Vacuum Design Issues

Material ChoicePorosityEffect of cleaning on toleranceMultiple Materials

Varying Effects from Cleaning ProcessRisk of Electro-chemical cell

Assessment of Cleaning Effectiveness


(3) Simple Cleanliness Checks

Visual Inspection (use of hand lens)Solvent TrapsDirt TrapsSurface RoughnessStreaking / Marking / Spotting

SmellOilsCleaning Fluids

RubbingSessile Drop

Oils/Greases


(4) More Extensive Testing - A

Surface Analysis Techniques (Detailed Surface Composition)

AES - Auger Electron Spectroscopy

SIMS - Secondary Ion Mass Spectrometry

Scanning Electron Micrograph

LIMA - Laser Ionisation Mass Analysis


More Extensive Testing - B

Phenomenological Testing (Surface Vacuum Performance)

Total Outgassing Desorption

Partial Outgassing Desorption

Stimulated Desorption

Friction

Electron Induced

Ion Induced

Thermal

Process Stimulated


Application for Storage Ring Vacuum Systems

UHV Total Pressures Required ~ 1x10-9 mbarMaintain Satisfactory Lifetime Stored Electron Beam

Low Presence of High Mass SpeciesElectron Scatter ∝ Atomic Number2

Hydrocarbons < 1%Pump Lubricants < 0.1%

Phenomenological Comparison Testing is EmployedCompare Total and Partial Pressures with Standard ValuesElectron Stimulated Desorption (ESD) Comparisons

Simulation for Photon Stimulated Desorption (PSD)



Keith Middleman to continue………..



Vacuum is limited by the materials used and how they are prepared.

For UHV we need to have ‘clean’ surfaces

Bakeout


Science of CleaningSolvent - A solvent is a substance that dissolves another substance or substances to form a solution (a homogeneous mixture). The solvent is the component in the solution that is present in the largest amount or is the one that determines the state of matter (i.e. solid, liquid, gas) of the solution.

Surfactants - surface active agent

Hydrophobe

Hydrophile


Science of Cleaning

Penetrating and Wetting agents Surfactants which change the chemical composition of the hydrophobic

and hydrophilic ends of the molecule, this opens up the possibility of

Detergency Foaming Emulsifying Solubilising Dispersing

Chelators - remove the hardness in water

Saponifiers - convert animals fats into natural soaps


Cleaning Techniques

Physical Methods Blowing Bead Blasting Dry Ice cleaning Cutting and Grinding Polishing

Passivation - techniques which reduce outgassing Oxide films Nitride coatings (TiN, BN) Active films (NEG coatings)


Cleaning Techniques

Special Cleaning Techniques Ultrasonic cleaning - widely used

Electropolishing Glow discharge Air Baking Chemical Baking

Heaters

Surface

Ultrasonic Waves

Cavitation bubbles

Contaminant

Passivation


Typical Cleaning AgentsAgent Examples Advantages Disadvantages DisposalWater Cheap, readily

availableNeed de-min for cleanliness.

Not a strong solventTo foul drain

Alcohols Ethanol,methanol, iso-

propanol

Relatively cheap andreadily available.

Quite good solvents

Need control – affect workers;some poisonous; some

flammable; stringent safetyprecautions.

Evaporate or controlleddisposal.

OrganicSolvents

Acetone, ether,benzene

Good solvents,evaporate easily with

low residue.

Either highly flammable orcarcinogenic

Usually evaporate

CFC’s FreonTM

(CFC-113)Excellent solvents;

evaporate easily withlow residue

Banned Strictly controlled, mustnot be allowed to

evaporate

Chlorinatedhydrocarbons

Trichloroethylene (TrikeTM)

Excellent solvents.Non-toxic. Low boiling

point. Low residue

Trike may be banned. Toxic,require stringent safety

precautions.

Strictly controlled

Detergents Aqueous solutions,non toxic. Cheap and

readily available.Moderate solvents.

Require careful washing anddrying of components. Can

leave residues.

To foul drain anddilution

Alkalinedegreasers

AlmecoTM,sodium

hydroxide

Aqueous solutions,non- toxic. Moderate

solvents

Can leave residues and maythrow particulate precipitates

Requiresneutralisation, thendilution to foul drain.


SRS Cleaning Procedure

SR S A N K A BESSY II

Hot w ater jet w ith detergent Coarse cleaning with Chesterton(KPC820)

W ipe off surface dirt

Surface stripping with alum inabeads

Rinse in hot de-m in w ater U ltrasonic w ith trichloroethane

Ultrasonic wash in hot Triklone Ultrasonic wash in hot P3-Alm eco 18

Treatm ent w ith hotperchloroethylene (120°C)

Vapour W ash in hot Triklone Rinse in de-m in water Ultrasonic cleaning in hot P3-A lm eco 18 for 10 m inutes.

R inse w ith de-m in water D ry in warm dust free air, bagand seal.

R inse for 15 m inutes w ith tapw ater.

Im m erse in hot alkaline bath ofP3-Alm eco 36 at 60°C

W ash in hot de-m in w ater for 90m inutes.

R inse in de-m in water Open air drying and cooling ofcom ponents.

Dry in w arm , dust free air, bagand seal.


(6) Problems with Large Scale Cleaning FacilitiesUltrasonic Bath


Problems with Large Scale Cleaning FacilitiesVapour wash


Problems with Large Scale Cleaning FacilitiesWater Jet and Detergent Phase


Problems with Large Scale Cleaning Facilities

Drying Oven Personal Exposure Monitor



COSHH Assessment - Health and Safety

Risk Assessment - every procedure

Storage of Chemicals - Special bunded areas

Environmental issues - correct removal

Monitoring Systems - personal and atmospheric

Legislation



Current LegislationVienna Convention - 1985Montreal Protocol - 1987

Amendments - most recent 2000 Protection of the Ozone Layer CFC’s HCFC’s Carbon Tetrachloride Methyl Chloroform Other halogenated hydrocarbons

Why Change?Reclassification of 1,1,2-Trichloroethylene (TrikeTM)

Improved Health and Safety regulations


(7) Replacement of 1,1,2-Trichloroethylene

What is important to us?Thermal outgassing and ESDThroughput method of measuring outgassing rates

Comparative Tests - existing procedure proven for 20 years

Pump

P1 P2

Conductance, C

Sample

Q = P1 - P2A

C


Outgassing Measurement Facility


Thermal Outgassing Results

Experiment Total outgassingrate (mbar

l/s/cm2)

Net outgassing rate(mbar l/s/cm2)

Blank Run 1.97 x 10-12 -

Noncontaminatedsample run

2.35 x 10-12 3.76 x 10-12

Contaminatedsample run

6.57 x 10-12 4.6 x 10-12

Contaminatedsample run

through n-propylbromide

1.22 x 10-11 1.023 x 10-11


Future Possibilities

Other solvents Further n-propyl bromides Non flammable ethers

Aqueous systems e.g. Micro 90


Conclusions

The level of vacuum required or the process determines the standard of cleanliness required.

Vacuum is often limited by the surface properties of the materials used.

Various methods used to condition materials for vacuum.

There is no one defining cleaning process that works

worried about nothing? - science and technology … · · 2017-01-17worried about nothing?...

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