# Presentation: 620684

## 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

## 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

## 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

## Pixel Stave Prototype - I

- Foam with groove for tube. Three pieces joined. One side

- Foam with groove for tube. Three pieces joined. One side

- YSH-70 cloth 140 microns thick

- K13D2U laminate 300 microns thick

## Pixel Stave Prototype - II

- Tube with CGL7018

- YSH-70 and K13D2U glued to foam

- Tube in foam with CGL7018

## 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.

- 6.9 mm

- 24 mm

- Foam

- 260mg/cm2
**(exc. Pipe)**

- => 130mg/cm2 for

- Tube is 2.8mm OD

## 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

- 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

- T in boxes

## 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.

- 

- 

## 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

## 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.

## 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.

## Glue Surface Samples

## Monolithic Concepts for B-Layer

- 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

- Carbon high K foam

- Faces for module mounting

- Round aluminum tube

- Carbon fiber shell glued to foam

## 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

## Monolithic Construction

## 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.

## 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

## 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....