Reliability issues for linear colliders

To deliver a high integrated luminosity over several years of operation, a linear collider must not only meet its energy and luminosity performance goals, but also have a very high hardware availability and operating efficiency. The first challenge is the size and complexity of the facility. If the typical reliability of existing High Energy Physics accelerators is simply scaled to the size of a 500 GeV linear collider, the overall system availability will be too low. The final design must incorporate a more rigorous failure analysis as well as built-in overheads and redundancy. An additional challenge is the complexity of the tuning procedures required to preserve a very small beam emittance. These include beam-based alignment of magnets and rf structures, automated trajectory correction, feedback, emittance and luminosity optimization, and more. Another issue is the inherently large power densities in the beams, which can damage any beamline components they intercept. An extensive machine protection system is necessary to inhibit beam in case of a fault and automatically execute a recovery sequence. This paper will present the important issues in the context of the proposed linear collider designs.