# Presentation: 683642

## ATLAS UpgradeMechanics/Cooling and System Designby LBL

- January 2008

## 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

## 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

## Very Early Concepts

- Foam
- Cooling tube(glued to foam)
- Surface for mounting modules
- Structural support from carbon fiber “skins” glued to foam

- 88mm

## 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”)

## 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)

## 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)
- 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

## 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	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.

- 

- 

## Nominal Design – Short Strips

- Bus cable

- Hybrids

- Coolant tube structure

- Carbon honeycomb or foam

- Carbon fiber
- facing

- 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

## 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 Valencia
- Upgrade R&D meeting in Dec.

## 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

## Thermal Prototypes

- Water at about
- 20C
- IR images
- Before and
- after thermal
- cycling between
- 20C and -35C
- 50 times

- 3.3 W/hybrid(0.55 W/chip)

- No Power

## 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

## Thermal Performance

- C3F8

- CO2

- C2F6/C3F8

- Note in this design, chip
- temperatures are within
- <2C of detector temperature

## 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

## 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**

## 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

## 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

## 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)
- 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.
- Broad role in pixels, building on our experience
- Narrow role in pixels or strips eg. stave design and fabrication
- 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).