Overview of Advanced Surface Science activities at CERN. S.Calatroni, M.Taborelli TE-VSC-SCC

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1 Overview of Advanced Surface Science activities at CERN S.Calatroni, M.Taborelli TE-VSC-SCC

2 Basic components of particle accelerators Technology Department 10 October 2014 S. Calatroni & M. Taborelli 2

3 Magnets Technology Department 10 October 2014 S. Calatroni & M. Taborelli 3

4 Accelerating cavities Technology Department 10 October 2014 S. Calatroni & M. Taborelli 4

5 The world s longest vacuum system (about 100Km): - Pressure ranges down to XHV in LHC (<10-12 mbar) - Necessary to reduce the beam/gas interaction (defocussing, energy spread, lifetime, noise in the detectors of the experiments) - Pumping is achieved by mechanical pumps, ion pumps, cryopumping and getters Technology Department 10 October 2014 S. Calatroni & M. Taborelli 5

6 Particle detectors CMS ATLAS Technology Department 10 October 2014 S. Calatroni & M. Taborelli 6

7 Activities: Surfaces Chemistry and Coatings Most accelerator components require some kind of surface treatment or surface modification: Surface modification by surface finishing (UHV grade cleaning, etching, electroplating, electrochemical characterization ) Thin film PVD coating (magnetron sputtering, evaporation) Surface characterization and analysis (XPS, Auger, Secondary Electron Yield, emissivity) Chemical analysis (FTIR, UV-vis, Gas Chromatography, atomic absorption spectroscopy, DSC,.) The goal is to guarantee, maintain and improve the performance of the accelerators and detectors in terms of availability, quality, lifetime of components: research and development, prototyping, production, control Technology Department 10 October 2014 S. Calatroni & M. Taborelli 7

8 Preparing components for UHV or for subsequent treatments Technology Department 10 October 2014 S. Calatroni & M. Taborelli 8

9 Intensity [a.u.] Transmittance [%] Monitoring cleanliness for UHV components: FTIR Through elution with C 6 H 14 Transmittance [%] 4000 CH stretching of CH CH 3 asymmetric deform. of Si-CH 3 Wavenumber cm-1 CH 3 symmetric deform. of Si-CH Wavenumber [cm -1 ] C:\OPUS_NT\MEAS\OILS AND GREASES\RHODORSIL OIL; SILICONE OIL.0 solid 2003/07/ Si-C stretching and CH3 rocking Si-O-Si stretching 1000 S.Ilie, C.Petitjean, C.Dias-Soares 19%C Fe2p Cr2p O1s Stainless steel 316LN C1s XPS 28%C %C S2p P2p Binding energy [ev] Technology Department 10 October 2014 S. Calatroni & M. Taborelli 9

10 Copper plating of large objects (DTL tank) Difficult to obtain uniform plating Small ratio bath-volume to surface Final assembly with the electrodes for the accelerator Technology Department 10 October 2014 S. Calatroni & M. Taborelli 10

11 Plating of many different metals: Ag, Au, Rh on the LHC RF-contacts Rh/Cu Au/CuBe Ag/CuBe Inserted in the machine vacuum: cleanliness and purity to avoid degassing! Radiography, installed The Ag and Rh combination provides good electrical contact without cold-welding in vacuum Technology Department 10 October 2014 S. Calatroni & M. Taborelli 11

12 Current density (A/m 2 ) Optimization of current profile for the Electropolishing of Nb superconducting RF cavities (SPL) 5-cell cavity Electrode and current Simulation with smooth electrode (red) and optimized electrode (with protrusions) to get more uniform current and polishing (blue) 450 J profile - β-1-spl - optimised Standar d optimis ed Distance along anode (mm) Technology Department 10 October 2014 S. Calatroni & M. Taborelli 12

13 Coating of vacuum chambers DC-magnetron sputtering with target made of intertwisted wires of Ti, Zr, V: developed at CERN in Patented and licensed to industry Before coating after coating Activation temperature (~180 ºC) compatible with copper vacuum chambers (does not deteriorate too much the mechanical properties). Used for the LHC accelerator for pumping and low Secondary Electron Yield (d max =1.1 after activation) in 6 km of Long Straight Sections Technology Department 10 October 2014 S. Calatroni & M. Taborelli 13

14 Cylindrical Magnetron configuration General NEG TUBE B Proces Gas Ar Ar+ 3mm wires of Ti, Zr and V V Vacuum pumps Ideal for vacuum chamber that needs a coating Technology Department 10 October 2014 S. Calatroni & M. Taborelli 14

15 Coating plant for LHC LSS and detector chambers up to 7 m length Technology Department 10 October 2014 S. Calatroni & M. Taborelli 15

16 Lab size DC-magnetron sputtering facilities From small size substrates up to 1.2 m length, rotations for complex shapes Up to 3 independent targets for alloy deposition with tunable composition Typical materials: - Cu, Au - Ti - NEG (TiZrV) - Nb - B 4 C Technology Department 10 October 2014 S. Calatroni & M. Taborelli 16

17 Cylindrical configuration Internal coating of object without flanges: in vacuum chamber Ø 200 mm Ø in = 10 mm PS-booster pick-up Aegis H-bar cooling trap Technology Department 10 October 2014 S. Calatroni & M. Taborelli 17

18 High Energy and Intensity Isotope Separator On Line DEtector HIE-ISOLDE upgrade project Boost the radioactive beam energy from 3MeV/u to 10MeV/u by using SC linac. Quarter-wave resonator (QWR): Nb thin film sputtered on 3D forged OFE Cu substrate Technology Department 10 October 2014 S. Calatroni & M. Taborelli 19

19 Nb/Cu cavities: HIE-ISOLDE Substrate preparation (electropolishing or chemical polishing) are crucial for the success of the coating Technology Department 10 October 2014 S. Calatroni & M. Taborelli 20

20 Coatings preventing electron cloud + Proton bunch (charge +) Gas molecule Electron (charge -) The beam is perturbed by the electron multiplication; the problem is more important for high beam currents (beam potential) and short bunch spacing To reduce the effect one must reduce the Secondary Electron Yield of the walls or attract the generated electrons by other means Technology Department 10 October 2014 S. Calatroni & M. Taborelli 21

21 SEY The possible solution : carbon a-c coatings Dose below 10-6 Clb/mm CNe14 as recieved CNe14 after about 1 month air exposure energy [ev] -a-c coating on copper deposited by magnetron sputtering (in Ne) -as expected SEY does not change for thicknesses above 50 nm -development started in 2008 Technology Department 10 October 2014 S. Calatroni & M. Taborelli 22

22 electron gun Measurement of SEY developed in-house I p A I c I c Sample I s A I p = I s + I c SEY measurement XPS d = I c / (I s + I c ) Technology Department 10 October 2014 S. Calatroni & M. Taborelli 23

23 Intensity [a.u.] XPS: comparison with graphite C1s C1s HOPG CNe a-c(ne) HOPG cleaved in air Binding energy [ev] The C1s peak is wider than that of freshly cleaved graphite: due to the oxygen on the surface (8-10% typical) and chemical shift of C-O bonds or due to the more disordered structure and different C-C bond species? Technology Department 10 October 2014 S. Calatroni & M. Taborelli 24

24 Introduction: SPS dipoles Almost 5 km of the SPS are filled with MBB and MBA type dipoles (>700). The length of each dipole is 6.5 m and weights ~18 tons. The beampipes are embedded in the yoke. coat new beampipes, open the dipole, exchange beampipe, close the dipole. Easy to coat Too expensive (open/close dipole) coat the actual beampipes directly in the dipole. Difficult Easy to to coat coat cheaper Technology Department 10 October 2014 S. Calatroni & M. Taborelli 25

25 DC hollow cathode Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS) Graphite targets (cells) Technology Department 10 October 2014 S. Calatroni & M. Taborelli 26

26 DC hollow cathode Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS) Graphite targets (cells) MBB dipole Technology Department 10 October 2014 S. Calatroni & M. Taborelli 27

27 DC hollow cathode Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS) THE TECHNIQUE IS MATURE FOR LARGE SCALE PRODUCTION Graphite targets (cells) Pressure: 1.1 x10-1 mbar (Ar) Power: 0.9 kw 600 V) 0.5 mm in 20 hours Technology Department 10 October 2014 S. Calatroni & M. Taborelli 28

28 Research interests - Treatments or coatings to lower the SEY of insulator surfaces, like alumina, and metals - NEGs with lower activation temperature than TiZrV - Simulations of plasmas and sputtering profiles for coating systems - Methods to produce thin films of refractory metals in small diameter tubes (< 10 mm), including electrochemical means - HIPIMS on SC RF cavities and more - Structured films - Coatings as permeation barriers for high transparency vacuum chambers - flexible (!) insulating coatings - Coating/treating of long (30m) accelerator vacuum systems without dismounting the beamline - Novel cleaning techniques for UHV applications - Simulation of electrochemical processes in complex geometries Technology Department 10 October 2014 S. Calatroni & M. Taborelli 29