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Eliana La Francesca Dottorato in fisica degli acceleratori (XXXI ciclo )

Material science and accelerator R&D: Reflectivity and Photo Yield measurements of vacuum chamber technical surfaces. Eliana La Francesca Dottorato in fisica degli acceleratori (XXXI ciclo ). Relatore interno : prof. M. Migliorati Relatore esterno : dott . R. Cimino. Outline.

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Eliana La Francesca Dottorato in fisica degli acceleratori (XXXI ciclo )

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  1. Material science and accelerator R&D: Reflectivity and Photo Yield measurements of vacuum chamber technical surfaces Eliana La Francesca Dottorato in fisicadegliacceleratori (XXXI ciclo) Relatoreinterno: prof. M. Migliorati Relatoreesterno: dott. R. Cimino

  2. Outline • Synchrotron radiation detrimental effects • Reflectivity and Photo Yield • BessyII measurements • Conclusions and Future work 2 Roma, 16 October 2017 Eliana La Francesca

  3. Synchrotron Radiation detrimental effects • Photon stimulated desorption • Heat load on the accelerator walls • Production of photo emitted electrons (e- cloud effect) Beam instability 3 Roma, 16 October 2017 Eliana La Francesca

  4. Synchrotron Radiation interaction with Matter Reflected + Absorbed + Transmitted Specular reflected Scattered 4 Roma, 16 October 2017 Eliana La Francesca

  5. Synchrotron Radiation interaction with Matter Reflected + Absorbed + Transmitted Photo-electrons generation Heat Load Electron cloud effect 5 Roma, 16 October 2017 Eliana La Francesca

  6. SR and electron cloud generation Photo-emitted electrons can be: • produced directly by SR (dipoles): emitted in the orbit plane (not participate to electron cloud build up). • Produced by the reflected or scattered light (dipoles and free field zone): emitted perpendicularly to the orbit plane (generate secondary electrons) Beam instability Original representation F. Ruggero 6 Roma, 16 October 2017 Eliana La Francesca

  7. Synchrotron Radiation interaction with Matter Reflected + Absorbed + Transmitted Photo-electrons generation Heat Load Electron cloud effect 7 Roma, 16 October 2017 Eliana La Francesca

  8. FCC Parameters http://tlep.web.cern.ch/content/fcc-hh Version 1.0 (2014-02-11) Parameters LHC H-L LHC FCC-hh Dipoles at 1.9 K Total Power to dissipate such HL at cold bore temperature: 3 GW 4 Roma, 16 October 2017 Eliana La Francesca

  9. Synchrotron Radiation interaction with Matter Arc SR Heat Load = 28.4 (44.3) W/m/aperture Reflected + Absorbed + Transmitted To be increased in high temperature parts (absorbers) To be increased in cold parts (Superconductive Magnets) 9 R. Cimino, V. Baglin and F. Schäfers, PRL. 115 (2015) 264804 Roma, 16 October 2017 Eliana La Francesca

  10. Reflectivity X-Ray Reflectivity depends on a limited number of parameters: • Photon energy and light polarization • Angle of incidence • Surface roughness • Material 10 Roma, 16 October 2017 Eliana La Francesca

  11. Specular Reflectivity VS Incidence angle Cu 11 http://henke.lbl.gov/optical_constants/ Roma, 16 October 2017 Eliana La Francesca

  12. Reflectivity X-Ray Reflectivity depends on a limited number of parameters: • Photon energy and light polarization • Angle of incidence • Surface roughness • Material 12 Roma, 16 October 2017 Eliana La Francesca

  13. Specular Reflectivity VS Roughness FCC-hh SR incidence angle: 0.035 deg (0.62 mrad) REFLEC simulations 13 Roma, 16 October 2017 Eliana La Francesca

  14. Reflectivity X-Ray Reflectivity depends on a limited number of parameters: • Photon energy and light polarization • Angle of incidence • Surface roughness • Material 14 Roma, 16 October 2017 Eliana La Francesca

  15. Specular Reflectivity VS Material FCC-hh SR incidence angle: 0.035 deg (0.62 mrad) 15 REFLEC simulations Roma, 16 October 2017 Eliana La Francesca

  16. Specular Reflectivity: the case of Carbon REFLEC simulations FCC-hh SR incidence angle: 0.035 deg (0.62 mrad) Attenuation depth (): P(x)=exp(-x/) For x=the intensity of X-rays falls to 1/e of its value at the surface. R. Cimino, V. Baglin and F. Schäfers, PRL. 115 (2015) 264804 20 nm of C can reflect all photons (C) 3.5 nm (X-ray range) 15 Roma, 16 October 2017 Eliana La Francesca

  17. BESSY-II Optic Beamline and Reflectometer 17 A.A.Sokolov,etal,Proc.of SPIE92060J-1-13(2014) Roma, 16 October 2017 Eliana La Francesca

  18. BESSY-II Optic Beamline and Reflectometer • Incidence angle θ: -90° – 90° • Detector in-plane 2θ: -180° – 180° • Detector off-planeχ: -4° – 4° • Sample – detector: 310 mm • Sixaxes sample positioning • Sample currentmeasurement • GaAsP-Photodiodes • Detector slits, pinholes 18 A.A.Sokolov,etal,Proc.of SPIE92060J-1-13(2014) Roma, 16 October 2017 Eliana La Francesca

  19. Bessy II Measurements PhotoYield: PY= Ne/N • Photon Energy range 351800 eV • Beam height h=0.3 mm • Incident Beam measurement • GaAsP Photodiodes (4x4mm2) (1.2*4mm2) • Incidence angle 0.25, 0.5, 1 deg • Reflectivity measurement Specular Reflectivity Scattered Light Detector Total Specular Mirror 19 Roma, 16 October 2017 Eliana La Francesca

  20. Copper samples AFM (20x20µm2) Cu 1A Polished 78.4 nm Cu 1A Cu 2A 18 Side A – means polished Side B – means lapped Roma, 16 October 2017 Eliana La Francesca

  21. Copper sample Cu1A and REFLEC simulations At grazing incidence angle contaminants are influencing Cu Reflectivity 21 Roma, 16 October 2017 Eliana La Francesca

  22. Copper sample Cu1A and REFLEC simulations C K edge REFLEC BESSY II O K edge Cu L2,3 edge REFLEC At grazing incidence angle contaminants are influencing Cu Reflectivity 22 Roma, 16 October 2017 Eliana La Francesca

  23. Specular Reflectivity VS Photon Energy Cu 1A Carbon coating reduces reflectivity at low energy O K edge Cu L2,3 edge C K edge Cu 1A + CC At high energy reflectivity is significantly enhanced 20 23 Roma, 16 October 2017 Eliana La Francesca

  24. Photo Yield VS Photon Energy Cu 1A Peaks correspond to absorption edge Cu L2,3 edge C K edge Cu 1A + CC O K edge Carbon coating reduces Photo Yield at high energy 20 24 Roma, 16 October 2017 Eliana La Francesca

  25. Reflectivity VS Photon Energy Cu 1A Low energy photons can be reflected even at high incidence angles 25 Roma, 16 October 2017 Eliana La Francesca

  26. Total Reflectivity VS Specular Reflectivity Spec. Reflectivity Ra= 10 nm Cu 1A specular reflection Ra=0.5 nm = 5 deg 100 10-1 10-2 10-3 10-4 10-5 10-6 small angle scatter wide angle scatter hn=1500 eV Reflectivity 5 10 15 twotheta (deg) 26 Roma, 16 October 2017 Eliana La Francesca

  27. Total Reflectivity VS Specular Reflectivity Ra= 27 nm Cu 2A specular reflection Ra=0.5 nm = 5 deg 100 10-1 10-2 10-3 10-4 10-5 10-6 small angle scatter wide angle scatter hn=1500 eV Reflectivity 27 5 10 15 twotheta (deg) Roma, 16 October 2017 Eliana La Francesca

  28. Angular distribution of Reflectivity (in plane) Cu 1A hn=1500 eV Cu data (full line) Cu + CC data (dashed line) Cu 2A hn=1500eV 28 Roma, 16 October 2017 Eliana La Francesca

  29. Angular distribution of Reflectivity (off plane) hn=1500 eV qi=0.25 deg Cu 1A Cu 2A Roma, 16 October 2017 Eliana La Francesca

  30. Photo Yield VS Incidence angle hn= 1800 eV Tech. Surf PY= Ne/N • Preliminary Results: • little dependence on roughness • Carbon coating seems to reduce PY 30 Roma, 16 October 2017 Eliana La Francesca

  31. Conclusions and Future work • At grazing incidence angle contaminants deeply influence Reflectivity. • For technical surfaces scattered light cannot be neglected. • Photo Yield does not seem to significantly depend on roughness. • Carbon coating seems to increase Total Reflectivity and reduce absorption and related Heat Load. • In the next year we plan to continue the measurements and analysis on different technical materials. 31 Roma, 16 October 2017 Eliana La Francesca

  32. Thank you for your attention. Roma, 16 October 2017 Eliana La Francesca

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