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Reaching and Measuring XHV ( ï‚£ 10 -12 Torr)

Reaching and Measuring XHV ( ï‚£ 10 -12 Torr). - Luminosity for accelerators - Lifetime in storage rings. Reaching XHV is commercially easier than measuring it. A CERN modified Helmer gauge did measure 10 -14 Torr XHV is not official - Pressure ï‚£ 10 -7 Torr are still called UHV.

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Reaching and Measuring XHV ( ï‚£ 10 -12 Torr)

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  1. Reaching and Measuring XHV(10-12 Torr) - Luminosity for accelerators - Lifetime in storage rings Reaching XHV is commercially easier than measuring it A CERN modified Helmer gauge did measure 10-14 Torr XHV is not official - Pressure  10-7 Torr are still called UHV F. Le Pimpec

  2. How DID they make light bulb work ? ♦ Since 1800 the electric arc light was known. However, the life time of a filament made of carbon was poor. ♦ The problem was in obtaining a high enough vacuum in the bulb and getting rid of the oxygen in the residual gas Use of the first Evaporable Getters Bulb Installed in 1901 at the Livermore’s (CA)Fire station. C filament - 4 W Phosphorus pumped lamp tend to have a red cast F. Le Pimpec

  3. Why Measure Total Pressure ? Extractor Partial Pressure gives information on the contents of the vacuum Total pressure can be computed from the partial P measurements Operational in the same range (UHV) The use of hot and cold gauge style device need calibration for every single species for accurate readings – chemistry sensitivity RGA’s electronics are sensitive to the beam passage ! And are still not cheap compared to gauges ! RGA F. Le Pimpec

  4. UHV - XHV Total Pressure • Xray limitation due to the e- hitting the grid : Ions are desorbed from the Collector. Remedies : Modulation • ESD from the gauges elements – Reducing emission current : WrongThe grid will pump then release molecules • Installing a hot gauge in a small tube – Transpiration effectDespite a higher pressure thegauge will read lower. Solution: nude gauges – but sensitivity to stray ions from surroundings Modify Extractor gauge with hidden collector (U. Magdeburg) F. Le Pimpec

  5. Ref. “Le Normand CERN vacuum note” Ref. “Sorption of Nitrogen by Titanium Films,” Harra and Hayward, Proc. Int. Symp. On Residual Gases in Electron Tubes, 1967 1cm2 Ti vs Other Getters in Accelerator Ba - Ca - Mg : High vapor pressure. Trouble if bake out is requested Zr - Nb - Ta : Evaporation temperature too high Typical sublimation rate 0.1 to 0.5 g/hr 0.5 g/hr ; MTi =48g/mol 0.5/(48*3600) = 2.9 10-6 mol.s-1 1ML~1015 atom.cm-2 2.9 10-6 mol.s-1. Avogadro = 1.74 1018 atom.s-1 1 ms is necessary to evaporate 1 ML 3 minutes = 180E3 ms hence ML for 1cm2 A) Pumping Speed calculated at RT B) Wide variations due to film roughness C) For H2, competition between desorption and diffusion inside the deposited layers F. Le Pimpec

  6. Also True for Thin Films TiZr and TiZrV V. Baglin et al. F. Le Pimpec

  7. Ionodesorption by heavy energetic ions on technical surfaces 1.5 109 Pb53+ ions (per shot) under 89.2° grazing incidence and 4.2 MeV/u E. Mahner et al. F. Le Pimpec

  8. Ion-desorption on Al surfaces F. Le Pimpec (*) 300°C in the measurement of M.H. Achard

  9. fast head-tail instability NLC Fast Head tail - straight M. Pivi Electron Cloud F. Le Pimpec

  10. COII - N - 2R • COIIIL • InjBELL1 • Inj BEIR1 • E3L • RFS2R TiN/Substrate & Electron Cloud Roughness is an issue F. Le Pimpec

  11. TiZrV coating TiZrV coating 2 h at 300C, CO injected at NEG T=60C Hilleret et al. Getter & Electron Cloud Low SEY : Choice for the NEG of the activation T and t . Conditioning (photons e-ions) Contamination by gas exposure, or by the vacuum residual gas, increases the SEY; even after conditioning. Angles of incidence, of the PE, change the shape of the curve at higher energy F. Le Pimpec

  12. TiN/Substrate & Electron Cloud NLC: 130 eV e-beam conditioning TiN/SS  =0.5 Roughness is an issue ≤ 10-9 Torr Vacuum Recontamination TiN/Al F. Le Pimpec

  13. Oxidized Cu disk Al disk with triangular shape Alternative solution :Playing with Roughness Very rough surfaces emits less SE, because SE can be intercepted by surrounding “walls” F. Le Pimpec

  14. Oxidized Cu disk Al disk with triangular shape Alternative solution :Playing with Roughness Simulation Reality F. Le Pimpec

  15. Al disk with triangular shape Alternative solution :Playing with Roughness Simulation Reality F. Le Pimpec

  16. Dynamic UHV – NEG solution In accelerator Cu, Al or SS are the technical materials of choice, high conductivity • Cu and SS, can be baked at high temperature, Al cannot (200°C)  special design, or ways, to activate a NEG pumping solution • SS and NEG coating have a lower conductivity compared to Cu or Al, wakefield issues  skin depth & vacuum chamber size determination • A leak during an activation might lead to scrapping the chamber (2m of Be chamber, vertex detector, for LHC 106 CHF) • Cycles of venting/activation need to be assessed for the lifetime of the machine F. Le Pimpec

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