Integrated Stave Mechanics/Cooling Backup

1. Integrated StaveMechanics/CoolingBackup ATLAS Upgrade Workshop Valencia December 2007 M. Cepeda, S. Dardin, M. Gilchriese, C. Haber and R. Post LBNL W.Miller and W. Miller iTi

2. Introduction • We collect here some backup information for the presentation on integrated stave mechanics/cooling. • A few notes • Work on the integrated stave began in the Fall of 2006 • The dimensions of prototypes, and a number of FEA calculations, were set then when detectors were assumed to be about 6cm in width. • Thus prototypes were built assuming about 6 cm wide detector dimensions rather than the current 10cm “baseline”. Thus a principal goal of the “6 cm” prototypes is to validate FEA estimates of the thermal performance, and then use the FEA to calculate for 10 cm • In addition, the properties assumed for materials, particularly for thermal FEA calculations have evolved somewhat with time as have assumptions for detector power after irradiation. • Link to information on integrated stave mechanics/cooling http://phyweb.lbl.gov/atlaswiki/index.php?title=ATLAS_Upgrade_RandD_-_Mechanical_Studies

3. Prototypes

4. Reminder of Prototype Concept Link to drawings is here • For prototypes……..fixed > 1 year ago • K13D2U, high-modulus facings • Adjust facing thickness(layers) to achieve stiffness desired • Carbon-fiber honeycomb in-between facing, fixed thickness • Three types of tubes • Flattened(C3F8) • Big round with POCO foam(C3F8/C2F6) • Small round with POCO foam(CO2) 71.5mm POCO foam: about 0.5 g/cc thermally conducting carbon foam

5. Prototype Stave Core Assembly

6. Weight and Material • Measured weights for 1m prototype(10 ply facings) and extrapolation to thinner facings(3 ply) and width for 10cm detectors given below. Note assumes minimal side closeouts • Tube is flattened. Would get similar numbers for POCO foam+smaller tube

7. Thermal Measurements • Measurements before and after thermal cycle 50 times to -35C are summarized below • Delta T calculated from average of inlet+outlet water T for convenience. Max and min given to nearest 0.5C. Delta T rounded to nearest degree. • No difference between before and after thermal cycle within errors • Note tube(4.8) with foam compared to flattened is better as is smaller tube with foam. We attribute this to better coupling to tube • FEA results are given(for fixed fluid temperature everywhere). Agreement within 20% or roughly 1.5C. Writeup of FEA is at link here

8. Remove/Replace • We have completed a number of trials of gluing glass and silicon with SE4445 adhesive that was used to attach all pixel modules to local supports in the current pixel detector. Has decent thermal properties and already tested to 50 MRad for pixels. • Attach, let cure(both week long and about 2 month long tested), remove, clean and replace. • Straightforward mechanically, only need simple tooling for close-together detectors – promising (no surprise since did this already for pixels) • Pictures on next pages, although hard to see

9. Glass slide after removal(slide at bottom of picture) Starting to peel SE4445 Silicon detector after removal and before cleanup After about 2 month cure. Done with two detectors, same result Removal Pictures

10. Thermal FEA

11. Comments • Some of the most recent results are included here • Many previous studies with somewhat different parameters. • See the wiki http://phyweb.lbl.gov/atlaswiki/index.php?title=ATLAS_Upgrade_RandD_-_Mechanical_Studies

12. Thermal Runaway in 10cm Module • Thermal Runaway Issue: Based on new detector heating curve- (revised by Nobu-MIWG meeting November 2007) • Quarter section from 10cm wide stave, single U-Tube • Spacing of U-Tube divides heat load collected by each symmetrically • Chip heat load and surface heating treated as variables

13. Thermal Runaway Model Parameters

14. Surface Heating Curve New curve based on 1mW/mm2 at 0ºC (Nobu-MIWG Nov. 2007) and exponential temperature dependence

15. Thermal Runaway Solutions Plot of peak detector temperature leading up to runaway (as function of tube surface wall temperature) Surface heating 1mW/mm2 @ 0C Exponential temperature dependency (Nobu-MIWG Mtg. Nov. 2007)

16. Thermal Runaway-Variable Surface Heating Comparing effect of surface heating using 0.25W/chip as baseline SurfaceHeating 1mW/mm2 0 2mW/mm2

17. Detector Surface Heating Curve at right shows slight deviation of solution convergence Deviation caused by using peak silicon nodal temperature whereas solution is based on the detector outer surface edge average

18. Thermal Runaway-Typical Thermal Plot Chip: 0.5W Coolant Tube Surface -16.8ºC Peak chip: 6.18ºC Peak detector edge: 5.17ºC Throughout solutions peak chip and peak detector differential temperature stays near 1.0 to 1.1ºC With 0.25W/chip the temp difference is nominally 0.5ºC Nearly thermal runaway point

19. Bridge Thermal Model • Salient Features • High conductivity (700W/mK, 0.5mm thick) CC bridge material support for 0.28mm thick hybrid(1W/mK) • 40 chips @ 0.25W/chip • Detector 0.28mm thick, 148W/mK • Allcomp carbon foam for bridge support (isotropic 45W/mK) • Carbon Foam for tube support (45/45/45 W/mK) • Reduced density over POCO foam (0.2g/cc versus 0.5 g/cc) • Sandwich foam • Allcomp foam option, ~0.1g/cc @ 3W/mK • Comparison with Hybrid on 10cm Detector • Thermal solution with both with inner tube wall at -28ºC • Simulates -30ºC with 8000W/m2K • No change made to material properties in 10cm detector with integrated hybrid

20. 10cm Detector-No Bridge • Material Properties • See previous slide (#2) • 40 chips per detector, 80 total • 0.25W/chip Q (Si)=0W • Tube inner surface -28ºC, no convection coefficient • Interest in ΔT from chip and detector surface to tube surface • Peak chip temperature • Middle hybrid region: -20.5ºC • Peak Detector • Middle hybrid region: -21.5ºC • ΔT in region of max gradient: 6.5ºC

21. 10 CM Wide Stave-No Bridge • Solution • Replaced honeycomb core with Allcomp carbon foam (<0.2g/cm3: 45W/mK) • Also, replaced POCO foam tube support with same foam • Peak Chip Temp: -22.7ºC • Peak Detector: -24ºC • ΔT (referenced to tube wall) • 4ºC

22. 10 CM Wide Stave-No Bridge • Solution: Simulate “outer” long strip detector • One upper and power hybrid for 10cm detector • 20 chips @ 0.25W/chip • Coolant tube inner surface: -28ºC • Materials, see slide (#2) • Detector • Peak temp beneath hybrid: -24.8ºC • ΔT in region of max gradient: 3.2ºC • Chip Peak Temp: -24.1ºC

23. Thermal Bridge Model (1/2 of 10cm) 1mm air gap for bridge 10cm Wire bonds, simulated as thin solid, reduced K to 97W/mK Al Cooling tube 0.21mm ID Chips 0.38mm thick (148W/mK) Separation between facings 4.95mm Foam bridge support

24. Bridge Thermal Model Enclosed bridge model in an air box. Air participates only through pure conduction. Air fills all cavities not occupied by a solid Air box

25. Model Parameters Cable and adjacent adhesive layers modeled as single layer 0.227mm and K=0.31W/mK

26. Solution with -30ºC Tube 8000 W/m2K 0.5W/chip Q (Si)=0 Slight asymmetry caused by variance in interior coolant wall temperature Chip peak=-16.5ºC Detector max=-21.4ºC

27. Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q (Si)=0 Slight asymmetry caused by variance in interior coolant wall temperature Chip peak=-23.3ºC Detector max=-25.8ºC

28. Solution with -30ºC Tube 8000 W/m2K 0.25W/chip Q (Si)=0 Sandwich foam core 3W/mK, density ~0.06 g/cm3 Bridge foam and tube foam 45W/mk, density ~0.2 g/cm3 (no POCO foam) Peak chip=-21.8ºC Peak detector temp -24.2ºC Wire bonds 97W/mK

29. Fluid Calculations • C3F8 calculations are here for flattened tube and here for round tube • CO2 calculations are here and here. • Summary from main talk reproduced below • Note T(film) is an average around the loop • T(loop) follows from the P vs T curves for the fluids and is rounded to the nearest 0.5C • These calculations are complex and need validation by measurements

30. Adhesive Joint Considerations • There are numerous analytic solutions for adhesive joint shear stress caused by thermal expansion of dissimilar materials • General theme is that the shear stress is a maximum at the ends of joint, and essentially zero at the center • Maximum shear stress at the end is independent of the length of the joint • Key factors are: • modulus of elasticity, CTE, and thickness of joined materials • thickness and shear modulus of the adhesive • Temperature differential • A useful reference to bound the problem: Thermal Stresses in Bonded Joints, W.T. Chen and C.W. Nelson • Suggests for carbon foam joined to aluminum tube with CGL7018 (very compliant adhesive) or EG7658 (semi-rigid) that shear stresses remain within material limits for a 100C temperature change • Prototype testing will confirm our expectations

31. Carbon Foam to Aluminum Tube Joint • 100C temperature differential • Cure temp to -25C • Foam thickness=8mm, G=690MPa, α=4ppm/C • Aluminum wall thickness 0.305mm, E=10Msi, α=12ppmC • Adhesive thickness=0.10mm, Compliant G=40MPa (5862psi), Rigid G=1 GPa • Max shear stress, τ=1062psi, compliantτ= 42psi

32. Computer-Based Solutions • Structural Problems • NASTRAN FE solver • Recent solutions with NE NASTRAN with FEMAP interface • Prior work with MSC NASTRAN, but MSC no longer can bundle the NASTRAN solver with FEMAP pre-processor • Choose not to use PATRAN pre-processor • Fluid/Thermal Problems • Use CFDesign computational fluids dynamics code • Very versatile • Allows use of shell elements for describing interface resistances • HEP Silicon-Based Tracking Detectors • Issue with very, very thin solids mixed in with larger solids • In reasonable sized geometry, some solids may have only surface nodes, and no internal nodes; • possible consequence is reduction of solution accuracy