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Cavity Treatment (BCP, Heat Treatment & HPR)

Cavity Treatment (BCP, Heat Treatment & HPR). Sergio Calatroni with many contributions from: Rama Calaga, Leonel Ferreira, Antonio Mongelluzzo. Outline. Caveat: several personal remarks What do we want to do, and why Cortical layer, defects etc.. H2 degassing Cleanliness

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Cavity Treatment (BCP, Heat Treatment & HPR)

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  1. Cavity Treatment(BCP, Heat Treatment& HPR) Sergio Calatroni with many contributions from: Rama Calaga, Leonel Ferreira, Antonio Mongelluzzo Sergio Calatroni

  2. Outline • Caveat: several personal remarks • What do we want to do, and why • Cortical layer, defects etc.. • H2 degassing • Cleanliness • How we are going to do it • Surface treatments • Vacuum furnace • HPWR • CERN hardware Sergio Calatroni

  3. Surface treatment goals • Removal of defects • Due to welding (irregularities, beads, etc) • Due to machining (EDM oxidation & cracks, machining chips, etc) • Removal of “cortical layer” • Rule of thumb: 5% sheet thickness either side • Obtaining a smooth surface • Allows highest RF performance (suppression of B-field enhancement at steps, etc.) Sergio Calatroni

  4. Options • Buffered Chemical Polishing, Electropolishing, Centrifugal Barrel Polishing • Need to specialize material removal & finishing treatment? No • Efficient and economical treatment is more important than ultimate performance • My conclusion: BCP Sergio Calatroni

  5. Is it feasible? 4 rods RF dipole ¼ wave All three designs have features which allow correct acid flow and evacuation Sergio Calatroni

  6. BCP Niowave CERN BCP 1:1:2 done 8/2012! 150 µm removed All hardware ready for BCP (but we need to invest for “production”) Sergio Calatroni

  7. Degassing goal • Removal of hydrogen in solid solution • Prevent “hydrogen disease” B. Bonin SRF1991 (DESY) http://accelconf.web.cern.ch/AccelConf/SRF91/papers/srf91d01.pdf M Hakovirta SRF2001 (Tsukuba) http://accelconf.web.cern.ch/accelconf/srf01/papers/pr023.pdf (S. Isagawa J. Appl. Phys. 51 (1980), 4460) Sergio Calatroni

  8. H2 degassing • Done at >600 °C for >24h • H2 partial pressure / furnace total pressure have a peak then have to decrease • Final equilibrium is reached (Sievert’s law for exothermic material) • for 1 ppm H:< 10-7 mbar @ 600 °C< 10-6 mbar @ 800 °C • Note: 30000 ppm@ RT @ 10-8 mbar !!!(but slow kineticsfor uptake) Sergio Calatroni

  9. CERN furnace P=3.5x10-7 mbar @ 650 °C P=1x10-7mbar @ RT Venting with Air Sergio Calatroni

  10. Oxygen contamination • It is well known that Nbacts as a GETTER • When “activated”, ie surface oxide is dissolved in the bulk (> 380 °C), its surface is extremely reactive, and impurities steadily diffuse in the bulk • Surface layer gets contaminated • Diffusion progresses in the bulk with time and temperature • Solution: “light” (chemical) polishing, typically around 20 µm • More material removal may increase H2 uptake from the acid bath Sergio Calatroni

  11. Cleanliness • Removal of dust particles • Prevent electron field emission • (Improves Q) Peak of E-field: 4 rods RF dipole ¼ wave (**) (****) (****) Sergio Calatroni

  12. HPWR CERN • Removal of dust particles • HPWR • Line-of-sight access to all high E-field regions Bulk Nb 1.3 GHz cavity, Ep + HPWR @ CERN, circa year 2000 Recently refurbished with new ultrapure H2O production plant & filters, new controls Sergio Calatroni

  13. New HPWR and clean room From Janic Chambrillon Sergio Calatroni

  14. Conclusions • BCP favoured • Minimal sequence: • Heavy BCP • H2 degassing • Light BCP • HPWR • All crab designs compatible with surface treatments • 4-rods seems not optimal for HPWR • At CERN • HPWR and H2 degassing OK • BCP OK, dedicated cabinet needed for series “production” Sergio Calatroni

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