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Plasma Cleaning A new method of ultra-cleaning detector cryostats

Plasma Cleaning A new method of ultra-cleaning detector cryostats. Sebastian Deiries, Armin Silber, Olaf Iwert, Evi Hummel, Jean Louis Lizon European Southern Observatory ESO ( http://www.eso.org ). Introduction. Why cleaning of CCD cryostats?

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Plasma Cleaning A new method of ultra-cleaning detector cryostats

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  1. Plasma CleaningA new method of ultra-cleaning detector cryostats Sebastian Deiries, Armin Silber, Olaf Iwert, Evi Hummel, Jean Louis Lizon European Southern Observatory ESO (http://www.eso.org) SDW2005: Plasma Cleaning S. Deiries, ESO

  2. 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 SDW2005: Plasma Cleaning S. Deiries, ESO

  3. Conventional Cleaning • Before plasma cleaning can be applied, the piece or cryostat should roughly be clean. Normally we apply our standard cleaning processes: • mechanicalcleaning, • ultrasonic cleaning with special • detergents, • chemical cleaning with isopropyl • alcohol or acetone • baking in vacuum oven Chemicals and detergents for ultrasonic and chemical cleaning Precautions and careful handling of the chemicals Baking of cryostat parts in the vacuum oven depending from the material up to 160 o C Cryostat part in ultrasonic bath (See also “Ultra-clean CCD Cryostat – CCD contamination can be kept under control” from S. Deiries, SDW2002) SDW2005: Plasma Cleaning S. Deiries, ESO

  4. Cryostat components after conventional cleaning My colleague Armin Silber had the idea to introduce Plasma cleaning as a final ultra cleaning step: Because cryostat looks clean after conventional cleaning: but there are still (organic) contaminations on the surface. SDW2005: Plasma Cleaning S. Deiries, ESO

  5. Plasma cleaning process Application: Removal of very thin films of oil, oxides and greases • During plasma cleaning the surface is cleaned • physically by ion bombardment (like sand-blasting) • chemically e.g. by active oxygen (oxidation and reduction). SDW2005: Plasma Cleaning S. Deiries, ESO The surface is cleaned physically by ion bombardment and UV radiation and chemically by active oxygen. The surface is cleaned physically by ion bombardment and UV radiation and chemically by active oxygen.

  6. Realization of Plasma cleaning Existing vacuum oven, refurbished to a plasma oven SDW2005: Plasma Cleaning S. Deiries, ESO

  7. SDW2005: Plasma Cleaning S. Deiries, ESO

  8. High voltage plasma controllerLFG40 from company Diener http://www.dienerelectronic.de High voltage control Plasma control Pressure regulation 0.1 – 1 mBar Voltage display Plasma regulation SDW2005: Plasma Cleaning S. Deiries, ESO

  9. Plasma cleaning devices Modified vacuum oven, equipped with a high voltage anode Powerful dry vacuum pump:Alcatel ACP28 High voltage plasma controller LFG40 SDW2005: Plasma Cleaning S. Deiries, ESO

  10. Use 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 SDW2005: Plasma Cleaning S. Deiries, ESO

  11. Special arrangement: Plasma Cleaning inside everyassembled cryostat High Voltage Anodemounted outside on the cryostat window Controller Diener Electronic LFG40 Cryostat No disassembly necessary ! Trans-former (Diener) Ground cablefixed at the case SDW2005: Plasma Cleaning S. Deiries, ESO

  12. Plasma cleaning devices Successful 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! SDW2005: Plasma Cleaning S. Deiries, ESO

  13. OmegaCam cryostat during plasma cleaning SDW2005: Plasma Cleaning S. Deiries, ESO

  14. Videofrom Plasma ignition and cleaning SDW2005: Plasma Cleaning S. Deiries, ESO

  15. Safety measures • Exhaust gases should not go to the working laboratory (small toxic risk) • UV radiation is absorbed by oven window • Electrical safety SDW2005: Plasma Cleaning S. Deiries, ESO

  16. Plasma cleaning costs Procurement costs: Vacuum oven ~8000 EUR Diener Electronic LFG40 Plasma Controller ~5000 EUR Vacuum pump 7000 EUR Maintenance: Electrical costs per cleaning process 0.20 EUR Costs of special gases ~200 EUR per annum Maintenance >100 EUR per annum SDW2005: Plasma Cleaning S. Deiries, ESO

  17. Materials cleaned by plasma (Coated) Epoxy fiber glass Gold plated copper PCBs Aluminum Stainless steel SDW2005: Plasma Cleaning S. Deiries, ESO

  18. Limitations with plasma cleaning • 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? SDW2005: Plasma Cleaning S. Deiries, ESO

  19. How to handle plasma cleaned parts A plasma cleaned cryostat part must be handled strictly under clean-room condition to avoid recontamination. SDW2005: Plasma Cleaning S. Deiries, ESO

  20. Test of cleaning result • 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. contaminated Plasma cleaned SDW2005: Plasma Cleaning S. Deiries, ESO

  21. Test of cleaning result • End vacuum 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 SDW2005: Plasma Cleaning S. Deiries, ESO

  22. Test of cleaning result: • Mass-spectrum test: Water Many lines disappear or are reduced significantly CO CO2 O2 SDW2005: Plasma Cleaning S. Deiries, ESO

  23. Conclusions • Very effective cleaning of (hidden) contaminants as an addition to conventional cleaning • Fast Cleaning method • Successful cleaning of assembled cryostats (OmegaCam) SDW2005: Plasma Cleaning S. Deiries, ESO

  24. Many Thanks for Listening SDW2005: Plasma Cleaning S. Deiries, ESO

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