M. Gilchriese

Integrated StaveMechanics and Cooling

ATLAS Upgrade WorkshopDecember 2007

M. Cepeda, S. Dardin, M. Gilchriese, C. Haber and R. PostLBNL

W.Miller and W. MilleriTi

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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

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Prototypes

• We chose to build three prototypes to approximately simulate tube sizes that would be applicable to C3F8, C2F6/C3F8 and CO2. To answer the question - is this design compatible with all these?

• Tube diameters chosen from practical concerns(ie we had tube or could easily get it) but also from calculations of fluid properties that are summarized in the table below.

Based on 240W, 1 meter length (2 m cooling tube). See Backup for references to more details.

Fluid Tube OD (mm)

Tube ID (mm)

Hydraulic Diameter (mm)

ΔP (mbar)

Coolant (ºC)

ΔT(film) (ºC)

ΔT(loop) (ºC)

C3F8 4.9 4.29 4.29 333 -25 3.5 5 C3F8 4.9(oval) n/a 5.27 121 -25 3.5 2 CO2 2.8 2.19 2.19 638 -35 2.0 1.5

ΔT(film) is drop from “bulk” to wall. ΔT(loop) follows from ΔP.

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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 Model – 10cm Detectors

• Nominal design, hybrids glued to top of silicon

• Section shown below. Detailed properties in Backup

• Detector heating from parameterization of Unno at MIWG 11/07

• Vary chip power(0.125-0.5W/chip) and detector power 1 or 2 mW/mm2 at 0C

• Vary wall temperature of cooling tube to simulate different coolants and to see runaway.

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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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More Thermal Performance• Variants to lower temperature(with either more material or more cost or both)

– “Triple-U” tube(see picture below). This would decrease the T by very approximately 4C in the temperature region of interest for the nominal design.

– Carbon-carbon(that has much higher thermal conductivity through thickness) but gain <2C and not worth much higher cost.

– Small gain(~1C) possible with fiber(eg. K1100 instead of K13D2U) that has higher axial thermal conductivity(by about 40%) but somewhat higher cost.

– Thermally conducting foam rather than honeycomb would gain 2-3C.

– Multi-part bus cable(not cover all of detector area). TBD

• Conclusion from these studies depends obviously on coolant, chip power and prediction of detector power– If CO2, can have significant headroom

– If C3F8, headroom reduced compared to CO2(no surprise) by ≥10C but still may be acceptable.

– If C2F6/C3F8 mixture somewhere in between

• In all cases, need to validate with measurements on full-scale prototypes

- -

-

Note that T is referenced to tube wall temperature in this talk

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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

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More Bridged Hybrid

• Enclosed model in “box” to estimate effects of air conduction

• Preliminary result for 0.25W/chip and zero detector power is a T of about 4C compared to about 6.5C for the nominal design(same coolant conditions)

• Chip temperature about 2.5C higher than detector T

• Thermally comparable to nominal design, studies continuing(also see Backup)

Air box

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Material

• The total radiation length of the mechanical/cooling structure depends on the support conditions.

• If one assumes a shell-like support, then just the stave mechanical/cooling structure (for the nominal design) has a radiation length of about 0.4% (based on measured weights of the prototypes).

• This does not include coolant, modules or bus cables and most importantly not the shell or supports to it.

• For reference, if one assumes end-supports only (not shells) 1m meter apart, then the stave radiation length for comparable deflection would be about 0.9% because stave has to be stiffer.

• In short, one needs a combined stave-support-structure design to get a realistic number.

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Miscellany

• Outer barrel, long strips, with single hybrid for 10cm detectors.– Quick look at thermal performance and T to hottest point on silicon is

about 3C for 0.25W/chip and 0 detector power in nominal design. More than expected from ¼ scaling by power but <1/2 of short strips.

• Distortions as detector cools down– <10 microns distortion out-of-plane calculated for about 50C

temperature change but only done so far for 0.7mm facings. Need to do for thinner facings.

• Gravity sag– A non-issue with shell-like support and frequent supports. Tune

structures to meet requirement.

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Hermiticity and Endcaps• Hermiticity

– In nominal design, there are gaps(eg. 100 microns) between adjacent detectors on same side of stave.

– Mechanically at least one could offset(in Z) the top and bottom detectors such that overlaps do not line up.

– But what can you do if you want hermiticity on each side by overlapping detectors in Z?– Simplest mechanical solution is to have ½ the modules glued to bus cable and the other

half with about 0.5mm carbon fiber plate(with appropriate cutouts) glued to bus cable, raising ½ of the modules to allow overlap – see cartoon below. T would increase for these <1C (for 0.25W/chip, 1mW/mm2 nominal design, not bridge)

• Endcaps– Purely from a mechanical/cooling aspect, one could make pie-shaped segments, routing

the cooling tube as needed to achieve the same thermal performance as barrel staves. Likely offset slightly front and back facings to avoid complete gaps. Straightforward (as would be the support of these into a disk)

– But, but this doesn’t address the considerable problems associate with detector layout or bus-cable-like connections…..

Z

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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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Production – Mechanical/Cooling ONLY

• Rough numbers for barrel only(including guess for yields)– 250 1m staves

– 300 2m staves

• Materials for nominal design– 100 kg of fiber unitape

– 100 m2 of honeycomb or structural foam

– 105 cm3 of thermally conducting foam (if used)

– 600 tube sets(tubes, fittings)

• Production rate 1-2/day required

• At minimum, industrial production of subcomponents (facings, honeycomb/foam pieces, bare tubes…) but full industrial production feasible (with substantial lab QC oversight).

• Very rough guess for technical production labor(not including design or prototype phase or cable attach or anything related to module attachment) is 15 FTE-years

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Risks – Mechanical/Cooling ONLY– Identify components which are ‘single-source NONE for nominal design. – List components or assembly steps which need to be developed or which need qualification before

they can be adopted e.g.• Critical decisions before starting real design: what is coolant and bridged hybrid or not• Interfaces(primarily electrical, where are the connections to electrical services)

– How deep is the assembly pipeline? i.e. what level of prototyping effort is required to fully validate design? Would clearly have to build full-scale prototypes for thermal performance/stability

– Risk due to tight mechanical tolerances during assembly Moderate, mitigate with QC (CMM)– Grounding & shielding risks (by external experts) e.g.

• See electrical department……– Options available for repair i.e. the risk of damage being unrepairable.

• Module/stave damaged during shipping or testing Replace module or toss out• Module/stave damaged during assembly to structures Replace module or toss out• Cooling channel damaged during or after assembly. During, replace, after toss out(before module attach)• Service cable damaged during/after assembly Don’t know yet• Failure after integration. If design requirement(I don’t think it is), make stave replaceable

– Flexibility or options to modify the design based on experience with ATLAS. • Could the material be reduced further? And at what cost? Some but more design time and prototypes• Could additional measurement layers be introduced? Sure• Are there options to improve the mechanical stability? Easy but more material• Are there options to improve the cooling i.e. remove more power and/or lower temperature? Yes, many• Are there options to improve grounding and shielding? Talk to electrical department

– Other technical, schedule or financial risks• Need more studies of pipe(Al) in potential contact with carbon, although lots of work already done for existing

pixel system• Mechanical/cooling ONLY part is of moderate risk. Not easy but not hard

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R&D Plan – Mechanics/Cooling ONLY

• If this approach, then what would be development plan?

• Need to design, build and test realistic prototypes(eg. 1m length) that simulate well thermal and mechanical expectations.

• But it does not make sense to do this before making some essential decisions– Coolant

– Hybrid type(bridged or not)

– Hermeticity

– At least preliminary definition of critical interfaces(mounts and electro-optical)

• Given these choices, estimate it would take about one year to design, build and test full-scale prototype(s) for thermal and structural performance

• Concurrently could develop preliminary production plan and associated cost

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Next Steps

• Respond to questions from review panel• Apart from this does not make sense to do

much more mechanical/cooling design work or prototype fabrication for this concept in the next months.

• Need feedback from making 1m functional prototype with real modules

• And decisions on requirements and constraints