1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR1 Endcap Requirements Brief overview of SCT Endcap Requirements layout, X0, thermal, positioning, stability CF Structures tendering Future plans, K5/KB comments Summary

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR2 Inner Detector Overview

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR3 Disc Layout

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR4 Basic Requirements Support ~1000 modules + services on 9 discs Correct place, stable ~168 kg per Endcap, 7.5 kg per disc Safe under normal loads gravity, cooldown, moisture, N2 pressure… Safe during transport, assembly 4-hit coverage (with Barrel SCT) to  = 2.5 (9 deg) Self-calibrating with tracks (module overlaps) and FSI Minimise 3-hit gaps Spread hits evenly in radius Haywood, ATL-INDET Fit in SCT Endcap envelope TB , ATL-IS-ER-0017 (J. Tarrant)

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR5 Radiation Minimise X0 Optimise p T resolution Minimise conversions etc. for calorimeters Yardstick is Silicon wafer/module material Spread material evenly Talk from Tim Jones Survive 10 years operation Up to 100 kGrey ionising dose Up to 2 x /cm 2 /a 1-MeV equiv. Neutron flux

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR6 Thermal Remove power of ~1000 modules 7.5 W Hybrid, 240 microW/mm 2 (max) irradiated Si Use C3F8 evaporative cooling Si at ~ -7 deg C Minimise radiation damage Avoid thermal runaway Care with convective heat loads on top modules Endcap thermally neutral: ~-7/+25 degC in/outside Outer thermal enclosure and wings active Inner bore cools down; Pixels thermally neutral Active shield unnecessary during normal running Heater still needed during maintenance to prevent condensation Dry nitrogen purge Avoid condensation on coldest pipes (allow for ~-25 degC)

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR7 Positioning Wafers ordered; position fixed Overlaps in r and  for hermiticity and alignment High/low modules in a ring Respect tolerances, allow for HV Disc edges protect modules Care with tolerances to not overlap edges

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR8 Physics requirements for Module Positioning “Do as well as reasonably possible” Tracking can use software alignment Trigger can use LUT now Relaxes requirements since TDR Discussed in ATL-IS-ER-0027 Main constraint is overlap for track-alignment 67, 100, 290 micron for inner/middle/outer Also mounts of module need care Avoid deforming modules out-of-plane 100 micron disc flatness (machined), 50 micron module mounts

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR9 Stability Vibrations Maximise fundamental frequencies and damping Keep amplitude well below resolution: << 20 micron in-plane; more tolerance in z. Slower movements Endcap as a whole Can follow well with tracks and align to Pixels/TRT 250 micron per day ok Internal distortions Minimise; 50 micron in-plane on a disc OK? Use FSI and tracks to follow Modules on a disc: 12 micron in r  in a day TDR, from Snow/Weidberg ATL-INDET Allow for 2 degC change. Moisture effects very slow.

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR10 Requirements Highlights Stability: Challenging but important Radiation length: Minimise Positioning: Relatively easy to achieve

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR11 Comments on Disc Order Discs supplied by industry Major expense, main lead-time Order is for plane disc 2 skins on a core and 2 rings, no machining, no holes Largely independent of services and layout Details such as inserts can be changed later (K5/KB) But thickness, ring-depth (r) may change Procede as far and fast as possible for K5 assumption

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR12 K5/KB Implications If K5: full-speed ahead Incorporate comments from FDR Finalise tender docs, design, finance January 2002 PRR (Assume K5) Tender If KB: We have time to take maximum advantage Thickness, ring dimensions Lot of work Though in principle, KB fits with current disc design Manpower and money spent…(at least NIKHEF) Likely Delay to programme Need care to check all will work

1st Nov 2001 Nigel Hessey SCT Endcap Structures FDR13 Summary Main FDR emphasis: Disc, Cylinder, and Wing: CF Support Structure Major expense items and lead times Thermal Shields Does the design meet the requirements Also: Cylinder Services Layout Disc services: May change K4 layout = Existence proof of a solution Avoid lengthy K5/KB discussion