# Presentation: 704283

## SLHC Pixel Local Supports Based on Thermally Conducting Carbon Foam

- E. Anderssen, M. Cepeda, S. Dardin, M. Garcia-Sciveres, M. Gilchriese, N. Hartman and R. Post
- LBNL
- W. Miller and W. Miller
- iTi
- Henry Lubatti, Gordon Watts, Tianchi Zhao, Dept. of Physics
- Colin Daly, Bill Kuykendall, Dept. of Mech. Engr.
- University of Washington
- May 29, 2008
- CERN

## Outline

- Concepts
- Examples of implementation
- Prototype fabrication and tests
- Foam materials testing
- Mechanical and thermal modeling
- Foam development plans
- Design optimization plans
- Prototype fabrication plans
- Conclusions

## Concept Overview

- Thermally conducting, low-density carbon foam as
- Structural material and simultaneously
- For conduction of heat to cooling tube(s)
- Same concept for barrel and disk local supports
- Implementation can differ for inner barrel elements, outer barrel elements and disks but keep basic concept same

- Foam

## Outer Layers - Example

- “Large” area planar sensors. Conservative module design (similar to current)

- ...

- 34.8

- 26.8

- Module on back

- 986mm

- 38.4

- CARBON FOAM

## Inner Layers - Examples

- Monolithic structures
- R  4 cm only
- Modules one side
- Modules alternate sides
- Single-sided staves
- R  4 cm
- R  10 cm
- Single-chip modules(e.g. 3D)

## Disks

- Layout with radial and  overlap in progress – not trivial
- Modules on both sides of structure as now
- Radial overlap requires offset in Z

- Back modules

- Front modules

- Module offset
- in Z

## 1st Pixel Prototype “Stave”

- VG

- 1st Pixel Prototype “Stave”

- Tube with CGL7018

- YSH-70 and K13D2U glued to foam

- Tube in foam with CGL7018

- Allcomp 1 foam

## LBNL Thermal Test Set-Up

- VG

## Thermal Results

- T does not depend strongly on facing  thickness
- Note double - side heat not 2 x single – side heating

## FEA Model

- VG

- Heater heat loads, 8.38W
- Silicon heater, 148 W/mK, 0.28mm thick
- Silicon heater adhesive, SE4445, 0.6 W/mK, 0.004in thick, two places
- YSH70 open cloth fabric, one layer, 0.6 W/mK, 0.14mm
- YSH70 adhesive, 1.55 W/mK, 0.002in
*Foam properties varied, from 6 to 30 W/mK*
- Al cooling tube, 180 W/mK, 2.8mm OD and 2.19mm ID
- Water, convective film coefficient, 66,000 W/m2K, 1.0L/min
- Set 20.25oC on inner tube wall
- K13D2U facing, 1 W/mK, 0.28mm thick
- K13D2U adhesive, 1.55 W/mK, 0.002in thick

## FEA Thermal Solutions

- Double heater

- Single heater

- Agrees with direct measurement of foam(K  = 5.8)  within understanding of component K values

## Additional Prototypes

- Identical width, thickness and adhesives to older prototype (Allcomp 1) but shorter in length (7.4 cm).
- YSH-70 facings on both sides.
- Heater only on one side. Compare at 0.63 W/cm2
- IR and water flow same as older prototoype ( 1.0 l/min)

## Thermal Results

| Foam | (g/cc) | K(W/m-K) | Tave/W |
| --- | --- | --- | --- |
| Allcomp 1 | 0.18 | ~ 6
We measured | ~ 1.2 |
| Allcomp 2 | 0.21 | Not known | ~ 1.0 |
| POCO | 0.09 | ~ 17(z)
~ 6(x-y)
Vendor supplied | ~ 1.3 |
| Koppers | 0.21 | ~ 30(z?)
Vendor supplied | ~ 1.0 |

- B-layer and L1 – recent cooling tests

- First results quite encouraging
- Work with companies to up K and keep  low
- SBIR with Allcomp just starting
- Koppers making samples with goal of 
- POCO already there at sample basis but fragile

- Note that production batch e.g. Koppers
- is 150,000 – 200,000 cm3. An outer stave
- is 125-250 cm3 (depends on coolant, width)

- Present detector
- -10C power off

- Single-sided W

## Foam Materials Testing

- Done at U. of Washington
- Preliminary results
- Additional tests with bonded facings to be done at U. Washington and Allcomp
- Practical note – Allcomp foam easier to handle, machine

| Foam | (g/cc) | E(ksi) | G(ksi) |  | Comments |
| --- | --- | --- | --- | --- | --- |
| Allcomp 1 | 0.18 | 15 | 6 | 0.27 | Low? |
| Allcomp 2 | 0.21 | 150 | 53 | 0.43 |  |
| POCO | 0.09 | 4-8 | - | - | Sample too small |
| Kfoam | 0.21 | 40 | 17 | 0.17 |  |

## Thermal Modeling

- Structure models – fix tube wall T
- Thermal runaway – just started
- Example of outer stave concept
- T depends on foam K

## Thermal Runaway

- Estimates of sensor heating (too simple, must be updated)
- Part of optimization....see later

| T in C | Pixel@16 cm | Pixel@21 cm | Pixel@1e16 |
| --- | --- | --- | --- |
| -35 | 0.003 | 0.002 | 0.017 |
| -30 | 0.006 | 0.004 | 0.033 |
| -25 | 0.011 | 0.008 | 0.061 |
| -20 | 0.020 | 0.015 | 0.113 |
| -15 | 0.036 | 0.026 | 0.203 |
| -10 | 0.064 | 0.046 | 0.356 |
| -5 | 0.110 | 0.080 | 0.614 |
| 0 | 0.187 | 0.135 | 1.037 |

- W/cm2 vs temperature
- Assumes 280 micron fully depleted silicon operating at 600V....too simplistic
- Note 3D sensors @100V more
- like “16 cm” column

- Foam K=6 W/mK

## More Thermal 

- Outer stave
- Variations – see plot
- Note that these results also apply to single-chip wide stave
- Needs detailed optimization
- Monolithic designs
- Not as well studied
- Depends on number of tubes
- For one tube per module about same as stave
- For fewer....need colder

**0.6 W/cm****2 **** Differential from sensor to coolant wall is 10.6 ̊C**

## “Disk” Model

- _Single_ tube per 4-chip module – interest in differences, will do 2 tubes later
- Issue is addition of step of foam

- Flex circuit

- Flex circuit

- Sensor

- Sensor

- Chips

- Chips

- Foam

- Foam

- Carbon fiber

- Epoxy

- Kapton cable and glue layers – not present in disk but for comparison with stave

## “Disk” Model Thermal Results

- Remember _**single tube**_
- Tmax (no sensor heating)
- Difference in T for module on step is small  1C or less => foam step is viable option for disks.

- Cable layer removed. Foam has k = 6 W/mK. Peak temperature is 21.5 C above the coolant.
- 

| Facing |  | Foam |  |
| --- | --- | --- | --- |
| In-plane K | Transverse K | K | T |
|  |  | 6 | 21 |
|  |  | 10 | 16 |
|  |  | 15 |  |
| 600 | 20 | 6 | 17 |
| 600 | 20 | 10 |  |
| 600 | 20 | 15 |  |

## Mechanical Analysis Examples

- Gravity sag <5 microns

- Thermal distortion < 10 microns

- Gravity sag < few microns for rigid 5-point support

- Thermal distortion  50 microns

- All very preliminary. Needs much more work along with support structure design

## Foam Development

- Note that Allcomp foam is different than graphite foams from POCO or Koppers
- POCO and Koppers interested, Koppers making low density samples for us to test
- Allcomp foam uses RVC (reticulated vitreous carbon) foam as base and adds high thermal conductivity material to ligaments in the RVC foam
- Allcomp has just received special funding to develop foam for HEP application
- Make and test samples of different density, porosity, heat treatment, etc
- Make stave-like test structures and measure mechanical & thermal performance

- Allcomp foam

- 3in by 6in by 2in thickness block
- 100 ppi and 0.12 g/cc

## Design Optimization

- In the next few months we want to explore quickly a wide range of design options based on foam concept
- Meet thermal requirements(based on sensor heating update to appear soon). Calculate thermal runaway (obviously depends on coolant assumed)
- Some mechanical input(for material estimates)
- _Minimize material_
- Span many (all?) options
- Tube types – Aluminum, carbon fiber, stainless, CuNi – and number of tubes per module(1 every 2 cm width or can we do better..)
- Facing materials – none (just glue), fiber, carbon-carbon, TPG, diamond
- Foam combinations
- All one density and K
- Mix low density and higher density
- Overall design optimum(or optima) for different regions(inner, outer, disk)

## Prototype Fabrication

- Follows design optimization
- Also depends on choice of coolant and when choice is made
- Coolant path
- Choice of coolant is critical
- Prototype “stave” sent to CPPM for tests
- Hope to establish CO2 capability in US relatively soon
- Continue to make very small prototypes for foam characterization
- Number and type of small prototypes depends on design optimization studies – what makes sense
- Ambitious goal would be to build full-length prototype outer stave by early 2009 based on design and small prototype studies.

## Conclusion

- Local supports based on thermally conducting carbon foam continues to look like good idea
- Two immediate next steps
- Design optimization, for which a critical assumption is coolant type
- Continue and expand foam development
- Very small and small prototype development (limited mostly by resources)
- Goal would be to build full-length outer stave prototype for thermal and mechanical tests by early 2009. Combine with electrical?
- Note – have ignored implications of B-layer replacement pending Task Force Report.