Reliability Simulations for a Linear Collider

A new flexible tool for evaluating accelerator availability was developed as part of the US Linear Collider Technology Options Study. The linear collider designs considered were based on the GLC/NLC X-band and TESLA Superconducting proposals, but modified to meet the US physics requirements. To better model some of the complexities of actual operation, a simulation program was written, which included details such as partial fixes or workarounds, hot-swappable repairs, multiple simulta- neous repairs, cooldown periods before access, staged recovery from an outage, and both opportunistic and scheduled machine development. The main linacs and damping rings were modeled in detail with component counts taken from the designs, and using MTBFs and MTTRs from existing accelerator experience. Other regions were assigned a nominal overall failure rate. Variants such as a single tunnel or conventional positron source were also evaluated, and estimates made of the sensitivity to recovery or repair times. While neither design was predicted to be sufficiently reliable given present experience, the required improvements were estimated to increase the overall project cost by only a few percent.