Non-Evaporable Getter Coating for UHV/XHV Applications Dr. Oleg B. Malyshev Senior Vacuum Scientist ASTeC Vacuum Science Group, STFC Daresbury Laboratory, UK 11 th February 2010
Two concepts of the ideal vacuum chamber: Traditional: surface which outgasses as little as possible ( nil ideally) surface which does not pump otherwise that surface is contaminated over time Results in Surface cleaning, conditioning, coatings Vacuum firing, ex-situ baling Baking in-situ to up to 300 C Separate pumps New (NEG coated surface) surface which outgasses as little as possible ( nil ideally) a surface which does pump, however, will not be contaminated due to a very low outgassing rate Results in NEG coated surface There should be no un-coated parts Activating (baking) in-situ at 150-180 C Small pumps for C x H y and noble gases 2
Source of Gas in a Vacuum System Thermal, photon, electron or ion stimulated desorption: Vacuum Subsurface Bulk layers Molecules diffused through the bulk material (mainly subsurface layers) of the vacuum chamber, entering the surface and desorbing from it Molecules adsorbed on the surface (initially or after the air venting) and desorbing when vacuum chamber is pumped Outgassing rate depends on many factors: choice of material, cleaning procedure, pumping time, bombardment (irradiation) dose, etc... Surface Conditioning for Ultra High Vacuum
What NEG coating does A pure metal film ~1-µm thick without contaminants. Vacuum NEG Subsurface Bulk Coating Layers A barrier for molecules from the bulk of vacuum chamber. A sorbing surface on whole vacuum chamber surface Surface Conditioning for Ultra High Vacuum 4
Deposition method Cylindrical magnetron deposition Planar magnetron deposition
Region scan of XPS core levels of Ti, Zr, C and V of a Ti-Zr-V film (surface composition and chemical bounding)
RBS (film compositions in bulk)
XRD of Ti-Zr-V film (microstructure and morphology)
Set-up for NEG pumping evaluation in ASTeC VS lab. Test chamber 1 (option)
ASTeC activation procedure
NEG pumping properties
Twisted wires vs. alloy target 1.E+00 C O s t ic k in g p r o b a b ility 1.E-01 TiZrV(twisted wires) TiZrV (alloy wire) TiZrV (alloy wire) 1.E-02 140 160 180 200 220 240 260 280 300 320 Activation temperature, o C
NEG composition: Ti, Zr, V, Hf 1 Single metal NEG coatings 1 Binary metal NEG coatings 1 Ternary and quatornaly NEG coating CO sticking probability 0.1 0.01 Ti Zr V Hf 1 10 3 140 160 180 200 220 240 260 280 300 320 10 CO sticking probability 0.1 0.01 Ti-Zr Ti-V Zr-V 1 10 3 140 160 180 200 220 240 260 280 300 320 10 CO sticking probability 0.1 0.01 Ti-Zr-V Hf-Zr-V Ti-Zr-Hf Ti-Hf-V Ti-Zr-Hf-V 3 1 10 140 160 180 200 220 240 260 280 300 320 10 CO pumping capacity [ML] 1 0.1 0.01 Ti Zr V Hf 1 10 3 140 160 180 200 220 240 260 280 300 320 0.1 CO pumping capacity [ML] 1 0.1 0.01 Ti-Zr Ti-V Zr-V 1 10 3 140 160 180 200 220 240 260 280 300 320 0.1 CO pumping capacity 1 0.1 Ti-Zr-V 0.01 Hf-Zr-V Ti-Zr-Hf Ti-Hf-V Ti-Zr-Hf-V 1 10 3 140 160 180 200 220 240 260 280 300 320 0.1 H2 sticking probability 0.01 1 10 3 Ti Zr V Hf 1 10 4 140 160 180 200 220 240 260 280 300 320 H2 sticking probability 0.01 1 10 3 Ti-Zr Ti-V Zr-V 1 10 4 140 160 180 200 220 240 260 280 300 320 H2 sticking probability 0.01 3 1 10 Ti-Zr-V Hf-Zr-V Ti-Zr-Hf Ti-Hf-V Ti-Zr-Hf-V 4 1 10 140 160 180 200 220 240 260 280 300 320 Activation temperature [ C] Activation temperature [ C] Activation temperature [ C]
Stainless steel vs TiZrV NEG coated vacuum chamber under SR
Reducing the gas desorption from the NEG coatings Main gases in the NEG coated vacuum chamber are H 2 and CH 4 H 2 can diffuse through NEG film under bombardment or heat CH 4 is most likely created on the NEG surface from diffused H 2 and C (originally from sorbed CO and CO 2 ) Therefore the H 2 diffusion must be suppressed Vacuum NEG Subsurface Bulk Coating Layers
Solution: Reducing the gas desorption from the NEG coatings The coating consists of two layers: 1 st layer is a barrier with low diffusion for the H 2 2 nd layers is usual NEG coating with columnar structure to provide good pumping Vacuum NEG Barrier Subsurface Bulk Coating Layers The resulting coating will be tested with electrons on the lab, later on SR beamline or beam vacuum chamber in accelerator
SEM images of films (film morphology ) columnar dense Best for pumping A first candidate for a barrier 22-26 September 2008 Lake Balaton, Hungary 10th European Vacuum Conference Oleg Malyshev 17
Reducing the gas desorption w/o NEG coatings Solution The coating consists of two layers: A barrier layer is a with low diffusion Vacuum Barrier Subsurface Bulk Layers for the H 2 A controlled smooth oxide layer to create smooth surface with low outgassing The resulting coating will be tested with electron on the lab, later on SR beamline or beam vacuum chamber in accelerator
New programme: electron stimulated desorption Modified NEG pumping properties evaluation rig: To measure sticking probability α To measure electron stimulated gas desorption as a function of Electron energy Dose Wall temperature (20-100 C) Activation/bakeout temperature Can be used for samples with: NEG coating Low desorption coating No coatings
Electron Bombardment e - CH 4 CO e - CO 2 H 2 Filament: Th/W, Th/Iror Y/Ir
Electron Stimulated Desorption (ESD) studies programme ESD from different materials Stainless steel Al Cu NEG coated samples Coating for low outgassing ESD as a function of Activation/bakeout temperature Electron energy Electron dose Coating density, morphology and structure
ESD: stainless steel vs non-activated NEG coated vacuum chamber
ESD: stainless steel vs activated NEG coated vacuum chamber
ESD: electron energy dependence 0.01 Stainless Steel Energy Dependance TiZrV - 160 1 10 3 yield [molecules per electron] 1 10 4 1 10 5 1 10 6 10 100 1 10 3 1 10 4 energy [ev]
ESD: self activation
Example of NEG application: ILC DR arc An aluminium tube after bakeout at 220 C for 24 hrs and 100 Ahr beam conditioning: a pump with S eff = 200 l/s every 5 m H 2, CO and CO 2 Inside a NEG coated tube after activation at 160 C for 24 hrs and 100 Ahr beam conditioning: a pump with S eff = 20 l/s every 30 m A H 2 and CH 4
Conclusions: NEG coating is a technology for UHV/XHV vacuum It is a delicate material but allows to reach XHV at lower costs. ASTeC VS group in a collaboration with MMU has improved and continue improving the NEG coatings. The knowledge and experience available for the UK vacuum industry and applications in ASTeC VS group.
Acknowledgments Co-authors: ASTeC. Dr. K.J. Middleman Mr. A.N. Hannah Mr. A. Smith Dr. S. Patel MMU. Dr. R. Valizadeh Prof. J.S. Colligon Dr. V. Vishnyakov Managerial support: Dr. R. Reid Mr. J. Herbert Prof. M. Poole