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Update of the vacuum system for the CLIC two-beam modules

Update of the vacuum system for the CLIC two-beam modules. C. Garion CERN/TE/VSC. LCWS, 23-26 September 2011. Outline. Vacuum system in the CLIC module requirements Specificities Vacuum dynamics for a non-baked system Technological solutions for the vacuum system in the CLIC module

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Update of the vacuum system for the CLIC two-beam modules

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  1. Update of the vacuum system for the CLIC two-beam modules C. Garion CERN/TE/VSC LCWS, 23-26 September 2011

  2. Outline • Vacuum system in the CLIC module • requirements • Specificities • Vacuum dynamics for a non-baked system • Technological solutions for the vacuum system in the CLIC module • Vacuum tests of two solutions • Comparison of the technologies • Few words on dynamic vacuum • Conclusion

  3. Vacuum system in the CLIC module Requirements • Field ionization studies resulted in a lowering of the vacuum threshold for fast ion beam instability to: pressure < 1 nTorr [G. Rumulo] • Non heating of the RF systems to guaranty the high precision assembly • Vibration free vacuum system for the quad stabilization Specificities • Non-baked system  vacuum is driven by water • Low conductance (beam pipe diameter ~ 10 mm) and large areas (~5000 cm2/AS) 6 Courtesy of D. Gudkov Internal volume of an accelerating structure Typical shape and dimensions of an accelerating structure disk

  4. Vacuum dynamics for a non-baked system Elements of theory Non baked system: Main molecular specie is water sticking probability and sojourn time are not negligible (whereas for a baked system the time of flight is the most important parameter) Activation energy of desorption 10-13 s Temperature Usually, vacuum technical surfaces exhibits a wide range of binding energy (distribution density). Sticking probability depends also the sticking factor and also on the coverage. Courtesy of M. Taborelli

  5. Vacuum dynamics for a non-baked system Elements of theory For the design of a vacuum system the outgassing rate is usually used. For an non baked system, a simplified evolution law is used: D. Edwards Jr. Journal of Vacuum Science and Tech.,14(1977)606 From an engineering point of view: q [mbar.l/s/cm2] ~ 2.10-9 / t[h] (valid for all metals)

  6. Technological solutions for the vacuum pumping system in the CLIC module External pumps on a central tank Courtesy of A. Samoshkin

  7. Vacuum tank Compact pumps Technological solutions for the vacuum pumping system in the CLIC module Small NEG pump connected to main RF components Tank Support Courtesy of D. Gudkov

  8. Vacuum tests and simulations of the vacuum system in the CLIC module Dedicated accelerating structure Heat transfer equation: Gas flow equation (1D): Vacuum model

  9. Vacuum tests and simulations of the vacuum system in the CLIC module Solution 1: Test set-up Penning Gauge Turbomolecular pump Insulation valve Pirani Gauge Vacuum manifolds (25*28, 30*30 mm2) Cap with Indium sealing Penning Gauge

  10. Vacuum tests and simulations of the vacuum system in the CLIC module Solution 1: Test results Pressure profile along beam axis after 100h of pumping Evolution of pressure •  Good agreement between the measurements and the simulation • Non significant influence of manifold size • 7.10-9 mbar is reached after 100 hours of pumping Pressure field after 100h of pumping

  11. Vacuum tests and simulations of the vacuum system in the CLIC module Solution 2: Test set-up Penning Gauge Insulation valve NEG cartridge Ion pump Nextorr pump from SAES Vacuum manifold Turbomolecular pump Compact NEG and ion pump

  12. Vacuum tests and simulations of the vacuum system in the CLIC module Solution 2: Test results Pressure field after 100h of pumping Evolution of pressure • Good agreement between the measurements and the simulation • 3.10-9 mbar is reached after 100 hours of pumping

  13. Extension of the vacuum model to the CLIC module Pressure profile for the main beam Vacuum model of the module (Not up to date version ) for the solution 1 Pressure profile for the drive beam Static pressure field

  14. Technological solutions for the vacuum pumping system in the CLIC module Next steps • Full vacuum model of the module with parameters as close as possible to present baseline • Installation of a Residual Gas Analyzer: • influence of methane and noble gases • Optimization of ion pumps : number and location • Influence of the SiC damping loads: • increase the gas load • reduce the vacuum conductance • Influence of compact loads • Influence of venting duration, venting gas

  15. Technological solutions for the vacuum pumping system in the CLIC module Comparison of the two solutions

  16. Dynamic vacuum in the accelerating structures S. Calatroni et al. • Different vacuum inside the PETS and the accelerating structures can be considered: • Static: pressure after pump down without RF power and beams • Dynamic: during breakdown • Dynamic: during RF pulses without breakdown

  17. Assumptions: 1012 H2 molecules released during a breakdown [Calatroni et al.] Gas is at room temperature (conservative) Requirement: Pressure<10-9mbar 20ms after breakdown Monte Carlo simulation or thermal analogy Dynamic vacuum in the accelerating structures Maximum pressure during time Longitudinal distribution as a function of time Vacuum degradation remains localized close to the breakdown and seems not to be an issue.

  18. Vacuum in the accelerating structures with RF Principle: Field emission leading to electron stimulated desorption and/or to local heating • Estimation of dynamic pressure: • Dark current simulations from SLAC • ESD data on unbaked copper at high e- energy from CERN [Pasquino, Calatroni] • Introduce these into MC models and get gas distribution, with reasonable assumptions on molecule’s speed Direct measurement: feasibility study on going [K. Osterberg]

  19. Vacuum in the accelerating structures with RF Influence of Dose on ESD Conditioning after ~1014 e-/cm2 Decrease of desorption yield with 1/dose0.5 Study on the influence of the heat treatment on going

  20. Vacuum in the accelerating structures with RF Influence of e- energy on ESD 54_SSH104C • Increase up to 8 keV, then constant (or even small decrease) • Study on the influence of the heat treatment on going

  21. Conclusions Test set-up and vacuum models have been developed to study the static vacuum in the CLIC two beam module. A good agreement between the measurements and the estimations is achieved. Two technological solutions have been (and are being) tested. The solution based on NEG cartridge combined with a small ion pump is promising. Dynamic vacuum study is on going.

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