Vacuum in Accelerators – CERN Accelerator School
16-24 May 2006, Silken Park Hotel San Jorge, Platija d'Aro, Spain
Analytical and Numerical Tools for Vacuum Systems
Vacuum Group, Technical Services Division European Synchrotron Radiation Facility – Grenoble (France)
R. Kersevan
kersevan@esrf.fr http://www.esrf.fr/
Program of the course:
1.
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Why do we need to calculate pressure profiles in an accelerator in the first place
Beam lifetime, emittance blow-up, beam-losses, radiation damage, personal safety issues, etc…
2.
How can it be done The old way…
Analytical methods: Diffusion equation, parabolic profiles, etc…
The modern way, using computers
Analytical methods: symbolic solution of differential equations Numerical methods: Finite-Element Method, Montecarlo, commercial codes, etc…
3. 4. 5.
It's all about the conductance… and the gas load! Conclusions References
Analytical and Numerical Tools for Vacuum Systems - R. Kersevan - ESRF, Grenoble - CAS Vacuum School Silken Park Hotel San Jorge - Platija d'Aro, Spain - June 17-23 2006
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1.

Why do we need to calculate pressure profiles in an accelerator in the first place
Fact: Energetic particles, charged or neutral, interact with matter; In particular, inside the vacuum system of an accelerator, they interact with the residual-gas, which may be detrimental to the correct operation of the machine; The degree of sensitivity to the level (total pressure) and quality (gas composition) of the vacuum is a function of the accelerator type; Few examples, to clarify. The vacuum level and quality of…: … lepton colliders (e.g. B-factories) is strongly affected by the synchrotron radiation (SR)-induced outgassing yield of the materials making the chamber and SR absorbers. Most of the outgassed gases are H2 and light carbon-contaning species (CxHy, CO, CO2, plus water). Their interaction regions (IRs) are very sensitive to the radiation background (damage to the electronics inside the detectors); … high-energy hadron colliders (protons and ions) is strongly affected by the secondary electron emission yield (SEY) of the the materials making the chamber (e-cloud effect). The outgassed species can be heavy gases and/or sputtered materials which could lead to beamlosses ( severe damage of vacuum chamber/leak, radiation damage), heating of cryogenic magnets and cavities ( quenching), and so on; … SR light sources: same as lepton colliders, with the addition of the requirement that the bremsstrahlung (BS) level inside the experimental hutches be low enough to let the users in during the operation of the machine; As a general rule: the lower the pressure (locally and globally), the better; Clear mathematical relationship are known for the description of the interaction between charged beams and residual gases: elastic and inelastic scattering, on leptons and hadrons (in most cases on e- and nucleons), and other interactions;

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