1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 1/16
Ageing Phenomena in the LHCb Outer Tracker
1 November 2007IEEE2007
Niels TuningOn behalf of the LHCb Outer
Tracker Collaboration
o Introductiono Ageing Phenomenono Causeo Treatments
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 2/16
LHCb in a nutshell
Aim: look for new physics by measuring CP violation and rare decays
• pp with s =14 TeV• L = 2.1032 cm-2s-1
• 1012 b-hadrons per year
b
s
s
b
b s
μ
μ
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 3/16
The LHCb Tracking System
Tracking Detectors
Outer TrackerStraw tube technologyGaseousMomentumB-mass
Trigger TrackerInner TrackerSi strip detector
Vertex Locatorn-on-n Si strip detector8mm from LHC beam Impact parameter B-lifetime
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Outer Tracker
340 mm Total nr of channels:
53.760 Gas: Ar/CO2 70/30 Anode: 25µm W/Au Cathode: Kapton XC/Al
One large straw tube module: 34 x 490 cm2
4 x 64 = 256 straw tubes
5m
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Position
Good Example:
Check detector response:• Current from 90Sr β-source• Pulse height from monochromatic 55Fe γ-
source
• Full scan of the entire module Every cm2 of the OT is checked
Wire locators
Final Module Check:radioactive source scan
C
urre
nt (n
A)
Example of uniform response
5 meter
Bad Example:
# W
ire
+20%
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Ageing Phenomenon (I)
o Gain loss “in the neighborhood” of the irradiation point:
Croissant? Bean? Kidney? Only at moderate intensity Upstream of gas flow
A real surprise – this was not seen in the aging tests performed over the last years with test modules
Ratio Plot: Iafter/Ibefore Irradiate with 2 mCi 90Sr source150nAGas flow
Ageing Studies in R&D phase with test module:
o 12 MeV proton beamo Hadronic environment (in situ HERA-B)o 9 keV X-ray tube:
Intermezzo:Ageing Studies in R&D phase
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IEEE 2004 NSS-MIC conference (Oct 2004, Rome) by Sebastian Bachmann Session N39: Radiation Damage Effects II - Aging of Gaseous Detectors Title: Ageing Studies for the Straw Tube Detectors for the LHCb Outer
Tracking System
Accumulated 3 C/cm in 120 daysNo effects seen
Ageing Phenomenon (II)
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 8/16
o Gain loss “in the neighborhood” of the irradiation point: Only at moderate intensity Upstream of gas flow
Gas flowRe
lati
ve g
ain
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 9/16
Wire InspectionDeposit on the surface?
Carbon
Non-irradiated wire
Irradiated wire
SEM-EDX:
Optical:
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Find the Culprit(s)
Philosophy:• Create module without glue• Add component by component, until it
ages
Normal F-module:20 hrs, 20mCi
Test module (straws):480 hrs, 20mCi
Test module
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Find the Culprit
Put fresh glue at straw entrance Ageing
Test module:17 hrs, 2 mCi
In parallel, new test modules are built with different glue Confirm malicious effect of glue
Glue: AralditeAW103, HY991
Ageing: Treatments (I)
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 12/16
• Beneficial effects: Heating (2 weeks at 45
oC) Flushing HV training
No heating: 20 hrs 2mCi 90Sr
With heating: 325 hrs 2mCi 90Sr
Ageing: Treatments (I)
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• Beneficial effects: Heating (2 weeks at 45
oC) Flushing HV training
Flushing Time (weeks)
G
ain
loss
(%)
No heating: 20 hrs 2mCi 90Sr
With heating: 325 hrs 2mCi 90Sr
½ year
Detector is installed, and flushing since 1 year
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Ageing: Treatments (II)
• Beneficial effects: Heating Flushing HV training (24 hrs, 1900V,
G~700k) Dark current ~ 10µA / wire Wire inspection promising;
no carbon deposits despite large currents
2nd HV training
1st HV training
3rd HV training R
elat
ive
Gai
n
Irradiation Time (hours)• Other beneficial effects:
Lower gas flow during operation Addition of O2 to counting gas
Ageing: Treatments (III)
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• Other beneficial effects: Lower gas flow during
operationAr/CO2 70/30, 22hrs, 20 l/hr
Ar/CO2/O2 70/27.5/2.5, 46hrs, 10 l/hr
Addition of O2 to counting gas
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 16/16
Summary
o Observed serious gain loss with modest irradiation No gain loss at highest intensity No gain loss downstream the source
o Outgassing glue is found to be the causeo Various treatments have been identified
Flushing Heating HV training Lower gas flow Addition of O2
What science we’ll know in 2050
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 17/16
o The December 1999 issue of Scientific American, cited eight questions to which science is likely to have found the answers by the year 2050:
Can physics be unified?
Can aging be postponed?
How was the Universe born?
How does the mind work?
What secrets do genes hold?
Can robots be intelligent?
Is there life in outer space?
How much do we change the climate?
Backup slides
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Consequence for LHCb?
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o Difficult to predict consequence: Relate source to LHCb
Source LHCbnA/straw
/cm
nA/straw
/cm
Consequence for LHCb?
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 20/16
o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects
• Multiplicative? Extrapolate damage to 108
s• Linearly?• Exponentially?
20 hrs 90Sr
320 hrs 90Sr
(~106 s)
Gas flow 5l/h
(1V/3.6 h)
Extrapolateexponentiall
y to 3×107s
Extrapolatelinearly
to 3×107s
×1/2 ×7 ×26
Heated Module - 2% 1% 7% 26%Flushed Module 2% 15% 8% 56% -
NBAll numbers are for the region of maximum damage (“hot spot”)E.g. 10 cm (in Y) away from that, numbers have to be scaled down by a factor 23
Consequence for LHCb?
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 21/16
o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects
• Multiplicative? Extrapolate damage to 108
s• Linearly?• Exponentially?
Low gas gain cell efficiency
• Gain drop of 50% is roughly equivalent to a HV step of ~70 V
• Assume an initial operational voltage of 1520 V Gain drop of 50% ~ effective HV reduction of 70V ~15% lower drift-cell efficiency
Consequence for LHCb?
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 22/16
o Difficult to predict consequence: Relate source to LHCb Add all beneficial effects
• Multiplicative? Extrapolate damage to 108
s• Linearly?• Exponentially?
Low gas gain cell efficiency
Cell eff track efficiencyTr
acki
ng e
fficie
ncy
OT-cell efficiency
Nominal
An OT-cell efficiency 15% lower than nominal over the entire detector surface induces a 8% reduction of the tracking efficiency
CAVEATThis study is purely illustrational! tracking is not optimized to handle significant reductions of cell efficiencies the gain loss and thus the reduction of cell efficiency is far from being uniform!
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Reverse gas flow
• Only ageing close to input• Polution not caused at curing
time Classical outgassing after
all
Gas flow
Gas flow
Close to output
Close to input
(12 Jun 07, #24)
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Reverse gas flow, check other output now
• Only ageing close to input• Polution not caused at curing
time Classical outgassing after
all
Gas flow
Gas flow
Close to input
(14 Jun 07)
Confirm Gain Loss with 55Fe pulse height
1 Nov 2007 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning 26/16
• Gain loss measured with Current from 90Sr Pulse height from 55Fe