Helium Cooling System for the Mu3e Experiment
Constantin Tormann
On behalf of the Mu3e Collaboration
22.03.2018
Mu3e Experiment
Search for the charged lepton flavour violating decay µ+→e+e−e+
Target Inner pixel layers
Scintillating fibres
Outer pixel layers Recurl pixel layers
Scintillator tiles
μ Beam
• Stopped muons decay in a solenoidal magnetic field of B=1 T
• Low momentum electrons pe ≤53 MeV/c
→ Need low material budget to reduce multiple scattering
→ Gaseous helium cooling system for pixel detector
Helium Cooling System
Layer 1 Layer 2
Scintillating Fibre Layer 3
Layer 4
36 cm
Detector modules
• Xx
0 ≈0.1 % for each layer
• V-folds for Layer 3 and Layer 4
→ Additional flow channel
Helium Cooling System
Layer 1 Layer 2
Scintillating Fibre Layer 3
Layer 4 20 m/s
36 cm
20 m/s
Helium Cooling System
Layer 1 Layer 2
Scintillating Fibre Layer 3
Layer 4 10 m/s
10 m/s 5m/s
36 cm
Helium Cooling System
Layer 1 Layer 2
Scintillating Fibre Layer 3
Layer 4 0.5 m/s
10 m/s
10 m/s 5m/s
36 cm
Helium Cooling System
Layer 1 Layer 2
Scintillating Fibre Layer 3
Layer 4 0.5 m/s
10 m/s
10 m/s 5 m/s
20 m/s 20 m/s
36 cm
Simulations for Cooling System
• Expected power consumption per chip area P/A= 250 mW/cm2
→ Test more conservative scenario withP/A= 400 mW/cm2
• Temperatures should not exceed 70◦C
• Helium enters detector with slightly above 0◦C
Testing cooling system using Computational Fluid Dynamics Simulations.
Inner and Outer double layer are presented separately.
Inner Double Layer
Temperature of silicon parts with P/A= 400 mW/cm2
Inner Double Layer
Flow directions in the inner double layers
Outer Double Layers
Temperature of silicon parts with P/A= 400 mW/cm2
Thermal Expansion
Thermal linear expansion ∆L=αL0∆T
Layer 4: L0= 36 cm and αpolyimide = 2×10−5◦C−1
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Avg.Temperature(°C)
250 mW /cm 2
400 mW /cm 2
-60 -40 -20 0 20 40 60
ThermalLinearExpansion(um)
Thermal-Mechanical Chip Prototype
First thermal-mechanical prototype of pixel sensor:
• 50 µm thick silicon layer
• 50 µm aluminium-polyimide flexprint
αpolyimide ≈8·αsilicon
→ Study deformation
Experimental Concept
Initial Temperature
Experimental Concept
Increased Temperature
Chip Deformation
T = 30◦C
Chip Deformation
T = 50◦C
Deformation
2 5 3 0 3 5 4 0 4 5 5 0 5 5
- 5 0 0 - 4 0 0 - 3 0 0 - 2 0 0 - 1 0 0
0
Height displacement h (µm)
T e m p e r a t u r e T ( ° C )
E q u a t i o n y = a + b * x
I n t e r c e p t 4 1 7 ± 3 1
S l o p e - 1 5 , 9 1 ± 0 , 8 6
R e s i d u a l S u m o f S q u a r e s
5 , 1 8 7 0 8
0 1 0 2 0 3 0 4 0
T e m p e r a t u r e d i f f e r e n c e ∆T ( ° C )
Summary & Outlook
• Temperatures in the detector exceed 70◦C for conservative scenario of P/A= 400 mW/cm2.
• Uneven temperature distribution induces mechanical stress.
→ Improve cooling system
• Building thermal-mechanical mock-up for future testing of the cooling system.
→ Validate simulation results
→ Study deformations of detector
→ Study vibrations induced by the helium flow
Deformation Inner Layer
10 15 20 25 30 35 40 45 50 55 60 65 70
250 mW /cm 2
400 mW /cm 2
Temperature(°C)
-20 0 20 40 60 80 100 120
LinearExpansionL(m)
Tubing system
VL4 CEN
GAP L1/2 VL3 CEN
GAP L3/4 CEN
VL4 DS VL3
DS VL3 CEN VL4 CEN
GAP L1/2
GAP L3/4 CEN
GAP L1/2
VL3 CEN VL3 DS VL4 DS
VL4 CEN
GAP L3/4 CEN GAP
L1/2 VL3 DS VL4 DS
GAP L3/Tile GAP
L3/Tile
GAP L3/Tile
GAP L3/Tile
Beam
Pipe 60 m m
er
TileTile
Inlet Inner Double Layer
Inlet Outer Double Layer
Endpiece Layer 4
Endring Blocked Flow
radially outwards
Pressure Drops
Circuit Duct IN Flange Detector Flange Duct OUT
Gap L1/L2 25 7 <1 9 24
Gap L3/Scifi 6 <1 3 28 -
V-Folds L3 25-50 80-90 25 10-20 25-35
Gap L3/L4 8 25 <1 11 -
V-folds L4 30-50 60-70 10-20 50-70 20
Pressures in millibar. Some flows vent into global volume.
Volumetric Flows
Flow channel He flow speed Cross-section Volumetric Flow m s−1 cm2 10−3m3s−1
Gap L1/L2 10 12 12
Gap SciFi/L3 5 105 53
V-folds L3 20 0.7×24×2 20
Gap L3/L4 10 60 60
V-folds L3 20 0.7×28×2 23
Total 238 168
Inlet Outer Double Layer
Inlet Outer Double Layer
Inlet Outer Double Layer
by Thomas Mittelstaedt
