1. M. Gilchriese ATLAS Upgrade Mechanics/Cooling and System Design by LBL January 2008

2. M. Gilchriese 2 Motivation Pixels –Material reduction, particularly for B-layer => improvement in light quark rejection(for given b-tagging efficiency), although how much is physics dependent. Strips –Increased integration ie. staves(or equivalent in forward direction) –Material reduction would be nice, but not the principal motivation Pixels and Strips –Improved system design – more system engineering up front –What does that mean? Integrated design of electrical and optical services(power, signals) and cooling(plumbing) to lead to lower material and better reliability Weakest area of current ATLAS ID(particularly the plumbing…) Requires substantial(and continuous) engineering and technical support, well coordinated

3. M. Gilchriese 3 Pixels Two areas of activity so far –Layouts for B-layer replacement alternatives that can be generalized to SLHC in the barrel region – see Maurice’s talk –Development of concepts using low-density, thermally conducting carbon foam. Why foam? –Perhaps applicable to both “monolithic” structures and staves. Note that “stave” here also means equivalent for disks(pie sectors similar to ones we made for current pixel system). –My original idea was to see if carbon nanotubes(CBNT)(that have very high thermal conductivity along their length) could be joined into foam….but quickly found out this seems to be difficult…but then –Fortuitous coincidence of ongoing development of low density, modest thermally conductive foam for different applications (radiators for space craft and for military aircraft) in company with whom I worked on current pixels…interested in development of their concept and also of CBNT foam –Not really explored much previously. Why? Carbon foams with good thermal conductivity have existed for years but dense(typically 0.5 g/cc or so) and expensive

4. M. Gilchriese 4 Very Early Concepts Foam Cooling tube(glued to foam) Surface for mounting modules Structural support from carbon fiber “skins” glued to foam 88mm 37.5mm 24.4mm

5. M. Gilchriese 5 Low Density, Thermally Conducting Foam The development underway starts with Reticulated Vitreous Carbon (RVC) foam that has a density of about 0.06 g/cc and a thermal conductivity of about 0.07 W/m-K Through a proprietary chemical vapor deposition (CVD) process, oriented, highly conducting carbon is deposited on the RVC ligaments by Allcomp, Inc. This greatly enhances the thermal conductivity(goal is about factor of 600) and improves the strength Very roughly we think the thermal conductivity K is related to the density  by K ~ (1000-1200) x (  - 0.06)/(2.2 x “wiggle factor”) or about 30+/-10, maybe. Insufficient data so far to verify this simplistic formula Note if CBNT could be made into foam…… K ~ 1400 x  /(2.2 x “wiggle factor”)

6. M. Gilchriese 6 Pixel Stave Prototype Development Thermally conducting foam obtained from Allcomp, Inc –0.18 g/cc as delivered –Thermal conductivity not measured (yet) Small prototype (20 cm long and about 2.4 cm wide) made – see photos on next pages –Small aluminum tube(2.9mm OD and 2.3mm ID) used to simulate about what might be used for CO2 at SLHC –Foam machined (easy) to shape and with groove for tube –CGL7018 used to couple tube to foam –Hysol 9396 loaded with Boron Nitride (30% by weight) used to couple facings to foam One facing is YSH70 cloth, 140 microns thick Second facing is K13D2U 4-ly laminate 300 microns thick (90-0-0-90 orientation)

7. M. Gilchriese 7 Pixel Stave Prototype - II Tube with CGL7018 YSH-70 and K13D2U glued to foam Tube in foam with CGL7018

8. M. Gilchriese 8 Pixel Stave Prototype - III Final assembly(foam+fiber halves glued together around tube) Platinum-on-silicon heater in middle to simulate pixel module and copper-kapton heaters on either side to minimize end effects. 6.9 mm 24 mm Foam 260mg/cm 2 (exc. Pipe) => 130mg/cm 2 for X 0 of C is 42.7 g/cm 2

9. M. Gilchriese 9 Thermal Performance IR camera used Water coolant at 1.0 l/min at 20C. Vary power level in silicon heater And separately in copper-kapton heaters to about match Power/Area LabelEmisBGAveSDMaxMinUnit A10.9519.027.410.6528.425.9C A20.9519.027.360.8028.423.8C T in boxes

10. M. Gilchriese 10 Results Note if CO2 used as coolant then reference temperature could be about -30C. Thus delta T of 10 => T of -20C. FE-I4 goal FE-I3 normal Max. spec  Includes sensors & power conv. But not cables.  

11. M. Gilchriese 11 Nominal Design – Short Strips Bus cable Hybrids Coolant tube structure Carbon honeycomb or foam Carbon fiber facing Readout IC’s 10cm detectors, each with 4 rows of chips on hybrids Hybrids glued to detectors and this assembly glued to mechanical/cooling support ~ 1 meter

12. M. Gilchriese 12 What Has Been Done Prototypes fabricated and studied –1m long for mounting silicon modules(see talk by Haber) –Three thermal prototypes, each about 1/3m long, with heaters, silicon, cables, dummy hybrids to simulate nominal design Three different tube types(to simulate compatibility with C3F8, C2F6/C3F8 mixtures and CO2) Varied facing thickness and adhesives Thermal measurements(IR imaging) before and after thermal cycling from 20C -35C fifty times completed Measured weights as input to material calculations –Preliminary demonstration of removal/replacement of silicon on stave completed. Design studies and FEA –Primarily of nominal design(hybrids glued top of silicon, short strips) Thermal performance and thermal runaway Gravitational deflections and support concepts Thermal distortion (as detector is cooled down) Long strips ie. outer barrels. –But also some work on Bridged hybrid Other – hermeticity, endcaps, production, R&D plan, risks……….. Summary only here – see Backup slides and references therein From presentation for Valencia Upgrade R&D meeting in Dec.

13. M. Gilchriese 13 Prototype Construction 1m prototype 2.8mm tube/foam 4.9 mm tube/foam Flattened tube Note prototype width is about 7cm – set in 2006 POCO foam: about 0.5 g/cc thermally conducting carbon foam Facings are K13D2U fiber laminates Carbon honeycomb All tubes aluminum

14. M. Gilchriese 14 Thermal Prototypes Water at about 20C IR images Before and after thermal cycling between 20C and -35C 50 times Bus cable Alumina hybrids Heaters 0.3mm silicon 3.3 W/hybrid(0.55 W/chip) No Power

15. M. Gilchriese 15 Major Prototype Lessons Thermal performance -  T between coolant and dummy detector –Same after thermal cycling to -35C fifty times. No evidence of lost coupling of tube to facing. –Same within measurement error for facing thickness in range about 0.25 – 0.7 mm. This also validated by FEA calculation. –Same within about 15% for all three tube types, also expected from FEA. Better for round tube with foam. –  T measured agrees with  T FEA to within about 1.5C or better, so can have some confidence in FEA Deflection measurements (of 1m prototype) agree with calculations within about 15%. Multiple successful trials of gluing dummy silicon to bus cable with SE4445(thermally conducting, flexible adhesive used to attach current pixel modules), removal using simple tooling(essentially a guided wire), clean up and reattach at same spot. See Backup for the details

16. M. Gilchriese 16 Thermal Performance C3F8 CO2 C2F6/C3F8 Note in this design, chip temperatures are within <2C of detector temperature

17. M. Gilchriese 17 Thermal Model – Bridged Hybrid Wire bonds, simulated as thin solid, reduced K to 97/mK Chips 0.38mm thick (148W/mK) Al Cooling tube 0.21mm ID Separation between facings 4.95mm 10cm Foam bridge support 1mm air gap for bridge Calculations underway

18. M. Gilchriese 18 Interface to Barrel Support Have looked quickly at different support options Current preference is for shell-like overall support with support points about every 50 cm. More on this topic in the engineering session. Note that this implies strong coupling of stave design with shell eg. where is the stiffness and not just the obvious support interfaces. Light weight composite sandwich rings Locating pins in rings

19. M. Gilchriese 19 System Design Requires engineers (and more physicists) to be serious LBL engineers still almost completely occupied by finishing pixel installation at CERN Some work done on B-layer replacement constraints and concepts And some early work on basic layout assumptions

20. M. Gilchriese 20 Outlook - 2008 Pixels –Finite element calculations of thermal performance to compare with prototype measurements => infer K of foam from this and use to estimate performance of different layouts. Compare K with direct measurements –Allcomp has submitted SBIR proposal to DoE to develop foam for our applications(and theirs) and perhaps later CBNT foam –Have many more ideas than technical manpower or funds to follow Strips –Complete calculations on bridged hybrid –Respond to review committee. –Outcome of review(April perhaps) will help determine future direction System Design –Very limited availability of LBL engineering….pixel completion, lack of funds for system design and competition from other (NSD) projects

21. M. Gilchriese 21 Long Term Outlook Our large role in the current pixel project in the area of mechanics/cooling and system (services) implementation has been equal to the best within ATLAS. Options for the SLHC – in principle (neglecting funding and personnel constraints) 1.Similar broad role for both pixels and strips. I believe this is only an option to consider if ATLAS as a whole forms a tightly integrated design team that covers both. Not yet clear if this will happen. It should. 2.Broad role in pixels, building on our experience 3.Narrow role in pixels or strips eg. stave design and fabrication 4.No role Options 1 or 2 likely require a decision by us within about the next year (do we want to try). Option 3 later (~ 2010).