Availability and Failure Effects of NLC Main Linac Mechanical Movers(LCC-0141)

We analyze the probability of failure and the failure effects of the quadrupole and RF girder translation stages (''movers'') in the 500 GeV CM NLC Main Linac. In order to achieve its alignment tolerances, the NLC main linac will require a large installation of remote controlled translation stages with multiple degrees of freedom. In particular, each of the 591 quads in each 250 GeV main linac will be mounted on a magnet mover with 3 degrees of freedom (x, y, roll); each of the 2304 RF structure girders in each linac will be mounted on a girder mover with 5 degrees of freedom (x, y, roll, pitch, yaw). Simulation studies of main linac operation typically assume that all movers are operational at all times, in order to limit the complexity of the simulation. This is obviously not a realistic expectation for a system with so many components, especially when the number of sub-elements of each mover (stepper motors, rotary encoders, position transducers, cabling, control electronics, database, operator) are considered. The unavailability risk of the mover system is of particular concern for the NLC, since very few accelerators have ever been built with such a large fraction of its beamline hardwaremore » on remote-controlled translation stages. In order to predict the availability of the movers, it is necessary to estimate a few quantities, specifically: how often will a mover break (mean time between failures, or MTBF); how long will it take to repair a mover (mean time to repair, or MTTR); what is the performance ''hit'' which accrues when movers are broken? To answer the first two questions we used historical failure data from the two large mover systems at SLAC, in the arcs of the Stanford Linear Collider (SLC) and in the Final Focus Test Beam (FFTB). For the final question, we can get some estimate from simulation studies of the NLC main linac in normal operation.« less