M. Gilchriese

ATLAS UpgradeMechanics/Cooling and System Design

by LBL

January 2008

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Motivation

• Pixels– Material reduction, particularly for B-layer => improvement in light

quark rejection(for given b-tagging efficiency), although how much is physics dependent.

• Strips– Increased integration ie. staves(or equivalent in forward direction)

– Material reduction would be nice, but not the principal motivation

• Pixels and Strips– Improved system design – more system engineering up front

– What does that mean?• Integrated design of electrical and optical services(power, signals) and

cooling(plumbing) to lead to lower material and better reliability

• Weakest area of current ATLAS ID(particularly the plumbing…)

• Requires substantial(and continuous) engineering and technical support, well coordinated

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Pixels

• Two areas of activity so far– Layouts for B-layer replacement alternatives that can be generalized to SLHC

in the barrel region – see Maurice’s talk– Development of concepts using low-density, thermally conducting carbon foam.

• Why foam?– Perhaps applicable to both “monolithic” structures and staves. Note that “stave”

here also means equivalent for disks(pie sectors similar to ones we made for current pixel system).

– My original idea was to see if carbon nanotubes(CBNT)(that have very high thermal conductivity along their length) could be joined into foam….but quickly found out this seems to be difficult…but then

– Fortuitous coincidence of ongoing development of low density, modest thermally conductive foam for different applications (radiators for space craft and for military aircraft) in company with whom I worked on current pixels…interested in development of their concept and also of CBNT foam

– Not really explored much previously. Why? Carbon foams with good thermal conductivity have existed for years but dense(typically 0.5 g/cc or so) and expensive

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Very Early Concepts• Foam• Cooling tube(glued to foam)• Surface for mounting modules• Structural support from carbon

fiber “skins” glued to foam

88mm

37.5mm

24.4mm

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Low Density, Thermally Conducting Foam

• The development underway starts with Reticulated Vitreous Carbon (RVC) foam that has a density of about 0.06 g/cc and a thermal conductivity of about 0.07 W/m-K

• Through a proprietary chemical vapor deposition (CVD) process, oriented, highly conducting carbon is deposited on the RVC ligaments by Allcomp, Inc.

• This greatly enhances the thermal conductivity(goal is about factor of 600) and improves the strength

• Very roughly we think the thermal conductivity K is related to the density by

K ~ (1000-1200) x ( - 0.06)/(2.2 x “wiggle factor”)

or about 30+/-10, maybe.

• Insufficient data so far to verify this simplistic formula

• Note if CBNT could be made into foam……

K ~ 1400 x /(2.2 x “wiggle factor”)

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Pixel Stave Prototype Development

• Thermally conducting foam obtained from Allcomp, Inc– 0.18 g/cc as delivered

– Thermal conductivity not measured (yet)

• Small prototype (20 cm long and about 2.4 cm wide) made – see photos on next pages– Small aluminum tube(2.9mm OD and 2.3mm ID) used to simulate

about what might be used for CO2 at SLHC

– Foam machined (easy) to shape and with groove for tube

– CGL7018 used to couple tube to foam

– Hysol 9396 loaded with Boron Nitride (30% by weight) used to couple facings to foam

• One facing is YSH70 cloth, 140 microns thick

• Second facing is K13D2U 4-ly laminate 300 microns thick (90-0-0-90 orientation)

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Pixel Stave Prototype - II

Tube with CGL7018

YSH-70 and K13D2U glued to foam

Tube in foam with CGL7018

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Pixel Stave Prototype - III

• Final assembly(foam+fiber halves glued together around tube)

• 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

X0 of C is 42.7 g/cm2

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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 heaters to about match Power/Area

Label Emis BG Ave SD Max Min UnitA1 0.95 19.0 27.41 0.65 28.4 25.9 CA2 0.95 19.0 27.36 0.80 28.4 23.8 C

T in boxes

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Results

0

2

4

6

8

10

12

14

16

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

Note if CO2 used as coolantthen reference temperature could be about -30C. Thusdelta T of 10 => T of -20C.

FE

-I4

goal

FE

-I3

norm

al

Max

. sp

ecIncludes sensors & power conv. But not cables.

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Nominal Design – Short Strips

Bus cable

Hybrids Coolant tube structure

Carbon honeycomb or foam

Carbon fiberfacing

Readout IC’s

10cm detectors, each with 4 rows of chips on hybrids

Hybrids glued to detectors and this assembly glued to mechanical/cooling support

~ 1 meter

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What Has Been Done• Prototypes fabricated and studied

– 1m long for mounting silicon modules(see talk by Haber)– Three thermal prototypes, each about 1/3m long, with heaters, silicon, cables, dummy

hybrids to simulate nominal design• Three different tube types(to simulate compatibility with C3F8, C2F6/C3F8 mixtures and CO2)• Varied facing thickness and adhesives• Thermal measurements(IR imaging) before and after thermal cycling from 20C <-> -35C fifty times

completed• Measured weights as input to material calculations

– Preliminary demonstration of removal/replacement of silicon on stave completed.

• Design studies and FEA– Primarily of nominal design(hybrids glued top of silicon, short strips)

• Thermal performance and thermal runaway• Gravitational deflections and support concepts• Thermal distortion (as detector is cooled down)• Long strips ie. outer barrels.

– But also some work on • Bridged hybrid

• Other – hermeticity, endcaps, production, R&D plan, risks………..• Summary only here – see Backup slides and references therein

From presentation for ValenciaUpgrade R&D meeting in Dec.

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Prototype Construction

1m prototype

2.8mm tube/foam

4.9 mm tube/foam

Flattened tube

Note prototype width is about 7cm – set in 2006

POCO foam: about 0.5 g/cc thermally conducting carbon foam

Facings are K13D2U fiber laminates

Carbon honeycomb

All tubes aluminum

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Thermal Prototypes

Water at about 20C

IR images

Before andafter thermal cycling between20C and -35C50 times

Bus cableAluminahybrids

Heaters 0.3mm silicon

Label Emis BG Ave SD Max Min Unit A1 0.95 19.0 24.76 0.67 26.4 23.6 C A2 0.95 19.0 24.86 0.71 26.4 23.5 C A3 0.95 19.0 24.15 0.69 26.3 22.9 C A4 0.95 19.0 24.81 0.75 26.4 23.5 C A5 0.95 19.0 24.49 0.67 26.1 23.4 C

Label Emis BG Ave SD Max Min Unit A1 0.95 19.0 20.63 0.12 20.9 20.4 C A2 0.95 19.0 20.57 0.12 20.9 20.4 C

3.3 W/hybrid(0.55 W/chip)

No Power

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Major Prototype Lessons• Thermal performance - T between coolant and dummy detector

– Same after thermal cycling to -35C fifty times. No evidence of lost coupling of tube to facing.

– Same within measurement error for facing thickness in range about 0.25 – 0.7 mm. This also validated by FEA calculation.

– Same within about 15% for all three tube types, also expected from FEA. Better for round tube with foam.

T measured agrees with T FEA to within about 1.5C or better, so can have some confidence in FEA

• Deflection measurements (of 1m prototype) agree with calculations within about 15%.

• Multiple successful trials of gluing dummy silicon to bus cable with SE4445(thermally conducting, flexible adhesive used to attach current pixel modules), removal using simple tooling(essentially a guided wire), clean up and reattach at same spot.

• See Backup for the details

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Thermal Performance

-30

-25

-20

-15

-10

-5

0

5

10

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

Tube Wall Temperature(C)

Max

Det

ecto

r T

emp

erat

ure

(C)

0.25 W/chip, 1mW/mm2

0.5W/chip, 1 mW/mm2

0.125 W/chip, 1mW/mm2

0.25 W/chip, 2mW/mm2

0.25 W/chip, 0 mW/mm2

C3F8

CO2

C2F6/C3F8

Note in this design, chiptemperatures are within<2C of detector temperature

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Thermal Model – Bridged Hybrid

Wire bonds, simulated as thin solid, reduced K to 97/mK

Chips 0.38mm thick (148W/mK)

Al Cooling tube 0.21mm ID

Separation between facings 4.95mm

10cm

Foam bridge support

1mm air gap for bridge

Calculations underway

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Interface to Barrel Support

• Have looked quickly at different support options

• Current preference is for shell-like overall support with support points about every 50 cm.

• More on this topic in the engineering session.

• Note that this implies strong coupling of stave design with shell eg. where is the stiffness and not just the obvious support interfaces.

Light weight composite sandwich rings

Locating pins in rings

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System Design

• Requires engineers (and more physicists) to be serious

• LBL engineers still almost completely occupied by finishing pixel installation at CERN

• Some work done on B-layer replacement constraints and concepts

• And some early work on basic layout assumptions

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Outlook - 2008

• Pixels– Finite element calculations of thermal performance to compare with

prototype measurements => infer K of foam from this and use to estimate performance of different layouts. Compare K with direct measurements

– Allcomp has submitted SBIR proposal to DoE to develop foam for our applications(and theirs) and perhaps later CBNT foam

– Have many more ideas than technical manpower or funds to follow

• Strips– Complete calculations on bridged hybrid– Respond to review committee. – Outcome of review(April perhaps) will help determine future direction

• System Design– Very limited availability of LBL engineering….pixel completion, lack

of funds for system design and competition from other (NSD) projects

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Long Term Outlook

• Our large role in the current pixel project in the area of mechanics/cooling and system (services) implementation has been equal to the best within ATLAS.

• Options for the SLHC – in principle (neglecting funding and personnel constraints)1. Similar broad role for both pixels and strips. I believe this is only an

option to consider if ATLAS as a whole forms a tightly integrated design team that covers both. Not yet clear if this will happen. It should.

2. Broad role in pixels, building on our experience3. Narrow role in pixels or strips eg. stave design and fabrication4. No role

• Options 1 or 2 likely require a decision by us within about the next year (do we want to try). Option 3 later (~ 2010).