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Titanium Nitride Coating by Reactive DC Magnetron Sputtering as a Multipactor Suppressor on Coupler RF Ceramic Windows Walid KAABI Anti e - Cloud Coatings- AEC’09 Laboratoire de l’Accélérateur Linéaire
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CERN- Octobre 12th 2009 2 Power coupler for superconductive cavities Power coupler have 3 functions to fulfil: Electromagnetic role Vacuum barrier Thermal interface Principle and Functions
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CERN- Octobre 12th 2009 3 Power coupler for superconductive cavities Coupler Design: example of TTF-III Model RF Source Cavities Cryogenic module TTF-III is the baseline solution for the future XFEL linac in DESY. In this framework, our laboratory is responsible of the RF conditioning task of 800 TTF-III couplers.
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CERN- Octobre 12th 2009 4 Power coupler for superconductive cavities Coupler Ceramic Windows Cold windows (Ø = 47 mm, h= 48 mm) Warm windows (Ø = 75 mm, h= 57 mm) Windows made of Alumina ceramic (97.6% Al 2 O 3 ): Mechanical and dielectric strength High thermal stability Low out-gazing rate High Secondary Electron Emission Yield (SEY)
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CERN- Octobre 12th 2009 5 Multipactor phenomenon RF Field + Best conditions for Multipactor phenomenon occurring: Electron-avalanche discharge + High vacuum Conditions of occurring
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CERN- Octobre 12th 2009 6 Multipactor phenomenon Multipactor phenomenon may cause damages in ceramic windows: Creation of damaging arcs, Surface overheating that may lead to surface evaporation, Load mismatch causing dangerous power reflection to the RF source. Necessity of suppression, or at least limitation of this effect Solution: decrease Alumina’s SEY by surface coating with multipactor suppressor thin layer: Titanium Nitride Damages caused in ceramic windows
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CERN- Octobre 12th 2009 7 Multipactor suppressor thin film TiN is characterised by a low SEY that remain stable on RF operational conditions
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CERN- Octobre 12th 2009 8 Multipactor suppressor thin film DC Reactive Magnetron Sputtering of TiN
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CERN- Octobre 12th 2009 9 TiN sputtering system Titanium target Rotating magnet pack Shield Rotating magnet shape = Plasma shape Rotating sample holder Sputtering machine overview
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CERN- Octobre 12th 2009 10 TiN sputtering system Sample holder motion
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CERN- Octobre 12th 2009 11 Practical guidances Ceramic window exposure to RF field induce some additional constraints: Stoichiometry control: the layer can get the multipactor suppressor property (XRD analyses ), Thickness control: deposit should be thick enough to reduce multipactor, but not so much to prevent increasing RF power reflection in ceramic surface (X-Ray reflectivity Analyses, in addition to Quartz Crystal Microbalance monitoring). Deposits made on 10x10mm quartz substrates, Use of multi-sample holder.
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