Development of cryogenic silicon detectors
for the TOTEM Roman pots
S. Grohmann, CERN ST-CV
RD39 Collaboration
Seminar on Solid State Detectors
July 11, 2001
Table of contents
u
u
u
u
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Introduction / Roman pots in TOTEM
Cryogenic silicon detectors
Principle of cooling
n
n
n
n
n
n
cooling methods
working fluids
prototype layout
circuit components
two-phase flow pressure drop and flow boiling
test circuit design
Conclusion
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Integration of the TOTEM Roman pots
in LHC
≈ 94 m, 154 m and 180 m from IP5
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Layout of a Roman pot station
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Cryogenic silicon detectors in the
Roman pots
Detectors:
u x-y strips
(10 µm spatial resolution)
u edgeless (min. distance
to the beam 20 σy)
u circular dent
u overlapped
(relative alignment)
u vacuum insulation
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Edge current vs. bias potential and
temperature
- Preliminary results 102
106
Sensor 1, T = 150 K
105
Sensor 2, T = 130 K
101
104
Current (µA)
Current (nA)
U = 500 V
103
102
101
100
100
10-1
Sensor 1
10-2
102
103
10-2
100
Reverse bias potential (V)
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b)
Sensor 2
a)
10-1
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150
200
250
300
Temperature (K)
6
Module design
APV25
Hybrid
Pitch
Adapter
Support
Cooling
Pipe
Detector
Spacer
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Summary of heat loads
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Temperature ranges for cryogenics and
refrigeration
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“Conventional” way of sensor cooling
at cryogenic temperatures
u sensor directly attached to a cold
finger (stirling or puls-tube)
vibrations, space
or
u separation via copper braid
small distance, mass
fluid circuit with direct evaporation
to fulfill requirements in TOTEM
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Working fluids for
evaporative cooling at 120 K
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Cooling Methods
Joule-Thomson Process
10000
log p, h-Diagram for Argon
pressure p
[kPa]
Data Source: GASPAK, Version 3.30 (Cryodata Inc.)
q C = 1.6 q 0
T is
381 K
168 K
120 K / 12.2 bar
1000
iHX
η is = 0.7
110 K / 6.7 bar
x = 0.1
300 K
x = 0.8
wt
q0
100
-120
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-80
-40
0
40
80
120
160
200
240
enthalpie h
[kJ/kg]
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Cooling Methods
Flooded System
10000
log p, h-Diagram for Argon
pressure p
[kPa]
Data Source: GASPAK, Version 3.30 (Cryodata Inc.)
(w t)
q0
1000
110 K / 6.7 bar
x = 0.5
q C = q0
100
-120
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-80
-40
0
40
80
120
enthalpie h
[kJ/kg]
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Principle of cooling
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Heat Sink
Gifford-McMahon
Cryocooler
Integral Stirling
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Thermal interface
condenser / receiver
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Cryogenic Micro Pump
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Two-phase flow pressure drop
in microchannels
In microchannels:
In general:
u frictional, accelerational and
hydro-static term
u correlations for homogeneous
and separated flow models
(dh ≥ 5 mm)
u Storek and Brauer:
1
x 1− x
=
+
ρh
ρg
ρl
1
x
1− x
=
+
ηh
ηg
ηl
correction factor for wv > wl
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u tube dimensions are in the
same order of magnitude as
the thermal and hydrodynamic boundary layers
u Reynolds analogy is no longer
valid (Recrit = 200-900)
u no correlation
u few data for single-phase flow
published
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Calculated pressure drop in the
Roman pot detector modules
0.5
Saturation Temperature: 120 K
Cooling Capacity: 3 W
Tube Diameter: 0.3 mm
Mass Flow Rates: Methane 0.012 g/s
Argon 0.043 g/s
12
Integrated Pressure Drop (bar)
Local Pressure Gradient (bar/m)
15
9
6
3
0
Methane (G = 172 kg/m²s)
Argon
(G = 606 kg/m²s)
0.4
xin = 0 ; x out = 0.5
0.3
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
0.00
Quality (-)
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0.02
0.04
0.06
0.08
0.10
Tube Length (m)
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Flow boiling in microchannels
In general:
In microchannels:
u heat transfer depending on:
-
operating conditions
fluid properties
heating-wall properties
phase distribution
fluid quality
u nucleate boiling: α = f (q)
u algorithms only for macroscale
tubes with dh ≥ 5 mm
u Steiner reference quantities:
d0 = 10 mm; m0 = 100 kg/m²s
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u
‘simple’ scaling to our
dimensions increases the
HTC by factor 10
u
different flow profiles due to
relatively large boundary
layers
u
concept of ‘evaporating
space’ and ‘fictitious boiling’
introduced by Peng
u
few data published
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Peng’s nucleation criterion for
microtubes
20000
with
N mb ≤ 1
Water @ 373 K
16000
Heat Flux (W/m2)
N mb
hlv ⋅ a v
=
c ⋅ π ⋅ (v ′′ − v ′) ⋅ q& ⋅ Dh
Methane @ 120 K
Argon @ 120 K
12000
8000
4000
0
0
1
2
3
4
5
Diameter (mm)
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Calculated HTC in the Roman pot
detector modules
Local Heat Transfer Coefficient (kW/m2K)
50
Nucleate Boiling
40
Saturation Temperature: 120 K
Cooling Capacity: 3 W
Tube Diameter: 0.3 mm
Mass Flow Rates: Argon 0.043 g/s
Methane 0.012 g/s
30
20
10
Argon (G = 606 kg/m²s)
Methane (G = 172 kg/m²s)
Convective
Boiling
0
0.0
0.1
0.2
0.3
0.4
0.5
Quality (-)
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Test circuit layout
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Test Stand - Total View
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Test Stand - Cooling Rack
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Conclusion
u Edgeless silicon microstrip detectors are being designed for the TOTEM
Roman pots with their sensitive area as close as 20 σy to the beam.
u Spatial resolution of 10 µm is obtained with a pitch of about 50 µm.
u A circular dent and the detector overlapping allow relative alignment of
the sensors using the measuring data.
u Detectors are cooled by direct evaporation in integrated microtubes,
which provides minimum mass contribution, constant temperature
profiles and extremely high heat transfer rates, and effective decoupling
of vibrations.
u Experiments are under way to study two-phase flow pressure drop and
heat transfer in microchannels and to test the new circuit components.
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