Update on Pixel Prototype Mechanics/Cooling Structures at LBNL

1. Update on Pixel Prototype Mechanics/Cooling Structures at LBNL February 1, 2008 M. Cepeda, S. Dardin, M. Garcia-Sciveres, M. Gilchriese and R. Post LBNL W. Miller and W. Miller iTi

2. What Are We Doing? • R&D on module supports using low-density, thermally conducting carbon foam + carbon fiber structures • Goal is to investigate both stave-like(or sector-like) structures and monolithic ie. half-shell(or half-disk) structures • Build and test prototypes and do FEA to compare to measurements and predict performance. • Note all barrel concepts assume active edge modules!! Flat surfaces.. • Today • Update of thermal measurements on stave structure • Comparison of these measurements to FEA • Monolithic structure mockup made • Next steps and conclusions

3. Foam • Currently working with foam made by proprietary chemical-vapor-deposition (CVD) process using reticulated vitreous carbon (RVC) foam as a precursor • The RVC has density ~ 0.05 g/cc and is poor thermal conductor with a K ~ 0.07 W/m-K • The CVD-deposited carbon coats the ligaments in the RVC foam, has a very high K and thus raises the effective K by factor ~ 100 but the density only by factor 2-4. • Note this foam (and RVC foam) is straightforward to machine, including moderately complex shapes and has reasonable mechanical properties eg. CTE similar to silicon • So far we have worked with samples (free) of density 0.18 g/cc • Made simple rectangular prototype – foam with tube in middle – to test concept

4. Pixel Stave Prototype - I Foam with groove for tube. Three pieces joined. One side K13D2U laminate 300 microns thick YSH-70 cloth 140 microns thick Foam with groove for tube. Three pieces joined. One side

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

6. Pixel Stave Prototype - III • Final assembly(foam+fiber halves glued together around tube) • Tube is sized for CO2 coolant ie. about 2.2mm ID • Platinum-on-silicon heater in middle to simulate pixel module and copper-kapton heaters on either side to minimize end effects. 260mg/cm2 (exc. Pipe) 24 mm => 130mg/cm2 for Foam 6.9 mm Tube is 2.8mm OD

7. 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 T in boxes Label Emis BG Ave SD Max Min Unit A1 0.95 19.0 27.41 0.65 28.4 25.9 C A2 0.95 19.0 27.36 0.80 28.4 23.8 C

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

9. FEA of Prototype • Single-module in length, corresponding to silicon heater • Heat from both sides • Neglect kapton heaters on either side of silicon heater • Instead have measured effect of additional heaters on the prototype • Figure at right and summarized on next page

10. FEA Comparison • Measured T for about 0.65W/cm2 on both sides of stave is about 14.5C for either sided(very small difference between side with YSH-70 and K13D2U). • Correction for kapton heaters is about -1C. So value to compare with FEA is about 13.5C • FEA predicts 11-15C, taking into account errors in K and thickness of materials – see below. Biggest unknown is foam K.

11. Improvements? • We were conservative in the amount of foam (2mm) between the facing and tube. Subsequent machining trials show that we can reduce this to 0.5-1mm. Reducing to 1mm would reduce the T by 1.5-2C (from calculation). • The facing on the module side is there to (a) provide a surface to mount the module and (b) possibly for stiffness. • We realized that at least (a) can be met with glue alone and this would also likely improve T • See samples with good surface quality that consist of Hysol 9396 + 30% boron-nitride(for thermal conductivity) about 125 microns thick. No facing on front side. See pictures next page. • Would tune thickness and shape of backside carbon-fiber facing to provide required stiffness, if this technique were used.

12. Glue Surface Samples

13. Monolithic Concepts for B-Layer Carbon fiber shell glued to foam • Single half-barrel structure • Modules inside • Drawings show concepts for CO2 cooling, but would just use bigger pipe for CnFm cooling • Concept is simple • Conducting foam • Aluminum tube glued into foam • Tune carbon-fiber outer shell to minimize material but meet stiffness and other mechanical requirements • End-rings (not shown) for additional stiffness(glued to shell) and for inevitable cable and pipe strain relief Round aluminum tube Faces for module mounting Carbon high K foam

14. Monolithic Mockup • We have built a mockup of a monolithic foam-fiber structure(for SLHC B-layer with CO2 cooling) to understand how to do this. • Used low-density RVC foam(not conducting foam) for convenience • See next page for some pictures of details • As built, about 1.7 g/cm for half-barrel(foam, tubes, adhesives, shell) => maybe 4 g/cm for real foam, real shell? Eg. 320 gm + end rings for 80 cm half-barrel • Can easily see how to make mechanical/cooling structure to meet thermal/mechanical requirements. • But mount and remove modules and connections? Needs considerable study – this is the hard part of this design

15. Monolithic Construction

16. Monolithic Options to Study • Will do quick FEA look at alternative monolithic option proposed by Maurice • One-module long model shown here. • Mounting and connection access easier in this concept • What K needed for foam to make this work with fewer tubes per module? • Could keep one-tube per module, however • Note in this case likely to need carbon fiber facings both sides for overall stiffness.

17. Next Steps and Conclusions • Foam • Measure thermal conductivity. Commercial firm, laser diffusivity • Anyone else interested and capable to test by other means? Have samples... • Have submitted proposal to develop foam and characterize it with company but wont know for a few months if approved. • Module removal trials on samples with glue surface + foam. Is this a problem? If yes, go back to thin laminate on surface, works for both stave and monolithic • Stave/sector • Proof-of-concept complete…..could proceed to real design with existing materials. Note this would also work for disk sectors. Important to have unified concept for barrel and disks, in my opinion • Would like to test with CO2 if we can find someone interested with this capability…. • Monolithic structure • Simple analysis of design variants to be done. What can work. • Would clearly work as is for flat half-disks….don’t have to worry about module mounting issues • Need basic structural analysis(sag, stability…) to size carbon fiber aspects. • But possible another step would be to model overall layout for both barrel and disks based on foam/fiber concept, mixing monolithic and stave approaches eg. B-layer and monolithic disks, remainder of barrel layers based on staves • Would welcome collaboration with interested groups

18. Backup • Weight of monolithic mockup, roughly, without end rings • RVC foam+adhesives: 6.1 gms • Tubes: 3.6 gms • Shell: 3 gms • This gives only about 1.7 gm/cm per half-shell length • Extrapolate to higher density foam • Foam x 3 or about 18 gms • Tubes same • Shell. Don’t know guess at least x 2 or 6 gms • About 4 gm/cm of half-shell length or roughly 320 gm for 80 cm length, not including end rings • Of course, really need full structural analysis….