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LEP and LHC double walled tubes experiences

LEP and LHC double walled tubes experiences. Sergio Calatroni. LEP couplers. Double walled tube – coupler extension – “chemise”. LEP Coupler “crisis” – circa 1994. Many people took part to the coupler study at that time Problem: deconditioning

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LEP and LHC double walled tubes experiences

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  1. LEP and LHCdouble walled tubes experiences Sergio Calatroni

  2. LEP couplers Sergio Calatroni - 16.3.2010

  3. Double walled tube – coupler extension – “chemise” Sergio Calatroni - 16.3.2010

  4. LEP Coupler “crisis” – circa 1994 • Many people took part to the coupler study at that time • Problem: deconditioning • Traced back to desorption and re-adsorption of gases onto cold surfaces • Outgassing + multipacting: solutions • Ti coating of all parts • Fixed coupler • Change impedance from 50 Ohm to 75 Ohm • Smooth surfaces with less outgassing • Bake the ceramic • DC bias • Clean room procedures • Factual review by R. Losito CERN-SL-2002-057 ECT Sergio Calatroni - 16.3.2010

  5. Double walled tubes: fabrication • 316 LN stainless steel, forged blanks • Integral machining by turning • Advantages: • Lower Electron Stimulated Desorption • Smoothness – surface quality • Manufacturing cost in a series comparable to standard metalworking (F. Bertinelli) Sergio Calatroni - 16.3.2010

  6. Copper coating • Copper sputter coating preferred over electroplating • Advantages: • Lower outgassing • Lower Electron Stimulated Desorption (ESD) • Better Thermal Desorption Spectrometry (TDS) • Satisfactory RRR • Problem: • Difficult adhesion of copper on stainless steel • (C. Benvenuti et al. CERN LEP2 Note 94-21) Sergio Calatroni - 16.3.2010

  7. ESD measurements (500 eV e- after 200°C / 24h bakeout) Rolled+welded and Cu sputter coated Full machining and Cu sputter coated Sergio Calatroni - 16.3.2010

  8. Copper ESD measurements Cu sputter coated Cu electroplated Sergio Calatroni - 16.3.2010

  9. Copper TDS measurements Cu sputter coated Cu electroplated Sergio Calatroni - 16.3.2010

  10. RRR measurements Sergio Calatroni - 16.3.2010

  11. Thickness at 700 MHz: effect of RRR RRR 10 RRR 1 Sergio Calatroni - 16.3.2010

  12. Copper thickness: room temperature, 700 MHz Ideal thickness = 4 m Sergio Calatroni - 16.3.2010

  13. Copper coating by sputtering Adhesion of Cu on s.steel is poor because it does not bind to CrO Idea: Ti underlayer, followed by Cu coating without breaking the vacuum. Metal-metal adhesion generally very good Sergio Calatroni - 16.3.2010

  14. Problem: BN • Stainless steel is vacuum fired at 950 °C • 316 LN steel contains some boron to increase hot workability (a few ppm) • If B > 9 ppm (MnS precipitates could act as possible nucleation sites) it may segregate at the surface as BN, with thickness of several nm (S. Sgobba, EST/SM/MB 00-11-25) • BN is hexagonal, called sometimes “white graphite”, hydrophobic • Cannot be removed by detergents • Film can peel-off S. Sgobba M. Taborelli Sergio Calatroni - 16.3.2010

  15. Solution: BN • Vacuum fire at 950 °C • Electropolish the surface (removes BN and becomes mirror like) • Second vacuum firing at 950 °C to remove H2 introduced by electropolishing • Careful to use slow temperature ramp to avoid deformation of double wall Sergio Calatroni - 16.3.2010

  16. LHC couplers • 260 (?) new LEP double wall tubes, very successful operation • LHC were made following LEP recipes • Total: 25 pieces (?) Sergio Calatroni - 16.3.2010

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