micro-channel co 2 cooling for the lhcb velo upgrade
DESCRIPTION
Micro-channel CO 2 cooling for the LHCb VELO upgrade. R. Dumps, J. Buytaert , A. Mapelli , P. Petagna , B. Verlaat CERN A. Nomerotski Oxford University . Outline. The VELO detector. Key points of the LHCb Upgrade. VELO Cooling requirements. Micro-channel in Si technology . - PowerPoint PPT PresentationTRANSCRIPT
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Micro-channel CO2 cooling for the LHCb VELO upgrade.
R. Dumps, J. Buytaert, A. Mapelli, P. Petagna, B. Verlaat
CERN
A. NomerotskiOxford University
September 3-7
PIXEL2012. International workshop on semiconductor pixel detectors for particles
and imaging. (Inawashiro, Japan) 1
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Outline The VELO detector. Key points of the LHCb Upgrade. VELO Cooling requirements. Micro-channel in Si technology. CO2 cooling principle. First prototypes & results. Next prototypes. Other micro channel cooling projects. Summary.
September 3-7
PIXEL2012. International workshop on semiconductor pixel detectors for particles
and imaging. (Inawashiro, Japan) 2
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The VELO detector.
Cooling: Module power dissipation ~16W Operates in vacuum. Pioneering use of evaporative
CO2 cooling.
September 3-7
PIXEL2012. International workshop on semiconductor pixel detectors for particles
and imaging. (Inawashiro, Japan) 3
Vertex locator of the LHCb detector : select beauty and charm decays.
Excellent hit resolution(down to 4 um).
Impact parameter resolution (13 + 25/pT um).
84 Si strip sensors with varying strip pitch
8 mm from LHC beam
Trigger on secondary vertices for b physics
See talk of K. Akiba,Session 2
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
4
Upgrade of the LHCb detector. Key points:
5-fold increase in luminosity: 2 x1033cm-2s-1
40 MHz event readout. Installation during Long
shutdown 2 in ~ 2018. New VELO modules &
asics : Pixel option is most advanced. Also a new strip module is
pursued. More details were given in
talks by M. Van Beuzekom “VeloPix” in session 5)
September 3-7
Conceptual view of pixel modules.
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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The cooling requirements 12 ASICS: ~ 36W max. Sensor heat dissipation:
Extreme radiation environment After 100 fb-1 sensors accumulate 370 MRad or 8 x 1015 neq/cm2 at 7 mm from beam.
High sensor leakage current & power dissipation : ~ 1Wcm-2 !
The sensor temperature at 7mm must stay below -15 C to avoid thermal run-away.
The maximal total dissipated power density is ~40 W/24 cm2 ~ 2 W.cm-2
This requires a very efficient cooling solution with minimal material impact !
September 3-7
500
50
5Radius (cm)
Dose after 100 fb-1
n eqc
m-2
x 1
016
TID
(MR
ad)
7 mm
Radiation dose profile for Pixel or Strips
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
6
Micro-channels in Si. Cooling tube is integrated in the
substrate: Can customize the routing of channels
to run exactly under the heat sources. Many parallel channels:
large liquid-to-substrate heat exchange surface.
Low mass : No extra ‘bulky’ thermal interface
required between cooling channel and substrate.
No heat flows in the substrate plane:
Small thermal gradients across the module.
All material is silicon : No mechanical stress due to CTE
mismatch.
September 3-7
Top Sensor 150umASIC150u
m
Bot Sensor 150um
ASIC150um
Si Substrate ~400um
Cooling In-outlets
Glue 50um
Micro channels200 um x 70 um
Advantages:
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
7
µ channel fabrication. Process used
for first prototypes by CERN/PH-DT at CMI at EPFL, Lausanne.
September 3-7
Silicon (500 um)
Silicon
Photo resist
Silicon
Silicon
0 – stock-out
4 – Anodic bonding(1KV / 350 C)
3 – Resist Strip & Piranha cleaning
2 – DRIE Etching of channels (~ 70 um)
1 – lithography
Pyrex (500um)
Silicon
Pyrex
Silicon (200-150-100 um)Pyrex
5 – thinning
Pyrex
SiliconPyrexPhoto resist
6 – lithography
7 – DRIE Etching of inlets
8 – Stripping 9 – dicingPyrex
SiliconPyrex
Pyrex
SiliconPyrex inlets
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Evaporative CO2 cooling.
September 3-7
Enthalpy (J/kg)Pr
essu
re (
Bar)
Liquid
2-phase
Gas
Isotherm
Sub cooled liquid 2-phase liquid / vapor
Dry-out zoneTarget flow conditionTem
pera
ture
(°C
)
Fluid temperature
Low ΔT
-30
0
30
60
90
Increasing ΔT (Dry-out)
Tube temperature
vapor
CO2 is boiling
- CO2 absorbs heat from environment to raise its enthalpy (internal energy). - this happens at nearly constant temperature.
Temperature is defined by pressure. -56 C < T < +31 C 5 bar< P < 73 bar
What happens inside a cooling tube ?
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Modeling & channel dimension. Model simulation (“CoBra”)
with channel parameters: length =120 mm, absorbed heat = 1.5W, Temperature at inlet = -20 C Vapor quality at exit =0.8
This model does not include : coupling between parallel channels Square tubes.
CO2 is optimal for small channels ! Also CO2 has a low viscosity and
high latent heat, which contributes to less pressure drop and smaller mass flow, leading to smaller channels and lower total mass.
September 3-7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
1
2
3
4
5
6x 10
-3
Tube diameter (mm)
Vol
umet
ric h
eat t
rans
fer c
ondu
ctio
n (W
/mm
3 K)
Overall volumetric heat transfer conductionL=0.12 m, Q=1.5 W, T=-20 °C, VQ=0.8
CO2 (19.7 bar)
Ethane (14.2 bar)C2F6 (10.5 bar)
Propane (2.4 bar)C3F8 (2 bar)
Ammonia (1.9 bar)R134a (1.3 bar)
Optimal Ø (round tube) ~ 250 umSquare tube 70x200 um2 ~ 133 um Ø (round tube)
Volumetric heat transfer conduction = with Q = absorbed heat V = volume of tube dT= T(tube) – T(liquid).
QV.dT
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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First prototypes
September 3-7
The aim is to: Demonstrate CO2 circulation in micro channels. Measure
the cooling performance the pressure resistance.
60 mm40 mm
In- & outlet holes (Ø 2mm)Input restrictions
(30 um width) to equalize the flow across all channels
15 cooling channels(200 um width)
transition of restriction to channel
“Snake” layout
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Test stand
September 3-7
CO2 cooler “Traci”: Temp: +25 C to -40 C cooling power: 400W
Infrared camera pictures taken through IR windowsDevelopment of a hotspot caused by dry-out of CO2
Test sample equipped with cooling tubes, heater and pt100 probes
Vacuum vessel with visible and IR view ports.
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Pressure resistance.
Then successfully used Si-Pyrex instead (more robust & faster).
with Pyrex thickness of 500um : pressure tested OK up to 30 bar.
with Pyrex of 2 mm: OK up to 69 bar. (=PCO2 @ 25 C).
September 3-7
Silicon
tp
W
0 0.5 1 1.5 20
50
100
150
200
250
300
350
400
450Rupture Pressure for Silicon Cover
tp=50µ
tp=200µ
tp=350µ
Manifold Width (mm)
Pint
(Bar
)
Width (mm)
First unsuccessful trials with Si-Si bonding : (failure due to contamination in apparatus).
Structural analysis with ANSYS 2D.
Target
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13
Cooling power test.
September 3-7
PIXEL2012. International workshop on semiconductor pixel detectors for particles
and imaging. (Inawashiro, Japan)
Tem
pera
ture
(C)
In & outlet pressures
Various temperatures.
Pres
sure
(bar
)
Time
1. CO2 enters micro channels.Sample cools down to 0 C
2. Heater is switched on/off.
3. CO2 pressure is lowered.Temperature decreases to -26 C.
-27 C
Heating power is increased stepwise
CO2 can no longer evacuate heat : “dry-out”
Cooling power achieved:1.9W/cm2 at T= 0 C, 0.5W/ cm2 at T=-27 C
Limited by achievable mass flow (pump limit)Expect much higher with improved pump !
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Next prototypes. Aim to prove pressure resistance
Beyond 100 bar on large number of small size samples (~100).
Experiment with The variation of the channel pitch. The geometry of the outlet manifold
Must use Si-Si fusion bonding. Select a commercial supplier : LETI,
Grenoble. (8”wafers) Quality assurance.
Scanning acoustic microscope Knife edge tests, etc… Thermal cycling
September 3-7
15mm30mm
30mm 30mm
Hole size reduced to 0.5 mm Ø
Towards a “double snake” for a full module 105 mm
60 mm
In/outlets
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
15
Microchannel substrate
Inlet & outlet tubes(1.6mm outer Ø)
Cover plate
O-ring or glue18mm
Custom fluidic connector. NanoPort connectors (Upchurch
Sientific,UK) are guaranteed up to 103 bar, but bonded to surface with adhesive
polymer rings : radiation hardness, long term performance are unknown.
We started a design of a more rugged connector at CERN.
Micro-channel substrate is clamped between two metallic pieces, tightened with screws.
Tubes are welded in bottom piece. O-rings or glue seal gas tightness. Not yet optimized for lowest mass
September 3-7
11 m
m
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Other micro channel projects.
September 3-7
2012
Cooling requirementsminimize material below detectordetector area: 60 x 27 mmT on Si detector: -20ºC ÷ 5ºC ∆T over detector: 6ºCHeat dissipation by read-out chips:
4 W/cm2 in the periphery (Digital)0.5 W/cm2 in the center (Analog)total 48 W
thin silicon plate (130 µm)C6F14 liquid (8bar)
NA62 Gigatracker
2012
cooling µ-channels only under asics.no material under sensorTotal heat dissipation 21W.T sensor ~ +20CEvaporative C4F10 Pressure 2 bar
ALICE upgrade pixels
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PIXEL2012. International workshop on semiconductor pixel detectors for particles and imaging. (Inawashiro, Japan)
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Summary. The upgraded VELO modules require a very
efficient thermal management: low temperature, high power density & low mass.
The innovative combination of CO2 evaporative cooling and micro channels in Si is a promising solution.
We are addressing the main outstanding issues of high pressure resistance & connectivity under vacuum conditions.
Micro channel cooling is rapidly gaining popularity in new pixel detector projects.
September 3-7
Arigato !