The International Linear Collider (ILC) is at R&D stage requires first estimates of possible solutions for challenging vacuum requirements. ASTeC vacuum science group is involved in studies for three subsystems of ILC.
The positron source uses a helical undulator to generate polarised photons of ~10 MeV at the first harmonic. Unlike many undulators used in synchrotron radiation sources, the ILC helical undulator vacuum chamber will be bombarded by photons, generated by undulator, with energies mostly below the 1st harmonic. Achieving the vacuum specification, of ~100 nTorr, in a narrow chamber, of 4 to 6 mm, with a large length, of 100 – 200 m, makes the design of the vacuum system challenging. Possible vacuum system design solutions were studied for two cases: cryogenic and room temperature
Damping rings are important subsystems of the ILC. Our aim is to find the optimum approach to the vacuum system technology in order to achieve the required vacuum levels with reasonable conditioning time. It turns out that the optimum vacuum design uses a NEG coated tubular vacuum chamber. In this case, since almost all inner surface of vacuum chamber will be NEG coated, the gas density along the beam does not depend on the choice of material for a vacuum chamber. The choice of vacuum chamber material between stainless steel, aluminium and copper is then driven by beam impedance, thermal conductivity requirement and cost.
Vacuum design for the ILC beam delivery system should also meet very high vacuum requirement under intensive SR irradiation with MeV range photon energy.
This paper describes the vacuum specifications, calculations of the flux and energy of photons irradiating the undulator vacuum chamber and considers possible vacuum system design solutions.
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