M. Gilchriese

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. PostLBNL

W. Miller and W. MilleriTi

Henry Lubatti, Gordon Watts, Tianchi Zhao, Dept. of Physics

Colin Daly, Bill Kuykendall, Dept. of Mech. Engr.

University of Washington

May 29, 2008CERN

M. Gilchriese

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

• Conclusions2

M. Gilchriese

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

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Foam

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

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…

34.8 26.8

Module on back

986mm

38.4

CARBON FOAM

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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)

5 Potential cable location

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Disks• Layout with radial and overlap in progress – not trivial

• Modules on both sides of structure as now

• Radial overlap requires offset in Z

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Back modules

Front modules

Module offsetin Z

M. Gilchriese7 VG VG 77

1st Pixel Prototype “Stave”

Tube with CGL7018

YSH-70 and K13D2U glued to foam

Tube in foam with CGL7018

Allcomp 1 foam

M. Gilchriese8 VG VG 88

LBNL Thermal Test Set-Up

Silicon heater

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Thermal Results

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0

2

4

6

8

10

12

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0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

P/A(W/cm^2)

De

lta

T a

ve

rag

e

YSH-70 only

K13D2U only

YSH-70 sideHeat both

K13D2U sideHeat both

T does not depend strongly on facing thickness

Note double - side heat not 2 x single – side heating

M. Gilchriese10 VG VG 1010

FEA Model• 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

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FEA Thermal Solutions

Double heater Single heater

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

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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)

M. Gilchriese

Thermal Results

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Foam (g/cc) K(W/m-K) Tave/W

Allcomp 1 0.18 ~ 6We 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. Koppersis 150,000 – 200,000 cm3. An outer staveis 125-250 cm3 (depends on coolant, width)

Present detector-10C power off

Single-sided W

M. Gilchriese

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

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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

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Thermal Modeling• Structure models – fix tube wall T

• Thermal runaway – just started

• Example of outer stave concept T depends on foam K

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H=6000W/m2K (CO2)

T(fluid)=-34ºC @ inlet

Detector peak ~ -24.7ºC

Coolant film ΔT=3ºC

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Thermal Runaway

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• Estimates of sensor heating (too simple, must be updated)

• Part of optimization….see later

T in CPixel

@16 cmPixel

@21 cmPixel

@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

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

-40 -35 -30 -25 -20 -15 -10 -5 0

Coolant Tube Inner Wall Temperature-(C)

Pea

k S

enso

r T

emp

erat

ure

-(C

)

no surface heating1.87mW/mm2 @ 0 C10.67mW/mm2 @ 0 C

W/cm2 vs temperatureAssumes 280 micron fully depleted silicon operating at 600V….too simplistic

Note 3D sensors @100V morelike “16 cm” column

Foam K=6 W/mK

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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

170.6 W/cm2 Differential from sensor to coolant wall is 10.6˚C

-35

-30

-25

-20

-15

-10

-5

0

5

10

-35 -30 -25 -20 -15 -10 -5 0Coolant Tube Inner Wall Temperature-(C)

Pe

ak

Se

ns

or

Te

mp

era

ture

-(C

)

baseline foam 6 W/mK

foam=15W/mK

foam=15W/mK, CC=250/25/250

foam=15W/mK, Cable=200W/mK

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“Disk” Model• Single tube per 4-chip module – interest in differences, will do

2 tubes later

• Issue is addition of step of foam

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Flex circuit

Flex circuit

Sensor

SensorChips

Chips

Foam

Foam

Carbon fiber

Epoxy

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

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“Disk” Model Thermal Results

• Remember single tubesingle tube Tmax (no sensor heating)

• Difference in T for module on step is small 1C or less => foam step is viable option for disks.

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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

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Mechanical Analysis Examples

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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

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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

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Allcomp foam

3in by 6in by 2in thickness block100 ppi and 0.12 g/cc

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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 materialMinimize 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)

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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.

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M. Gilchriese

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.

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