Plasma Cleaning A new method of ultra-cleaning detector cryostats
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Transcript of Plasma Cleaning A new method of ultra-cleaning detector cryostats
20. June 2005 SDW2005: Plasma Cleaning S. Deiries, ESO
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Plasma CleaningA new method of ultra-cleaning
detector cryostats
Sebastian Deiries, Armin Silber, Olaf Iwert,
Evi Hummel, Jean Louis LizonEuropean Southern Observatory ESO (http://
www.eso.org)
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Introduction
• Why cleaning of CCD cryostats?• Contamination is more a problem with optical than IR
detectors blue wavelengths• Conventional cleaning (mechanical, with detergent,
isopropyl-alcohol, acetone & baking) insufficient?• Plasma cleaning used in industry for ultra cleaning• It is a simple method with easy installation:
First results after a few days!• It is rather cheap and has very low cleaning costs• It gives very high efficient cleaning results• The risks are low
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Conventional CleaningConventional Cleaning
(See also “Ultra-clean CCD Cryostat – CCD contamination can be kept under control” from S. Deiries, SDW2002 )
Cryostat part in ultrasonic bath
Baking of cryostat parts in the vacuum oven depending from the
material up to 160 o C
Chemicals and detergents for ultrasonic and chemical cleaning Precautions and
careful handling of the chemicals
Before plasma cleaning can be applied, the piece or cryostat should roughly be clean. Normally we apply our standard cleaning processes:
• mechanicalmechanical cleaning, • ultrasonic ultrasonic cleaning with special detergents, • chemical chemical cleaning with isopropyl alcohol or acetone• bakingbaking in vacuum oven
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Cryostat components after Cryostat components after conventional cleaningconventional cleaning
Because cryostat looks clean after conventional cleaning: but there are still (organic) contaminations on the surface.
My colleague Armin Silber had the idea to introducePlasma cleaning as a final ultra cleaning step:
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Plasma Plasma cleaningcleaning process process
During plasma cleaning the surface is cleaned• physicallyphysically by ion bombardment (like sand-blasting)• chemicallychemically e.g. by active oxygen (oxidation and reduction).
Application: Removal of very thin films of oil, oxides and greases
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Realization of Plasma cleaningRealization of Plasma cleaning
Existing vacuum oven, refurbished to a plasma oven
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High voltage High voltage plasma controllerplasma controller
LFG40 from company DienerLFG40 from company Diener
Plasma control
High voltage control
Pressureregulation
0.1 – 1 mBarVoltage display
Plasma regulation
http://www.dienerelectronic.dehttp://www.dienerelectronic.de
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Plasma cleaning devicesPlasma cleaning devices
Modified vacuum oven, equipped with a high voltage anode
Powerful dry vacuum pump:Alcatel ACP28
High voltage plasma controller LFG40
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Use of different gasesUse of different gases
• Oxygen - Best for cleaning of aluminium and stainless steel
• Ambient air - Sufficient for normal cleaning
• Argon - Cleaning without chemical reaction
• Hydrogen - Best for cleaning of gold, silver and copper
• Nitrogen - Similar as Argon
• Flour-containing gases - Chemical cleaning
• Mixtures of the gases mentioned above
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Special arrangement: Special arrangement: Plasma Cleaning inside everyPlasma Cleaning inside every
assembled cryostatassembled cryostat
Trans-former
(Diener)
High Voltage Anodemounted outside on the cryostat window
Ground cable fixed at the case
Controller Diener
Electronic LFG40
CryostatNo
disassembly necessary !
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Plasma cleaning devicesPlasma cleaning devicesSuccessful plasma cleaning inside the assembled OmegaCam cryostat
After some minutes the large volume (approx. 200 l) of the cryostat was filled by a violet glowing plasma. A normal cleaning process takes not longer than 10 minutes!
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OmegaCam cryostat during plasma cleaningOmegaCam cryostat during plasma cleaning
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VideoVideofrom Plasma ignitionand cleaning
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Safety measuresSafety measures
• Exhaust gasesExhaust gases should not go to the working laboratory (small toxic risk)
• UV radiationUV radiation is absorbed by oven window
• Electrical safetyElectrical safety
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Plasma cleaning costsPlasma cleaning costs
Procurement costs:Vacuum oven ~8000 EURDiener Electronic LFG40 Plasma Controller ~5000 EURVacuum pump 7000 EUR
Maintenance:Electrical costs per cleaning process 0.20 EURCosts of special gases ~200 EUR per annumMaintenance >100 EUR per annum
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Materials cleaned by plasmaMaterials cleaned by plasma
(Coated) Epoxy fiber glass
Gold plated copper
AluminumStainlesssteel
PCBs
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Limitations with plasma Limitations with plasma cleaningcleaning
• Plastic materials and PCBsshould not be plasma-treated longer than 10 minutes; risk of becoming black
• Damage of CCD detectors?Test ongoing; which of the manufacturer present at the SDW2005 is interested and would supply a sample CCD?
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How to handle plasma How to handle plasma cleaned partscleaned parts
A plasma cleaned cryostat part must be handled strictly under clean-room condition to avoid recontamination.
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Test of cleaning resultTest of cleaning result
• Water drop method:Water drop method:
A sample, which is contaminated shows a round water drop on its surface. After the plasma cleaning there is less adhesion, therefore no water drop on the surface possible: the water is flowing away.
contaminatedPlasma cleaned
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Test of cleaning resultTest of cleaning result
• End End vacuumvacuum test: test:
Typical vacuum end pressure values of ESO standard cryostats (after 1h pumping time):
Before plasma cleaning: 1 x 10E-3mBar
After plasma cleaning: 5x 10E-5mBar
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Test of cleaning result:Test of cleaning result:
Many lines disappear or are reduced significantly
• Mass-spectrum test:Mass-spectrum test:
Water
COO2 CO2
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ConclusionsConclusions
• Very effective cleaning of (hidden) contaminants as an addition to conventional cleaning
• Fast Cleaning method
• Successful cleaning of assembled cryostats (OmegaCam)
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Many Thanks Many Thanks for Listeningfor Listening