Thermal management for ATLAS upgrade

Georg Viehhauser

30/10/08 2

Organisation• Common understanding that thermal management in

ATLAS has been more painful than necessary.– Thermal management comprises

• High thermal conductivity materials (this is the aspect which did belong to subsystem designs and has worked out well),

• Cooling (external plant and on-detector components like HEXs and heaters, services like pipes and fittings, etc.),

• Environment (thermal enclosure, humidity incl. monitoring, etc.).

• Attributed to absence of any coordinated management structure & lack of effort until late in production.

• For upgrade: Thermal management working group established as first subgroup of the upgrade project office.

30/10/08 3

(Original) remit of the TMWG• Cooling technology

– Quick agreement: go evaporative again– Various candidate coolants: Fluorocarbons (C3F8, C2F6) or CO2.– Address issues like

• Control: Fixed vs variable mass flow.• Throttling

• Pipework and Fitting specification• Test facility design and manufacture

– During ATLAS assembly several C3F8 have been built in parallel with very different designs – duplicate efforts

• Environment– Thermal enclosure – Humidity environment

• Monitoring – Cooling system– Environment

• Materials including thermal interfaces– This is now covered by the subdetector collaborations.

30/10/08 4

Key requirements• About 10°colder than present ATLAS ID(coolant

temperature -35°C instead of -25°C)• ~2× power of present ATLAS ID(~100-150kW

instead of 60kW), – increase in size and channel density, – but reduction of power per electronics channel.

• About 800 supermodules/staves.• High reliability and robustness against failures.

– Failures should not affect large sections of experiment.

– Access to complex objects (HEXs, heaters, etc.)

30/10/08 5

Coolant options • C3F8

– By 2017 we have ~10y of operational experience. Reduce start-up hiccups if we can develop an adiabatic upgrade plan.

– But: It is not clear that a pure C3F8 system can achieve the evaporation temperature.

• Tevap = T(pevap) and pevap = psuction + Δppipe + Δpbpr • We have to address this already for the existing system.• Various strategies under consideration:

– Lower psuction: surface condensers, multi-stage compressors,– Avoid Δpbpr: evaporation pressure control through cold condensers,– Lower T(pevap): Use C2F6/C3F8 mixtures.

• CO2

– Expect smaller mass flow (large latent heat), smaller pipes (large HTC), albeit probably thicker wall.

– Higher pressures (pmax ~50-100bara, pevap~10bara). • Not a fundamental problem, but needs careful engineering.

– No danger of restricting environmental legislation.• Industry’s future coolant of choice.

• The decision needs to be made soon (impact on detector design).

30/10/08 6

A major constraint for ATLAS upgrade

Reuse existing services running from z=0 (outside calorimeters) to end of calorimeter to reduce shutdown time.

– These services run underneath innermost μ layer, which should not be disturbed to shorten shutdown.

– This has never been formally evaluated and decided (too complex), but became widely accepted.

– This provides a limitation• In diameter and number (issue for C3F8: limits possible reduction in

return line pressure drop).• Due to pressure specification (issue for CO2: present Cu/Vulkan Lokring

pipework only good to 30 to 50bara).• Due to lack of insulation:

– transfer pipes need to be warm (above dewpoint ~15°C),– conservative estimate: feed pipes @ 35°C due to environment (cables),– this increases the input vapour quality → reduces the available latent heat→ increased system complexity (requires pre-cooling HEXs, requires heaters)

and drives up the feed pressure for coolants with low critical pressure.

30/10/08 7

ID

A possible solution: multi-stage system

• Primary (plant) stage: – Conventional (oily?) Compressor-condensor-

throttle-evaporator system.– Technology (coolant) is flexible.– This has warm transfer pipes (if CO2 with high

feed pressure ~100 bara).– Evaporates at ~ -40°C.– Return lines have electrical heaters (accessible)

to keep return fluid warm.• Secondary (detector) stage:

– Condensor-pump-evaporator– This would have cold, low-pressure lines.– Condenses at ~ -40°C, evaporates at ~-35°C.– While in principle you don’t need a throttle

(capillary), it will be required for control of the circuit and flow balancing.

– To minimize mass flow (pipe diameter) the coolant in this stage will be CO2.

• Thermally connected by HEX at PP2– Throttling, back pressure regulation and heater

close to HEX → accessible (~1d) and “moderate” radiation.

Calorimeter

Inner muon

Middle muon

Access

Conceptual, not to scale

detector

Q

Q

Q

30/10/08 8

Pipework• In ATLAS

– Poorly evaluated technologies and procedures,• Aluminium pipes: corrosion problems due to alloy choice and handling

mistakes,• Home-made connections developing leaks.

– Poorly specified leak-rate requirements,• Varying from section to section.

– Learned a lot about QA too late• E.g. X-rays of welds etc.

• Upgrade:– Develop a coherent set of specifications for all components,– Specifications for components where possible (base on industrial

standards where possible),– Definition of specification procedures for new (homemade) solutions,– Ultimately possibly specifications of components (fittings, etc.),– This specifications (components and procedures) should be used at all

stages of the project (design, assembly, commissioning, running),– This task is formidable, but could/should be of wider interest.

30/10/08 9

Risk analysis

• In the past – Done late with insufficient resources and expertise– has been usually a fault mode analysis, not a risk

analysis.

→ often retroactive, not part of design decisions.

• Should be– Expanded to reliability analysis and as such should

influence design.

• Will need to learn a lot about this…

30/10/08 10

Future organization • So far there has been a split into present system

and sLHC upgrade.• In the future there will be global ATLAS structure

on cooling including– Current system operation,– Improvements to current system to reach ATLAS final

specifications,– Cooling for the insertable B-layer (innermost Pixel),– ID cooling for sLHC upgrade.

• Details are being worked out right now. Sharing of resources, brainpower and information needs to be organized.

30/10/08 11

Some cooling contacts in ATLAS

Rather than listing all groups and individuals I will list a few contacts which then can guide you on.

– Present system operation: Steve McMahon, Koichi Nagai,

– C3F8 upgrades: Greg Hallewell,

– CO2 cooling: Bart Verlaat, Nigel Hessey,

– Pipes and connectors: Jason Tarrant,– CF pipes: Danilo Giugni.

Backup slides

30/10/08 13

Carbon Dioxide: Pressure - Enthalpy Diagram

Mel

ting

Lin

e

-40

-20

-20

t = 0

oC

0

20

20

40

40

60

60

80 100

120

140

160

Ent

ropy

= -

2.30

kJ/

kg,o

C

s =

-2

.20

-2.1

0

-2.0

0

-1.9

0

-1.8

0

-1.7

0

--1.

60

-1.5

0

-1.4

0

-1.3

0

-1.2

0 -1.1

0 -1.0

0

-.70

-.90

-.80

-.30

Sub

limat

ion

Line

Triple Point (5.18 bar, -56.558 oC)

r = 1200

r = 1150

r = 1

100

r = 1050 r =

1000

r = 900 r = 800

Density = 700 kg/m3 r = 600

r = 500

r = 100

r = 75

1

10

100

1,000

350 400 450 500 550 600 650 700 750 800 850

Enthalpy, kJ/kg

Pre

ssur

e, B

ar

Mode #1, Full Power

From Auke Colijn

30/10/08 14From Vic Vacek

30/10/08 15

From Vic Vacek