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Electron Stimulated Desorption of OFE Copper

Electron Stimulated Desorption of OFE Copper. Chiara Pasquino, Politecnico di Milano. Dynamic Vacuum: an issue for CLIC accelerating structures. Static Vacuum : 10 -9 mbar [ G.Rumolo , C.Garion ] Dynamic Vacuum : CO 2 , H 2 < 10 -9 mbar. Technical Note, EDMS 1095288.

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Electron Stimulated Desorption of OFE Copper

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  1. Electron Stimulated Desorption of OFE Copper Chiara Pasquino, Politecnico di Milano 9th March 2011, RF Structure Meeting

  2. Dynamic Vacuum: an issue for CLIC accelerating structures • Static Vacuum: 10-9 mbar [G.Rumolo, C.Garion] • Dynamic Vacuum: CO2, H2 < 10-9 mbar Technical Note, EDMS 1095288 http://ilcagenda.linearcollider.org 9th March 2011, RF Structure Meeting

  3. Dynamic vacuum sources due to the High Gradient • Breakdowns: during the discharge a gas burst is always detected; • Dark Currents: FE currents that don’t lead to a breakdown impinge on the Copper surface causing the ESD Effect. FAST ION – BEAM INSTABILITIES 9th March 2011, RF Structure Meeting

  4. Dynamic Vacuum studies : Breakdowns • 2*102 H2 or CO molecules released [exp. Data DC “spark test” reported in PRST-AB12, 092001 (2009)]; • Uniform pressure along the structure after ~ 3ms; • Background pressure recovered after 20 ms, no dynamic vacuum problems. • [C.Garion] 9th March 2011, RF Structure Meeting

  5. Dynamic Vacuum studies : ESD e- are uniformly distributed inside the cell e- on faraday cup e- on faraday cup • Faraday Cup measurement - T18_VG24_Disk_2 – KEK [T. Higo] • ESD measurement on unbaked Copper [ N. Hilleret, CAS Vacuum School 2006 - G. Vorlaufer CERN-Thesis (2002)] NEW ESD EXPERIMENTAL DATA ON UNBAKED OFE COPPER AT HIGH ELECTRON ENERGY NEEDED! • H2 PP = 1.12E-8 mbar 10 times higher • CO2 PP = 3.37E-9 mbar 3 times higher S. Calatroni 9th March 2011, RF Structure Meeting

  6. Dynamic Vacuum studies: theoretical models Gortel Fully Quantum Mechanical Model e- e- Antoniewicz MGR Model 9th March 2011, RF Structure Meeting

  7. Desorption Yield Steady State Condition 9th March 2011, RF Structure Meeting

  8. Sample Campaign • 3 Cleaning Procedures : w/o etching, passivation & SLAC etching • Several Thermal Treatment : Vacuum, Argon, H2 atmosphere @ 1040 or 820 °C 9th March 2011, RF Structure Meeting

  9. H2 Diffusion Profiles :SLAC bonding H2 H2 • Cu – H is an endothermic system! • equal Cs at both surfaces 9th March 2011, RF Structure Meeting

  10. H2 Diffusion Profiles: SLAC bonding THE ANNEALING TIME CAN BE DECREASED !!! 9th March 2011, RF Structure Meeting

  11. ESD Experimental Set-Up 9th March 2011, RF Structure Meeting

  12. ESD Experimental Set-Up 35 KV V 2-3 A A +15 V V A 9th March 2011, RF Structure Meeting

  13. Measurement Scheme • ~ 20 s of desorption pulse; • precise check of the background pressure; • train of measurement continuous check of the pressure through the dual gauge read by Labview [thanks Rocio!!]; • steady state condition useful experimental data. 9th March 2011, RF Structure Meeting

  14. Experimental Data @ 10 KeV: Cu spare samples 9th March 2011, RF Structure Meeting

  15. Experimental Data @ 10 KeV: 19_PCV082C Experimental Error Analysis 9th March 2011, RF Structure Meeting

  16. Energy Correlation: Stopping Powers 9th March 2011, RF Structure Meeting

  17. Energy Correlation: Experimental Data • Increase up to 2.5 KeV, then a small decrease; • From 5 to 15 KeV, no dependence! • Something to be studied in the future! 9th March 2011, RF Structure Meeting

  18. Conclusions • A new experimental set – up has been built in order to provide ESD experimental data for unbaked copper at higher electron energy, as required; • The experimental set – up has been improved and it’s correctly working; • Further investigations about SLAC procedure are needed; • Further investigations on the energy correlation are required as well. 9th March 2011, RF Structure Meeting

  19. THANKS FOR THE ATTENTION!!!! Many thanks to: Sergio, Mauro, Walter, Rocio, Helga, Jan, Markus, Ivo, Donat, Pawel, Luigi, Paul, Wil, Holger!!! 9th March 2011, RF Structure Meeting

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