Towards Fabrication of a Mechanical Prototype Stave

1. Towards Fabrication of a Mechanical Prototype Stave

2. Assumption • Good idea to build a mechanical prototype stave that would allow evaluation of the mechanical and thermal properties of the stave concept • Note this was done extensively for similar pixel structures • In addition to actual design, need some decisions and some studies to set some of the design specifications

3. Allowable Sag – What Is It? • Current ATLAS structures are very stiff • Out of plane deviations are measured module by module eg in case of pixels to better than 10 microns. Pixel phi resolution is about 10 microns. Expect to include out of plane deviations module-by-module in track reconstruction. • Obviously the effect of out-of-plane(sag or bow) scales with intrinsic resolution eg for 80 microns have to know deviations to roughly 80 microns, although this depends in detail on the layout. • Can we predict sag of staves in large structure this well? • Or increase stiffness such that sag is small enough that prediction is accurate enough? • Or go to in-situ monitored situation(ala muons, IR lasers like CMS, more complicated FSI….) • Defining the allowable sag is a critical parameter to bound before proceeding with a prototype

4. Cooling Practicalities • Bill’s calculations suggest that bulk coolant temperatures((about -25C) from the existing evaporative C3F8 are cold enough. • ATLAS has invested or will invest considerable resources into evaporative cooling and we will have much experience by time upgrades relevant. It’s going to be hard to throw this away without convincing need. • Evaporative system piping/fittings are currently almost all metallic. This was deemed necessary from concerns about C3F8 interactions with plastics and fault conditions concerns. • The exceptions know to me in the pixel system are • PEEK seals to provide electrical isolation. These have gone through more than 2 years of testing, including irradiated parts held at pressure in warm C3F8 for two years. • Epoxy attachment of fittings will be required for repair of pixel barrel tubes and for capillary fabrication. This is being qualified now, because of pixel corrosion problem. • Fault conditions in the evaporative system may result in 13-14 bar in local structures. Current requirement is that local structures either withstand this or if they fail, do not damage neighbors. • Decisions • Evaporative is the baseline? • Same fault tolerance? • If so, all metallic system or do we allow plastics and adhesives?

5. Prototype Stave Length • Is 2m practical to build – yes • And survey - clearly possible but requires significant infrastructure • Significant effort was required to evaluate thermal(and other distortions) for pixel structures that were about 50-80 cm in size. • Do we have capability now (BNL, LBL) to perform appropriate survey or other measurements on a 2m mechanical prototype? • Not obvious to me. Needs evaluation before proceeding. • 1m I believe is (just) within capabilities at LBL